The 38/250 Supercharged Super Sports Mercedes-Benz
In the past specialist articles on outstanding sports-cars have been a much appreciated feature of Motor Sport. In this series the "12/50" and fwd Alvis, the sv twin ohc and Bertelli Aston-Martin, the 3, 41/2, 61/2 and 8-litre Bentleys, the "30/98" Vauxhall, the Lancia Lambda, the Hispano-Suiza range, the Sunbeam range from 1919 to 1935, the Amilcar, the "14/40" Delage, the 2-litre Lagonda, the HE, the Ballot range, the GN, the Singer Nine, the MG Midget, and the Austin Seven have been amongst the cars comprehensively described from the aspects of specification, evolution, performance and servicing. As almost all the back issues concerned are now out of print, there is no point in giving the dates when these articles were published ; however, we can usually arrange for those interested to call at our offices and see the article in the file volumes.
The present article covers that immortal sports car, the "38/250" Mercedes-Benz, and has been prepared for us by RH Johnson, who is particularly interested in this marque and who until recently ran his own "38/250" SS four-seater at Club race meetings. He intends to form a Mercedes Register, about which an announcement appears elsewhere in this issue.—Ed.
Throughout the stirring history of motor sport few cars have quite achieved such fame or aroused such intense enthusiasm as the "38/250" Mercedes-Benz. It is almost unique in having acquired an idealism which finds expression in such emotionally descriptive terms as "immortal" or "legendary," so often used by writers and advertisers when referring to this car. As regards the latter suggestion, unlike most legends; the facts are indisputable, for the "38/250" on its first appearance in an international meeting in this country, the 1929 Irish TT, achieved a sensational victory in appalling conditions when Caracciola completed what is generally regarded as the outstanding drive of his career, often referred to, indeed, as the greatest drive in motor racing history. It was a sad day for the "wearers of the green," for three blower "41/2" Bentleys failed to catch this white production model sports car, which was destined to develop into a highly-successful Grand Prix winner, perhaps the only production sports touring car ever to achieve this distinction with such slight departure from production specification.
There was, however, something more about this car than its victories which fired the imagination of the sports-car world. This was a car simply breathing the indefinable as contained in that eternal question, "What constitutes a sports car ?" The appeal lay in the embodiment of a refined balance between the symbolic artistry of speed, sleekness and sheer power, which no other design had succeeded in translating into a thing of beauty, nor has it been equalled since. Perhaps no more imposing-looking sports-car has ever been conceived ; it was the ultimate of its kind and to this day is regarded by many as the most classic sports-car of all times. In the words of "Minty" Scott-Moncrieff, that well-known Mercedes connoisseur, "Mention of the name '38/250' makes all true vintagents drool at the chops," and, as remarked by the Editor of Motor Sport, after his road test in November, 1929, "Words fail me—this is the most amazing motor car it has ever been our fortune to drive."
In the book "Continental Sports Cars" by W Boddy, the salient features and successes of the "38/250" are admirably presented in the available space. Infornation and data on this car are surprisingly rare considering the tremendous impression it made on the motoring world. With this premise, the author hopes that the description which follows will contribute a little more information to the general knowledge.
The first of the big six-cylinder sports models from which was evolved the "38/250" was known as the Model 33/180K, with a supercharged engine of 94 by 150 mm (6.245 cc), These models first arrived in England towards the end of 1920, being described in road test reports as the first genuine 100 mph touring cars.
At the 1927 Olympia Motor Show Mercedes-Benz exhibited for the first time since the close of World War 1 and a sensational come-back was staged by introducing the Model 36/220S, which was bigger and better than the "33/180." It had a supercharged engine of 98 by 150 mm. (6,789 cc). This model had a lowered chassis and radiator and was a definite breakaway from the upright vintage styling of its predecessor. It was capable of speeds well in excess of 100 mph and secured many victories in international road racing.
The opinion is held by some that the "36/220" is a more flexible car to drive than the "38/250" and, as Mr Edward L Mayer (who can well deserve to be described as the greatest Mercedes enthusiast still living, having owned over 100 different examples of this marque, after a lifetime crammed with experience of Daimler-Benz Aktiengeselschahaft products), still chooses to run an immaculate touring "36/220" and keeps an equally handsome two-seater as a spare car, I am convinced this opinion is not unwarranted. Another excellent example of the "36/220" still with us today is the ex-Earl Howe maroon two-seater now owned for many years by HE Rohll, which is frequently seen competing at VSCC and BDC Silverstone Meetings.
But now we must pass on to the subject of the article. The Model 38/250SS (Super Sports) had already demonstrated its capabilities during 1929 in the Irish TT and GP races, so that it was with profound respect that the British public had its first opportunity to view this car at close quarters in the 1929 Olympia Motor Show. There are grounds for presuming that production of the SS model was commenced late in 1928, but as it was not shown in the 1928 Olympia Motor Show some doubt exists on this point. Production continued each year, 1929-1934, when it was discontinued in favour of the eight-cylinder 500K. Various type letters and powers were used as nomenclature during this period, as follows :
1929 and 1930—"38/250" SS Super Sport and SSK (Super Sports Kurz), kurz=short.
1931--Grand Prix Sports SS and SSK.
1932---SS and SSK.
1934—Super Sports "37/225"
The price complete ranged from £2,500 in 1930 to £3,085 in 1934. The SSKL. (L for leicht), which had a lightened, copiously drilled short chassis, was not a production model in the full sense of the term. The majority of the few examples of this type were "works" team cars but some were supplied to special order from early 1930 onwards. The author has not as yet traced any example in this country and has been informed that no "pukka" SSKL ever came over here in private hands.
