The Truth about the Jeep

By Capt. John Moon

Many people are wondering what will happen if conventional trials cars have to meet the Jeep in future competitions. In this informative article Capt. J. S. Moon, of the S.E. Asia Command, gives his candid opinion of the Jeep after long personal experience of this vehicle we all know so well by sight.—Ed.

A correspondent to one of the motoring weeklies has asserted that the Jeep provides the complete answer to those who have stated that America could not produce a sports car. This, of course, is not true, as the Jeep is far from being a sports car, unless one defines a sports car as a car that gives one pleasure to drive, a definition that is much too broad to be of any use, since it covers any car driven by an enthusiast during war-time. Nevertheless, I think that a few notes on the Jeep as seen by a motoring enthusiast may be of interest to those readers of MOTOR SPORT who have not had first-hand experience of this fascinating little vehicle.

As the story of the origin of the Jeep has been the subject of litigation in the U.S.A., it must be treated rather cautiously. However, I believe that the original idea for a general purpose four-wheel-drive light car came from the American War Department and the Bantam Motor Co. The latter, it will be remembered, were the successors to American Austin Co., producing the Bantam, an Americanised-version of the Austin Seven. The original Jeep was not a complete success, partly because its weight gave insufficient adhesion for towing. Revised versions, produced by Willys and Ford, as well as Bantam, were more successful and were put into large-scale production. For some reason, the Ford and Bantam versions were dropped after the initial batches, but Willys continued large-scale production, and the Willys version was also produced by Ford in very large quantities as the Ford G.P.W., which is identical in every respect with the Willys M.B.

Another point that I do not intend to enlarge upon is whether the car, 5 cwt., 4 by 4, to give it its British Army nomenclature, should be called a “Jeep” or a “Peep,” as quite enough has been written about that already! I can, however, give two more names (polite) that I have heard. The first is “Bantam,” which is of obvious origin. The second, “Dingo,” is more obscure, but arises from the fact that in the Middle East Jeeps were at one time used in the same role as Daimler Scout cars, which were commonly known as “Dingos,” obviously having been christened by the Australians.

All my experience has been with the Willys M.B., or the identical Ford G.P.W. Of the earlier Ford G.P. I only know that it had a rather larger engine and was externally recognisable by a different radiator grille, a normal type hand-brake lever, and a rectangular panel combining all the instruments. A very few of these were produced as four-wheel-steering jobs, with a front axle at both ends.

A few notes on the Jeep’s specification will not be out of place, but to avoid masses of figures in the text I have given the principal dimensions and such performance figures as are available in a data panel.

The Jeep engine is very similar to the pre-war Willys Overland private car unit, and is a perfectly orthodox side-valve, downdraught-carburetted 4-cylinder, whose performance is in no way remarkable for these days. It has two points of some interest: the camshaft drive is by silent inverted-tooth chain, a design feature that I thought had been completely relegated to the past, and the oil pump consists of one internal and one external gear. Finally, the quick-release latch on the dynamo mounting enables the belt tension to be slackened for fording.

The engine is mounted, offset slightly to the left in unit with the three-speed-and-reverse synchromesh gearbox, on flexible mountings, the underneath of the whole unit being protected from damage by rocks by a stout steel plate — quite a trials feature. The drive is taken through a single-plate clutch of orthodox design, the spring not being of the diaphragm type that features on most modern American vehicles. Behind the main gearbox, and an integral part of the engine/gearbox unit, is mounted the auxiliary gearbox. Through this the drive is taken downwards and to the right through either a train of single helical gears, giving no reduction in ratio, or through straight spur gears giving a reduction of 1.97 to 1, thus providing the alternative high and low ranges of gear ratios. At the front end of the driven shaft of the auxiliary box is a dog clutch which engages the optional front drive. Two additional short gear levers to the right of the main lever engage, respectively, the front drive and the low range of gears, an interlock being arranged so that the low range can only be engaged when all four wheels are being driven. On the rear end of the final drive shaft is the external contracting parking brake, operated through a heavy Bowden cable from an umbrella-handle lever on the dashboard.

From the auxiliary box the drive passes through needle-roller-jointed shafts to the hypoid bevels and pinions of the front and rear axles, the final drive assemblies being offset to the right in the casings. At first it is rather surprising to find that the rear axle is of the fully-floating variety, but one soon realises that this construction is adopted so that the hubs and bearings are interchangeable front and rear. The front axle, of course, incorporates constant-velocity universal joints to accommodate the steering movement, these joints being of one of three types, Tracta, Rzeppa or Bendix. The stub axles pivot in the axle casing in tapered roller bearings.

The steering gear, a Ross cam and twin-pin lever variety, is mounted on the left side of the frame, but is the opposite way round to normal, i.e., has the drop arm on the inside of the frame member. Motion is transmitted forward by the push-and-pull rod to a bell crank pivoted approximately in the centre of the axle, and thence by two separate tie rods to forwardly projecting steering arms on each stub axle.