The car in which Caracciola won the 1930 Irish GP, again soundly beating the Bentley team in the process, although frequently referred to as an SSKL model, does not appear in photographs of the race to have a lightened chassis. This description probably applies only to the engine, which will be mentioned later.
Following upon the success of the "36/220" model, it is surprising that its successor was not considerably larger. One would have expected something in the region of 8-litres, as was seen in the development of the 61/2-litre Bentley to the 8-litre, although it must be remembered that these were unblown engines. The "36/220" engine capacity was merely increased by 280 cc by enlarging the bore from 98 mm to 100 mm, the new capacity being 7,069 cc. The extra bhp obtained was assisted by a larger supercharger and slightly different valve lay-out, the extra urge being taken care of by a more robust crankshaft.
The sleek low lines of the "36/220" were subtly transformed by a higher chassis and radiator, giving the "38/250" a more formidable appearance. In the opinion of the writer the only detrimental change was in abandoning servo-assisted brakes. Perhaps in theory the extremely large diameter drums were considered adequate without such assistance but the weight-velocity factor proved greater than had been foreseen. There is no denying that the lack of braking power of the "38/250" constitutes a serious drawback to the enjoyment of anything approaching full performance on roads in this country.
Standard production body-styling by Karosserie Mercedes consisted of a four-seater open tourer, and a two-door, drophead coupe or cabriolet, with either left or right-hand drive to order. No production two-seater sports bodies were made for the long-chassis SS as they were for the SSK, but some excellent examples of two-seater bodywork were provided on the SS by specialist coachbuilders. One outstanding example which springs to mind is the ex-Rothschild, ex-Eccles maroon two-seater with massive chromed external three-branch exhaust cowling. This car has not been seen in the post-war years and it is earnestly hoped that it escaped the ravages of war.
Practically all the leading coachbuilders of the time produced striking examples of contemporary styling on this chassis. Amongst these were Saoutehik of Paris, Erdmann & Rossi, Million-Guiet, Von Castagna, Kellner of Berlin, Vanden Plas, Corsica, Mulliner, Freestone & Webb, etc. The well-known black drophead coupe SSK, recently owned by G Crosier and often seen at Prescott and other meetings, has a Corsica body and was one of two only drophead SSKs in this country. This car has now gone to enrich the eyes and ears of our friends in the USA, and is another example of the serious depletion which is taking place by the loss to this collar of our finest examples of vintage sports cars. We have, however, some consolation in the knowledge that they are going to owners who will cherish them with equal respect.
The overall length of the SS chassis is 15 ft 5 in. The wheelbase is 11 ft 13/4 in, track 4 ft 77/8 in, and road clearance 6 in. The chassis is of deep channel section with an extra strong transverse box-section member about mid-length. It is deeply curved at both ends to obtain a low cg. At the front, long semi-elliptic overslung leaf springs are fitted, with the same, but underslung, at the rear.
Certain chassis possess a front-end whip which, in an extreme cases, caused slight contact of fan blade tip with the radiator. This phenomena is fortunately rare, but that it was appreciated is evidenced by the wire bracing and bottle-screws which were a feature of Caracciolas 1929 Irish TT car when last seen by the writer some years ago.
Wheels are 20 in diameter for 6.50 tyres all round, or sometimes 7.00 on the rear wheels. Construction is of three-spread wire spokes with detachable rim guards and heavy-duty knock-on hub caps.
The transmission is flange-mounted to the engine, through a dry multiple-plate clutch to it four-speed gearbox with chrome-nickel-steel gears and centrally-mounted ball-joint control rod which can be locked in neutral to prevent unauthorised use. The standard gearbox ratios are 8.72, 5.0, 3.76, and 2.76 to 1. The gearbox is in unit with engine necessitating displacement of transmission aft before removal. Reverse gear is engaged by tilting the ball socket and moving to the left forward. Rear-end drive, via a universal joint in a ball housing in which terminates the torque-tube, is by spiral bevel gears and differential housed in a pressed steel rear axle. The standard rear-axle ratio is 2.76, with special ratios of 2.5 or 3.09 supplied to order. The 2.5 ratio is well suited for high-speed track work but noticeably impairs acceleration in sprints.
Steering is high-geared, via a deep worm and nut, and although heavy in manoeuvring becomes the acme of precision at high speeds. This is one of the chief joys in the handling of the "38/250," a point which was spontaneously remarked upon by the late Pierre Marcella as the most perfect he had ever experienced on one occasion of driving the author's car. Turning circle to the left is 50 ft 9 in and to the right 49 ft 10 in.
Shock-absorbers are Roudaille hydraulic both front and rear. The semi-elliptic suspension, hard by modern standards, is just right for a car of this character. Adjustment of the brakes by the handwheel regulators on each leading rod is frequently required and in this respect improvement can be obtained in catching up with the lost movement in the linkages by cutting quarter-turn notches in the rods in way of the handwheels, great care being taken not to overweaken the cross sectional area.
A large fuel tank (benzin enthalten) of 27 gallons capacity is situated behind the rear axle, feed being by Autovac, or by gravity tank on the engine bulkhead and an air-pressure system. Two spare wheels are mounted behind the petrol tank, providing useful weight compensation aft.
Chassis weight is 25 cwt, weight with four-seater bodywork 371/2 cwt, and total laden weight with two people is 47 cwt.
The overall length with four-seater bodywork is 16 ft 8 in and the width 5 ft. 8 in.
The engine has an RAC rating of 37.2 hp, and is a six-cylinder of 100-mm bore by 150-mm stroke, or 428 cubic inches piston displacement (7,069 cc). Total power developed at 3,200 maximum safe revolutions (undrenhungen in der minute) is 170 bhp unblown and 225 bhp blown; bhp to piston area ratio is 3.3 for the SS model. The SSK model with larger supercharger obtained 250 bhp blown, and the SSKL with racing camshaft and "elephant" blower is reputed to have developed 300 bhp.
Of monobloc design with detachable head, the upper portion of the crankcase and the cylinder block is manufactured from a single piece of Silumin. The lower half of the crankcase and the cylinderhead cover is of east aluminium. The sump casing and overhead valve cover are a metal-to-metal fit with the block, the only gasket used being the copper asbestos cylinder-head gasket. The block is fitted with sleeves of grey casting on the wet-liner principle and light metal pistons each with three compression rings and one scraper ring are used. The circular-section connecting-rods are of high-tensile steel and are drilled to pass oil up to the gudgeon pins. The only case of rod failure known to the author in a "38/250" was the unfortunate one of the owner who forgot to turn off his Ki-gass pump !
The fully balanced crankshaft is of chrome nickel steel, with four main bronze-backed poured bearings. The six big-end bearings are also of this type. The cam-shaft is driven by a vertical shaft at the rear end from the crankshaft through silent helical gears. The valves, two per cylinder, are operated by rocker arms. Tappet clearances when warm should be 0.005 in for the inlet valves and 0.007 in for the exhaust valves.
The oil pump is driven by the vertical timing shaft and draws oil from a gauze-enclosed trap in the sump. There is also a special piston pump which meters fresh preheated oil from an auxiliary tank to preserve the maximum sump level. A glass sight is provided in the side of the block to show the level of fresh oil in the auxiliary tank. This is an excellent idea for long-distance high-speed work but in normal conditions it has a tendency to provide too much oil, with consequent fouling of the sparking plugs. On right-hand-drive cars where the Autovac is on the left-hand side of the engine bulkhead, the auxiliary oil tank filler cap is inaccessible and the glass level sight half obscured. This is entirely due to the transposition of the steering column.
Provided normal routine checks on the sump level are made the auxiliary oil tank need never be used. The sump level is ascertained by the use of a three-way tap mounted on the base of the block under the forward carburetter. The first position (moving the hand lever forward) drains off any excess oil over the maximum level (two gallons capacity), the second position (moved forward again) is the minimum safe level, and if there is no discharge at this position—you have been warned ! The third position (again forward) empties the sump. In the position moved aft of the closed position the whole tap can be withdrawn for cleaning. It is not clear what advantage the designers had in mind over the normal dipstick procedure, as the latter at least indicates the amount consumed. One snag about this patent tap is the great care necessary when replacing the sump chamber in order not to jam the housing on its valve seating. Crankcase ventilation is embodied in the bell housing of the tap.
The oil filter is contained in the rear-end crankcase casting and is obtained by unscrewing a large cap: It consists of an unbelievable length of spiral-spring steel, the release of which even whilst cleaning should be avoided at all costs. Once let slip, it will encircle the garage twice and attempt to choke the well meaning liberator !
Standard oil pressure when hot should be 42 lb/sq in (3 kg per sq n. for those with gauges thus calibrated). Maximum oil sump content is two gallons.
The standard compression ratio is 7 to 1. Valve timing is checked by observation of-a number of letters on the flywheel for each position of the four-stroke cycle in No. 1 cylinder.
The Roots-type two-vane, two-lobe supercharger is verlically mounted centrally at the front of the engine. It is gear-driven from the crankshaft to run at three times engnie speed and blows air through the carburetters, unlike its normal British counterpart which sucks the mixture from the carburetter. Dimensions of the standard 81/2 lb/sq in blower fitted to the SS model are : height 283 mm, and outlet port 64 by 107 mm. In effect it, provides an eight-speed transmission, as follows : first gear unblown. first gear blown, and so on up the range of the box. Normally it is out of use, being braked by a special clutch assembly with eight pairs of discs. To operate, the foot throttle is depressed hard down to the floorboard, throwing over a trip-stop which is positioned at the normal full throttle opening (to prevent misjudged use of the blower). The movement is transmitted through rod controls to the driving clutch, which consists of 22 pairs of discs. It is extremely important that the foot throttle be held hard down all the time whilst using the supercharger as it is foot-applied pressure which holds Ihe clutch in engagement. A powerful spring returns the throttle pedal immediately it is released.
The noise of a Mercedes blower is, to the occupants of the car, diabolic. After the first terrifying bursts of boost have been attempted and it is found that the engine doesn't blow up the experience becomes totally exhilerating. The noise level rises like an air-raid siren and becomes demented as a pack of Irish banshees. One literally feels the seat pushing one in the back and wheelspin on a greasy or wet road can produce a complete volte-face. It should be emphisised, for the benefit of the unimpressed who, whilst spectating on track or airfield, have only heard the blower cutting in and out, that a full appreciation can only be obtained whilst in the car. From a distance the blower does not sound aII that impressive but if a mean advantage be taken of an unsuspecting passenger his first impulse is to bail out. [I first experienced this exhilarating sound at the age of 14, in a "30/220 " along the Barnet By-Pass, and on returning home announced that I "felt years younger." Ed.).