The foot-brake operates expanding shoes in 9-in, diameter drums on all road wheels through a normal Lockheed fluid system.

Suspension at all four corners is by quite flexible semi-elliptic springs mounted on threaded U-type shackles. There is an extra torque spring under the left-hand spring to stabilise the axle under braking. Damping is by adjustable, direct-acting hydraulic shock-absorbers, which are both reliable and effective. The frame has deep channel-section sides and five cross-members with diagonal bracing at the rear. When seen in a stripped condition the frame looks as though it were from a very much larger vehicle.

Petrol is carried in an L-sectioned tank under the driver’s seat, and contains about 12 1/2 imperial gallons. On later Models it is filled through a very large diameter orifice with a pull-out tube, but the early Jeeps had a very small hole through which it was difficult to refuel.

Electrical equipment is 6-volt, with constant-voltage current regulation. The lighting arrangements are rather complicated, being designed to operate under either blackout or normal conditions. As the blackout is now a thing of the past as regards the majority of readers, I do not propose to describe in detail the nine lights provided, nor how various combinations of them are operated by the push-pull switch on the dash. It is worth mentioning that the main headlamps are of the sealed beam variety and are very effective, and that the small lamps mounted under them, known as blackout headlamps, give a polarised beam which cannot be seen above the horizontal. There are two dashlamps, and, presumably for blackout reasons, no ignition warning lamp. The starter switch is foot-operated.

Instruments are of the excellent type common to all American service vehicles, and almost come up to the best European sports-car standards as regards legibility — a complete change from American private-car practice. They are all in separate circular dials with white figuring on a black background, the speedo. needle being luminous. They comprise a 60 m.p.h. speedometer, oil pressure gauge, vapour pressure-operated thermometer, electric fuel gauge and ammeter. Minor controls, apart from the three switches and the hand-brake, are piano wire pullout controls for the choke and the throttle. The right-hand side of the dash is occupied by a useful locker with a plunger-type catch for the lid.

The engine compartment is covered by a lid hinged at the rear. Lifting this reveals the radiator, with cowled fan, battery, headlamps, voltage control and oil and petrol filters, as well as the engine itself, so that quite a large space is completely filled.

The body is, of course, purely utilitarian, and provides about as much weather protection as most motor-cycles. The hood, which removes and folds up under the front passenger’s seat, is apparently designed to keep the sun off, to provide as much draught as possible for the backs of all the occupants’ necks, and to remind the driver when he is going too fast by flapping on the top of his head. A better pen than mine is needed to describe the hardness of the cushions after a day’s journey. The windscreen arrangement is very practical. The screen will open upwards in the normal manner to a horizontal position, or the complete frame will fold forward to lie fiat on the bonnet top. A hand-operated wiper only is provided — a cause of much annoyance in wet weather.

One of the interesting features about a Jeep, and one which governs the body design to some extent, is that by removing the windscreens these vehicles can be stacked one on top of another, the front wheels resting on the flat front wings of the underneath one, and the rear wheels on the wheel arches. As regards performance, a plate on the dashboard gives the speeds shown in the data panel as maxima which are not to be exceeded, and these do represent speeds above which the engine begins to feel overstressed. The maximum speed I put at just under, rather than over, 65 m.p.h. but some Jeeps are much better than others. Before leaving England, I had meant to time my Jeep over a standing quarter-mile and from 0 to 50 m.p.h., in order to get some definite indication of the acceleration, but like many good intentions, it was not carried out. Actually, while undoubtedly good, I do not think that figures would prove as outstanding as many people suppose. I think a lot of the apparent snap of the Jeep on the road is due to the high bottom gear, which enables it to get up to 25 m.p.h. while other cars are having their gears changed.

The gear ratios are quite well chosen for a three-speed box, though bottom gear always seems to me to be rather high. Careful clutch engagement is necessary, and with a full load, and most certainly when towing, any upgrade makes “low-low ” desirable for restarting. Any abuse of the clutch leads to early failure, as this component is not very large and seems to have a rather low safety, factor. Apart from this, the clutch is smooth and well behaved.

The main gearbox synchromesh, as in many cars, tends to get tired rather early in life, so that double declutching downwards is desirable, and upwards results in a slightly quicker change than the alternative. Clutchless changes go through quite nicely in spite of the synchro. The gear lever is not too long and is rather more rigid than those of some American cars. Gear changes in the auxiliary box go through easily by double declutching, but are slow, due to the large change in ratio. Front-wheel drive is engaged and disengaged without stopping, but is sometimes difficult to disengage when one axle gets wound up relative to the other and causes the dogs to bind.

Roadholding I class as fair (by sportscar standards). It is aided by the fairly considerable weight, but is influenced far more in the other direction by the very considerable unsprung weight of the live front axle. The centre of gravity must be quite low because of the absence of a roof and of the fairly low engine mounting, although the ground clearance is very good and the seating position is high. Rolling, therefore, is not too pronounced in spite of the soft springs.