An incident, illustrating another Mercedes aspect which should be allowed for occurred after an informal sporting race to Salisbury one Sunday morning when the author overtook Dr WA Taylor of "Alfi-Capa Caesar Special" fame, who, in his 3-litre Bentley was conveying a friend to Salisbury station to catch a train they had already decided was lost. Taking the advantage of sunrise, we cheekily waved on passing, but the Bentley, true to its finest traditions, sensed it had seen a gauntlet dropped and gave chase. The shriek of a Teutonic blower echoed over the Plain that morning as the Druids stirred uneasily in their unterwelt spuken. The terrier 3-litre was shaken off but the Doctor later informed me they caught the right train ! After a good few minutes stop in Salisbury square and when just on the point of climbing up into the Merc, we were indignantly accosted by a most enraged couple whose car, it, appeared, we had passed on the road by using a siren to clear the way, and did we not know this was illegal ? Tempers were rising after the lady had declared it was obvious I had never been taught to drive; calm however was obtained when the bonnet was lifted and a short lecture delivered on the ABC of supercharging.
To return to the technical description, whilst blowing, the Autovac is automatically converted into a vacuum tank in order to balance float-chamber pressure, and a butterfly valve in the air intake of the carburetters is closed whilst under compressed air. A glass sight petrol reservoir is mounted on the dashboard to indicate excess petrol in the Autovac, through which it is free to overflow ; when petrol is observed in the glass, blowing should be discontinued at once..
A point usually ignored or unknown in this country is that the instruction manual expressly states that the supercharger must not be used on gasolene only. A benzole mixture of approximately 50/50 is essential in order to avoid the dire consequences of excessive cylinder-head temperature. It is also not the manufacturer's intention for the blower to be used continuously; 15 to 20 seconds is quite long enough for the purpose for which, it is designed, namely, to increase speed in each gear when hill-climbing. It should, not be used at low speed, nor brought in at high speed in top gear.
The popular opinion held by many is that the "38/250" Mercedes is notorious for blowing its cylinderhead gasket The answer is that any supercharged car will do this if the head is not thoroughly tightened down and when unsuitable fuel is used. The gasket should embody reinforcing around the water holes, not merely be punched through. The author's car, fitted with high-compression pistons, only once blew the cylinder-head gasket, ie when the blower was used in bottom gear up a very steep hill. This was done in the initial exuberance of first ownership and sure enough the head was found to be insufficiently tightened down by the previous owner. To this day it has yet to be proved that the lone "38/250" driven by Caracciola in the 1930 Le Mans Race, was forced to retire by reason of a blown gasket. The best evidence to the contrary is found in the words of the late Sir Henry Birkin, Bt, whose job it was to force the Mercedes with that object in view. In "Full Throttle," he writes : "The Mercedes' second battery was exhausted, the engine would not start nor the lights work, so Caracciola admitted defeat with no shame to car or driver. They had run alone for 10 hours and held more than their own against a meticulously-prepared team of five Bentleys—to have lasted as long as that was miraculous. I retired after 20 hours with a broken con-rod."
A slightly larger blower, compressing at 10 lb/sq in, was fitted in the SSK model, whilst the SSKL had an even larger one producing 12 lb/sq in, with a height of 317 mm and an outlet port of 70 by 111 mm. This latter was known as the "Elephant" blower in England. It is not generally realised that three sizes were available for the "38/250" and many cars which are mistakenly described as fitted with the "Elephant" blower have in fact got the medium-size one. Within recent years only three genuine "Elephant" blowers were known to exist in this country, and now that the ex-Caracciola 1929 Irish TT car and the ex-Crozier SSK have gone to the USA only one remains. It will be recalled that the fitting of one of these large blowers in Caracciola's car for the 1930 Irish TT resulted in his disqualification by the Scrutineers, who contended It was a non-standard fitting, although a few had, in fact, been used on the Continent that year. The main issue was that the "Elephant" blower was not fitted to the production "38/250" Mercedes as exhibited for sale in the Park Lane showrooms, but it was available to special order. It was certainly a border-line case over which most people agreed the scrutineers were at all events scrupulously fair to other. competitors.
This system of supercharging "at will" has much to commend it, in preference to the continuously-engaged method. It has the advantage of economy in fuel consumption, greater reliability due to less use, improved flexibility at low speed and instant acceleration "on tap" which is extremely useful when in a tight spot. [Stutz employed such a system on the "Bearcat".
Normal aspiration is by two huge Pallas carburetters, fitted on the near side of the engine and provided with a hot-air crossover downdraught duct from the exhaust manifold to the inlet manifold. The rear carburetter has a choke device operated from the dashboard. A Ki-gass pump is, however, usually found to be indispensable for easy cold starting. The carburetters rarely give trouble provided the correct combination of jets is used. A box containing a full range of spare jets with special carburetter tools was provided with each car. A choice of petrol system was permitted to order, Autovac or air-pressurised petrol tank ; the latter provided a hand priming pump, with pressure gauge and release cock, fitted on the dashboard. A small air pump is fitted at the rear end of the camshaft to maintain pressure whilst running.
Petrol consumption is not quite as staggering as present-day comments would lead one to believe. Used as a normal touring car a genuine 12 mpg can be relied upon, and with deliberately careful driving 14 mpg is possible, but the man who really drives this car to attain high average speeds and uses the blower through his change-ups must be prepared for a consumption of alarming proportions. The "38/250," one must remember, was designed at a time when petrel was cheap and economy of absolutely no consequence to those who demanded power with performance.
As a point of interest, there exists in this country one "38/250" model fitted with an experimental petrol-injection system but whilst some improvement was obtained in the power curve, little, if any, was found in the consumption.
The water pump is located under the exhaust-side portable cover plate. An automatic grease stuffing-box is provided, with a spring-loaded piston carrying an indicator with red and white diagonal sections. This indicator is observed through a peephole window in the cover plate; when red comes into view it is an indication that the grease cup mounted on the floor of the car requires refilling.
A drain tap is fitted on the pump inlet pipe through which the entire content of the cooling system, including the radiator, can be emptied. The fan is fitted at the front end of the camshaft drive and is provided with a slipping clutch in case of a front-end prang. This unusual feature was first brought to the writer's attention in a startling manner by Mr V Morley, a well-known Mercedes specialist, who nonchalantly grabbed the fan in order the better to pick out which erring tappet was causing noise. Emulation is not recommended, but use the left hand if you try !
The massive vee radiator, mounting the classic Mercedes star pedestal combining temperature gauge and mascot, is the crowning glory of the "38/250." It is of true honeycomb section, the core being cast„ and cost around £50 pre-war. The capacity of the water-system is six gallons, which produces a tendency towards overcooling. It will be found advisable to blank off about one-third of the radiator in cold weather. The implications of this large capacity are only fully realised when the purchase of anti-freeze solution is made !
Most of the competition models are adorned with very elaborate stoneguards of striking design. Various badges have been fitted by the works at different times. The earlier Model S ("36/220") had only an embossed star (not enamelled) on each side of the radiator header casing. Early SS and SSK models had a coloured red and black centre badge in addition to the embossed stars, whilst later models have only the coloured centre badge, altered to blue and gold. Many of the cars exported to the USA carried a written name scroll attached to the honeycomb of the radiator.
Bosch electrical equipment is fitted throughout.
The firing order is 1, 5, 3, 6, 2, 4.
The ignition system is dual, using coil and magneto, the coil supplying sparking plugs are on the exhaust side and the magneto plugs on the inlet side. In the event of failure of one system of ignition, the faulty member can be switched off from the dashboard. A marked falling off in perfornumee is noticeable on single-source ignition but smoothness and pulling remain satisfactory. The correct distributor gap, points fully open, is not more than .016 in although. using a dual distributor head mounted on the magneto, the coil spark-timing is set slightly in advance of the magneto timing. Advance and retard is manually controlled from the steering-wheel boss. When using the supercharger the ignition should be fully advanced. Fully advanced ignition takes place at 45 deg before tdc for coil and 40 deg for magneto. The starter motor is a Bosch, Type BJG 1.5/12 L11, of forward-moving armature type. Starting, by handle of staggering length, is not so hazardous as it would appear as the compression allows of only one pull up per swing from 9 to 12 o'clock, which, on full retard and with the help of coil ignition, plus two shots of Ki-gass when cold, rarely fails. Decompression taps with spring-loaded valves are fitted on each cylinder but require constant finger pressure to open, having no positive lock. They are useful as a quick check on combustion conditions but of no help in starting on the handle.
The recommended sparking plugs for normal touring conditions, using petrol only, are : coil, Champion 16; magneto, Champion 7. For more strenuous work with frequent use of the blower Champion R3V should be used with the coil, and for flat racing Champion R1V on both sides. These are the plugs recommended in the instruction manual alongside the equivalent Bosch grading. The electrode gap should be 17 to 20 thou inch.
The dynamo supplying automatic regulated current to the high-capacity 12-volt battery is mounted under the cast-aluminium engine cover plate on the off side of the engine and driven in tandem with the magneto and water pump.
Zeiss 10-in diameter headlamps are fitted, using Bilux bulbs. Dimming is operated by pressure on the inner ring mounted on the steering wheel. Pressure on the opposite side of this ring operates the electric Bosch horn, which also has a duo-tone control switch on the dashboard.
The dashboard is certainly an enthusiast's delight and is strictly functional. The numerous fittings and gauges are as follows, with pride of place to the centrally-mounted huge revolution-counter boldly proclaiming "Undrehungen in der minute". A smaller speedometer which really agrees with the rev-counter and which is converted from kilometres to mph on export models. Oil pressure gauge in kilogrammes per square centimetre, one kg/cm.2 being approximately equivalent to 14 lb/sq in. Oil and water temperature thermometers, Bosch ignition and lighting switch-box, electric clock, pneumatic fuel capacity gauge, reeled self-returning inspection lamp, dual ignition selector switch, dual dashboard lights, Ki-gass pump, petrol tank air pressure priming pump with test gauge, fuel overflow sight glass, choke lever, etc.
Other standard fittings comprise Bosch dual-blade windscreen wiper, trafficators on closed models, driving mirror, cigar-lighter, ashtray, bumpers front and rear, and a tyre inflating air pump with flexible hose supply line mounted on the gearbox on left-hand-drive cars only. The steering wheel is of very large diameter, well notched on the underside and having an inner ring for lamps dimming and horn operation. Mounted in its centre plate are two antennae, the left-hand one for throttle opening setting, the right-hand for ignition timing control. Direction of movement is indicated by zig-zag arrows, black for-throttle, red for ignition, and the plate is surmounted with a large red and black Mercedes badge. An outfit of tools and spare parts was provided in portable cases.
The SSK differs somewhat from the long-chassis SS model.
The suffix K is for kurz or short. The chassis is 1 ft 51/2 in shorter, resulting in a wheelbase of 9 ft 8 in. This was effected behind the mid-length crossmember, bringing the rear wheels well forward. In the driving position the elbow can actually rest on the mudguard. The chassis weight was reduced to 24 cwt, most SSKs being fitted with the stark competition-type body, low-cut sides with no doors, and the passenger's seat set slightly behind the driver's. A short stub hand grip is mounted behind the driver for the passenger's use.
The standard blower was stepped up to deliver at 10 lb/sq in and, with high-compression pistons, the bhp increased to 250. Over 120 mph was obtainable within safe revs. Competition models are fitted with an exhaust cut-out slide valve, and the tyre size increased to 7.00 on the rear wheels. Power-to-weight ratio is 1 to 17 unblown, 1 to 13 blown.