The foot-brake is up to the usual Lockheed standard in power, but braking hard from anything over 45 m.p.h. produces quite a fierce swerve to the left, due to the front axle winding up on the springs and thus pulling on the push-and-pull rod. This twisting takes place in spite of the torque reaction spring on the left-hand side. This swerving, with an oversteering tendency, can make stopping in a hurry an interesting process.

The hand-brake is purely a parking brake, and its use while on the move produces transmission judder. It needs watching rather carefully, as it sometimes sticks on or fails to free properly, while some drivers have been known to drive away with it on — to its rapid detriment. I am rather in favour of its pull-out control, on which the ratchet is released by partial rotation of the handle from the straight-down position. This is quite easily accomplished with one finger, giving a fly-off effect. Apart from this, a transmission brake always makes for easier starting on hills.

Steering is fairly accurate, quite light and, by American standards, high geared, requiring about 2 1/2 turns from lock to lock, with an excellent turning circle.

The exhaust note is pleasantly audible, but not loud, unless the rather thin exhaust pipe or silencer have rusted through.

Petrol consumption varies with driving conditions, but to exceed 18 m.p.g. on main roads is rare, which cannot be classed as a brilliant performance from a 2.2-litre car weighing just over a ton.

The cross-country performance of the Jeep with four-wheel drive engaged is, of course, terrific, far exceeding that of any two-wheel-drive vehicle. Short of gluey mud or soft sand over axle level, there is nowhere where it can set its four wheels that a Jeep cannot go.

A question that is looming in some people’s minds is what will be the effect on post-war trials of large numbers of Jeep entries (assuming, that is, that Jeeps are available to the general public). Personally, I think that in trials of pre-war severity, where final results are often determined by special tests, the Allard and the ” Grasshopper ” Austin would wipe up a standard Jeep nine times out of ten, due to the latter’s inferior power/weight ratio. Of course, if trials are stiffened up to the standard of pre-war German events, the Jeep will have a great advantage over a two-wheel-driven vehicle.

Can the Jeep power/weight ratio be improved by simple modification? I doubt it. The weight of a Jeep is inherent in the design and is not built in to any particular component that could be discarded or extensively lightened. Moreover, supposing that one could pare off a couple of hundredweight, which brings the weight down to something comparable with the Allard in trials form, one has to consider the deleterious effect upon the already not-too-good roadholding of increasing the unsprung weight ratio, since the axles could not be lightened in proportion to the rest of the vehicle.

What about increasing the power output ? Again difficult, I think. While much can be done by increasing the compression ratio and the valve overlap and using re-designed manifolds with twin carburetters, the only way to make 2.2 litres compare with 3.6 is to super-charge, a process of which I think the engine would not approve. In any case, any appreciable increase in power would necessitate a larger clutch, and probably gearbox modifications as well. The solution may be found by someone who can install a Mercury V8 engine and mate it up with the Jeep transmission. Until then, I do not think that the “Tailwaggers” and the “Grasshoppers” need lose overmuch sleep over the prospect of hordes of Jeeps participating in post-war trials.

It may be added, in conclusion, that the apparent impracticability of improving the Jeep by modifying it is a further proof of the excellence of its design, as the essence of design is to achieve the best possible compromise between opposing factors, and it certainly appears that this has been attained in the Jeep.

Data Sheet

Car, cwt., 4 by 4, Willys M.B. or Ford G.P.W.


No. of Cylinders … 4

Bore … 3 1/8 in. (79.4mm)

Stroke … 4 3/8 in. (111.1mm)

Cubic Capacity … 132.4cu. in. (2,201cc)

R.A.C. Rating … 15.6hp

Stroke/Bore Ratio … 1.40-1

Compression Ratio … 6.48-1

Maximum Power Output … 60b.h.p. at 4,000r.p.m.

Specific Output … 27.3 h.p. per litre

B.M.E.P. at Max. Power … 88.4 lb. per

Maximum Torque … 105 ft.-lb. at 2,000 r.p.m.

Maximum B.M.E.P. … 118.0 lb. per

Maximum Engine Speed … 4,000 r.p.m.

Maximum Piston Speed … 2,920 ft. per min.

Gear Ratios

Top … High Range – 4.88 Low Range – 9.6

Second … High Range – 7.62 Low Range – 15.0

Low … High Range – 12.8 Low Range – 25.2

Reverse… High Range – 17.3 Low Range – 34.1

Maximum Speeds (corresponding to 4000 r.p.m.)

Top … High Range – 65 m.p.h Low Range – 33 m.p.h

Top … High Range – 41 m.p.h Low Range – 21 m.p.h.

Top … High Range – 24 m.p.h Low Range – 12 m.p.h.

Top … High Range – 18 m.p.h Low Range – 9 m.p.h.


Wheelbase … 80 in.

Track … 48 1/4 in.

Overall Length … 132 1/4 in.

Overall Width … 62 in.

Overall Height (to top of windscreen) … 63 in.

Weight (ready for road) … 2,315 lb.

Weight (fully laden) … 3,125 lb.