This model was designed specially for competing in hill-climbs such as Mount Ventoux Frieburg, Semmering, Trento, Monte Carlo, etc. It was attended by continuous success, winning the European Hill-Climb Championship in 1930 and 1931. At the 1931 Mount Ventoux Climb Caracciola set a new record for the hill of 15 min 29 sec, averaging 52.4 mph, and in July, 1930, at Shelsley Walsh the same driver set up a new blown sports-car record of 46.8 sec. Both records being gained in the SSK model.
It certainly proved much superior to the SS in cornering on hills and fast road courses and from 1931 onwards was used exclusively in Grand Prix events.
The SSK chassis was also fitted with a drophead coupe body to special order ; mention of these models has already been made, eg, the ex-Rosier car. Only one other remaining SSK with a drophead body is known to be in this country.
The SSK has been aptly described in humorous vein as the largest motor car with the least luggage space.
The SSKL is the short-chassis SSK with a lightened chassis. The suffix L stands for the German word leicht.
This model was the ultimate development of this class or conception of sports car.
The frame was copiously lightened in no half-hearted manner, even the dumb-irons being perforated. The chassis weight was reduced to well under 24 cwt. The SSK engine was highly tuned, embodying a lightened crankshaft, highlift camshaft with special valves, even higher compression ratio, and the famous (or infamous) balanced "Elephant" blower boosting at 12 lb/sq in. The power delivered was close on 300, with a power-to-weight ratio of 1 to 12. Many Grand Prix races were won by this car, which reached a speed of 147 mph on the Avus track, and a grand all-time ultimate for the developed "38/250" engine of 156 mph, in a Mercedes fitted with streamlined body, in the hands of Von Branchitsch at the same track in 1931. In 1932 the same driver obtained the 200-mile record, averaging 121.6 on the Avus track. A superb specimen is preserved to posterity in the Daimler-Benz Aktiengesellschaft Werkn Museum at Stuttgart.
They will live in history as the only production sports car ever to approach the performance of contemporary racing cars.
Performance of SS model
Reverting to the SS, speeds based on the maximum safe rpm of 3,200, 6.50 by 20 in rear tyres, and the 2.5 axle ratio, are theoretically 125 mph, and, using the 2.76 ratio, 112 mph. Speeds in the gears (on 2.76 axle ratio) are : third gear, 93 ; second gear, 62 mph : first gear, 35 mph. Speed at 1,000 rpm : 2.5 axle ratio equals 41 mph, 2.76 axle ratio equals 35 mph.
Power-to-weight ratio is 1 to 18 unblown and 1 to 15 blown. An outstanding feature of the performance of this model is its ability to accelerate in top gear from a mere crawl without snatch or kinking, given judicious use of the ignition control. Advertisement slogans by the manufactiirers clairnea "10 to 110 mph in top gear," which proved justifiable in practice ; the real joy, however, lies in acceleration through the gears combined with an easy cruising speed of 80 mph with the engine turning at a comfortable 2,000 rpm.
A brief period of flat spot can be detected in the power output between approximately 75 to 85 mph in top, but with continued throttle opening the acceleration comes in progressively up to peak revs.
Acceleration figures are : from a standing start to 90 mph in 45 sec ; from 40 to 90 mph in top gear in just over 30 sec ; and from a standing start to 60 mph in 17.9 sec. Brooklands Test hill was climbed in bottom gear in 11.4 sec.
A Brooklands 120-mph certificate is held by Zehender driving a stripped "38/250".
Roadholding is outstanding. Only in severe circumstances is there any tendency to break away on corners. An empty fuel tank can result in slight tail slip but under normal loading cornering can be indulged in at high speed with confidence.
Dependability is all that could be desired. The "38/250" is a sure starter (and in the coldest weather) with a minimum of fuss. It has a regular slow tick-over quite free from oiling-up tendencies, carburation is even, requiring iro choke assistance, and the transmission pulls smoothly without snatch even in the highest gear.
Maintenance and driving
No tuning is required year in, year out, provided standard settings are maintained. The following remarks are offered as points of interest and advice to the owner-driver, many of which, although elementary, are important and have been brought to notice by experience or the model.
(a) The clutch is not the car's best component and must be treated with respect ; 16 to 18 mm free play in the pedal should always be present. Never slip the clutch or hold it out whilst waiting at traffic lights, etc, and always, depress pedal to floorboard. It is advisable to have the plates slotted to relieve distortion.
(b) The Supercharger should not be engaged at low speed nor at near maximum speed. The throttle must be held flat on the floorboard and kept there, slipping of the blower clutch, either when in or in letting out, must be avoided, but a momentary slip when engaging has the advantage of reducing initial shock on the rotors. Ignition should he fully advanced during blowing. Avoid low-gear blowing on wet roads or expect to correct the wheelspin slide.
(c) Keep the brakes regularly adjusted by the handwheels provided. When relining, extreme care is necessary in bedding to suit the drum and it must be done in situ. Brakes should be relined when the thickness is less than .05 inch. The copperised brake drums should never be painted.
(d) A fast tick over is usually caused by the foot throttle linkage sticking ; to slow, kick the throttle down, allowing it to instantly spring back. Normal tick over is 100-150 rpm.
(e) The sparking plug cables from the dual distributor head to the magneto-fired plugs pass through the cylinder block in one bunch. It is advisable to inspect for oil saturation and to replace worn rubber glands where cables thread through the runway below the plugs. Connections to distributor head should be very carefully attached with no stray strands.
(f) Constantly observe water pump warning window and keep pressure on hand greaser cup.
(g) Shock-absorbers should be regulated on the hard side.
(h) Engine oil should be always topped up to the maximum level of the three-way tap. Never allow to get down to minimum.
(i) With air-pressure fuel system release blow-off tap under dashboard when pressure builds up to 3 lb/sq in. Safety blow-off valve embodied in the air pump or the filler cap may be blocked. This needs watching with a full tank.
(j) Full retard when starting reduces risk of damage to starter motor by the severe high-compression kick back.
(k) Special solid cylinder head gaskets cannot be used owing to a projecting lip on the cylinder liners.
It is-beyond the scope of this article to attempt to describe procedure in tackling major maintenance operations such as decarbonisation, clutch withdrawal, etc., which require skilled specialist attention. Few present-day owner-drivers will possess the heavy tackle necessary or the special tools, for certain operations, which were originally supplied with the car.
Lastly, it should be kept constantly in mind that one is travelling much faster than realised. The change from the everyday run-about to a slow-revving, high-chassis car of this type can be very deceptive, particularly when coming up behind slow traffic. It is then that full appreciation is realised of what it takes to stop two tons at veloeity X without servo or any other assistance !
A long series of successes were achieved by the "38/250," the extent of which has never received full appreciation in this country.
These successes of the big six-cylinder Mercedes started with the "36/220" Model S which came in first, second and third in the German GP in 1927 and 1928.
"Scrap" Thistlethwaite is considered to be the first to demonstrate the "38/250" to the British public, which he did to good effect by winning the 1929 Southport "100," defeating the wellknown supercharged Vauxhall Villiers. Some doubt exists, however, whether the car then used was a new SS model or the S model which he drove in the 1928 Irish TT, achieving fastest lap of 74.39 mph. Information from readers possessing contemporary reports of the 1929 Southport "100" would be appreciated. The successes of the "38/250" year by year may be tabulated as under ;-
1929; German GP, 3rd (Momberger). Irish TT, 1st (Caracciola); fastest lap, 77.81 mph, in Class II, average speed 72.8 mph. Defeated team of three blower "41/2" Bentleys. Monaco GP, (Caracciola), SSK. Monza GP, 3rd (Momberger); 1st in first beat, winning from a 16-cylinder Maserati. Irish GP—Fastest lap was by Thistlethwayte, 53.8 mph retired with blown gasket. Southport "100", 1st (Thistlethwaite).
1930; Monaco GP, 3rd, Monaco SSK model. Mille Miglia, 1st (Caracciola and Werner), SSK. Avus, 1st (Caracciola), averaged 119 mph over 163 miles, maximum speed 147 mph. Irish TT, Highest average speed of 71.53 mph was by Sir Malcolm Campbell, driving the famous GP10. Fastest lap was by Earl Howe of 77.2 mph driving the 1929 winning car acquired from Caracclola, UW 302. Irish GP, 1st (Caracciola), SSK, Lap record of 93.3 mph and averaged 85.88, attaining 137 mph, beating Bentley team. 3rd (Earl Howe), SS, 1929 Irish TT winning car. Hill-Climb Championship of Europe, Ist. (SSK)
Before proceeding, mention should be made of the widely-held conception that an intense rivalry existed between the official Bentley and Mercedes teams, whereas in actual fact they met in only three international events, namely, 1929 Irish TT, 1930 Irish GP, and 1930 Le Mans race. Of these, Mercedes won the first two races and Bentley the third. Over-confidence in only entering one car at Le Mans against six Bentley "entries" cost Mercedes their one and only failure in international competition with the Bentley marque.
1931: Avus.-1st. (Von Brauchitsch). SSKL: average speed 121 mph; maximum speed 156 mph. 3rd (Caracciola), SSK; average speed 115.39 mph. German GP.- 1st (Caracciola) SSK. Belgian 24-Hour Race.-lst (Prince Djordzadze and Zehender), SS. Circuit of Llow.-Ist (Von Stuck), SS. Eifel Racs.--lst (Caracciola), SSKL. 3rd (Von Brauchitsch). Mille Miglia -1st (Caracciola and Sebastian), SSK; 1,001 miles in 16 hrs 10 min. Argentine National GP.-1st (Zatuszcek), SSK. Argentine GP.- 1st (Zatuszcek) SSK. Geneva GP.- 2nd (Cathsch). Le Mans.-2nd (Stoffel and Ivanovsky) SSK, lap record 87.27 mph. Czecho-Slovak GP.---2nd (Von Stuck), SSK. Irish GP.--5th (Earl Howe), SS. lap record 91.8 mph, beating Caracciola's 1930 lap record of 91.3 mph. Hill-Climb Championship of Europe.-1stt (Caracciola), 5 wins.
1932; Mille Miglia.- 1st (Caracciola) driving an SSK, put up a lap record of 70 mph.
Returning to appearances of the "38/250" in this country, we find that between 1929 and 1932 a few appeared frequently at Brooklands but, although always spectacular, they did not have the consistency in private hands of the "works" tuned cars. Amongst the more interesting of Brooklands meetings, entries were as follows;- 1931 Whitsun BARC Mountain Speed Chamionship, Won by Sir Malcolm Campbell driving an SS model at 64.8 mph. Autumn BARC.-Earl Howe lapped at 118.3 mph in the ex-Caracciola TT car. September Mountain Speed Handicap.--Sir Malcolm Campbell lapped at 71.39 mph, while Earl Howe's' best lap was 68.81 mph. (He lapped the outer circuit at 118.3 mph).
1931; Whitsun BARC Second Mountain Speed Handicap.--Sir M Campbell broke the lap record at 73.89 mph, finishing third. Autumn BARC Second Mountain Speed Handicap.--Cambell's best lap was 72.13 mph, finishing second. October.-120 mph badge certificate won by Zehender.
1932: JCC 1,000-Mile Race.-Staniland lapped at 113 and 97 mph despite having blown up his engine in practice and rebuilding. Sir M Campbell, on an SS (GP10), threw ablazing tyre.
In many of the lesser races held at Brooklanda private owners often had the misfortune to retire due to either blowing the cylinder-head gasket or to supercharger faults. It must be admitted that the "38/250" has carried in the enthusiast's mind these labels to this day, and in addition to being voracious consumers of tyres due to the weight combined with high bhp, the initial cost debarred the acquisition of such a car, except to the very wealthy. These then are the chief reasons why the "38/250" did not appear to be a popular choice with the leading drivers of those days despite their unassailable international reputation.
The racing record of the "38/250" will not be complete without reference to its appearances at British hill-climbs. In September, 1929, it made its first appearance, at Shelsley Walsh, when Earl Howe, driving the ex-Caracciola TT car, registered 47.6 sec, which was very creditable on the long-chassis model. At this meeting Thistlethwaite also entered an SS and scored 49.6 sec.
In July, 1930, Caracciola set up a new sports-car record for Shelsley of 40.84 sec, and at the same meeting Jack Dunfee, driving the Hon Dorothy Paget's car, went up in 50.4 sec. In 1931, Earl Howe clocked 46.8 sec, improving this in 1934 to 46.2 sec which remains the best time up Shelsley by a "38/250" Mercedes.
It will be of interest to Bentley enthusiasts to compare with the foregoing Forrest Lycett's best time at Shelsley in the famous 8-litre of 44.08 sec, which without the kick from a big supercharger is a most impressive feat of sheer driving skill.
In these present times of vintage-car enthusiasm a few notable examples of the "38/'250" can still be seen in action. The best known of these has been Lefty Crozier's immaculate black drephead coupe on the SSK chassis, which contributed elegance to our beloved Prescott meetings and was impeccably handled, but, alas, will be seen no more on this side of the Atlantic.
Earl Howe's original "86/220," now owned. for many years by HE Rohll with its beautiful sleek maroon two-seater body and torpedo running-boards, is also a well-known competitor.
Another present-day entrant which is considered to be the only authentic German team car in this country is N Powell's silver two-seater SSK with left-hand drive. Its exact racing history is obscure but it is reputed to be one of the ex-Caracciola cars used in Continental events and first brought to this country in 1935, when it was owned by that great Mercedes enthusiast D Conan Doyle, and later by Sir R Gunther.
Other examples include a "38/250" driven by D Storr, which in the 1951 BDC Silverstone Invitation Race came in third behind the 8-litre Barnato Hassan and Tony Hartridge's Speed Six Bentley.
Brighton Speed Trial spectators will be familiar with Mrs Lee Kennard's white competition-bodied two-seater on the SS chassis. This car was tuned by the late R Arbuthnot and has high-compression pistons and the 2.5 axle ratio. It is probably the most powerful sports car to be seen handled by a lady driver in post-war meetings and was previously owned by the author.
The ex-Dorothy Paget four-seater tourer has turned up and is now owned by G Haft, whilst the blue SSK, ex-Roy Lewis has changed hands recently. Of the famous examples well known in prewar days only the ex-Roy Eccles maroon two-seater SS remains untraced. The famous ex-Sir M Campbell white SSfour-seater, GP10, is still in this country.
The "38/250" is now becoming a rare specimen of the high-performance vintage sports car. It is almost certain that a few were scrapped during the war, which accounts partially for their non-reappearance in the numbers we were accustomed to seeing. Let us hope that the remainder are still laid up awaiting liberation when the injustice of the horse-power tax anomaly is corrected. Strangely enough there have been no reports from tourists or correspondents of any examples having been seen on the Continent. It is ironic to contemplate that the country of origin was guilty of their extinction as scrap metal !
Trying to assess how many cars of this model were manufactured is a matter of speculation, owing to the chassis numbers being allocated in a continuous sequence over a range of concurrent models, including the "83/180" and "30/220." A range of chassis numbers has been observed implying an output of over 3,000. This is not a very large output considering it was spread over the years 1928-1931 and possibly included four different models, but lacking the official figures it can only be regarded as an assumption. The writer has kept a record of all models known to be in existence at the present time. In addition, three S models and three SS have been fitted with diesel engines in this country.
The above figures represent a mere residue of the total production, and are far from complete.
This narrative has been confined to the model, above all others, which has given colour to the saga of Mercedes. Greater heights of fame were to be achieved later with the scintillating successes of the pukka GP racing cars. Sleeker and more luxurious supercharged Mercedes production models took the limelight of the world's salons, but to the true sportsman of those days nothing can ever take the place or attain the appeal of those full-blooded, deep-throated super-sports supercharged "38/250s."
At the 1939 Berlin Motor Show a new model was displayed called the 580K, which, owing to the war, never went into production. A maximum speed of 140 mph was claimed and, as Mercedes have always been conservative over published performance figures, this would have been the world's fastest production car.
A resurgence of that inborn genius of Gottlieb Daimler and Karl Benz for automobile design is now in process on the drawing-boards at Stuttgart-Unterturkheim. New models have been shown bearing the indefinable stamp of pedigree, with each new revelation the pulse beats faster, rumours of mystery Grand Prix cars in preparation once more stir the imagination—the three-pointed star is in the ascendant. The toast of International motor sport, as it was in the beginning, may be again, Hoch die Mercedes.