Bilstein: gas-damping expertise reaps a reward
“OF COURSE, it’s got Bilsteins on it…” That dismissive statement, one that forms a normal part of the British enthusiast’s dialogue and has even led to the formation of companies with German-sounding names to emphasise quality, prompted our curiosity recently. Bilstein gas pressure shock-absorbers, originally developed by the West German concern as one of seven worldwide de Carbon licence holders, are now a feature that is taken for granted on the autobahns, race circuits and rally tracks of the world. How did they gain such an enviable reputation and become such a part of our motoring lives? And why do they not contest Grand Prix, where Koni now rule the roost?
In short, who are Bilstein?
MOTOR SPORT travelled to the picturesque town of Ennepetal, about an hour by autobahn outside Cologne, to answer these questions. In a small office overlooking the original 1873 foundry, we renewed our acquaintance with long time manager of Bilstein’s press and sports programmes, Hugo Emde. In the afternoon we had the privilege of meeting managing director Dr. Petzsch, who effectively runs the fashionably diversified Bilstein factories, though there are still female descendants of August Bilstein (1847-1915) with active interest in the performance of the company today.
The Ennepetal works were the site for a company primarily involved in making interior metal fittings for houses and factories, particularly metal fittings for windows. The First World War led to a natural expansion of metal pressing and manufacturing skills, some acquired in munitions production. However it was August’s son Hans who faced the tricky task of managing his father’s now multi-skilled company through the inflation-stricken Twenties period of German history and the Thirties, which were daunting not only for the worldwide recession, but also for the dictator’s Nazi policies, which made an impact on Bilstein between 1933-45, just as they did on the rest of the world.
However, the company that steered through these dangerous reefs successfully was now a recognised part of the automotive component industry. By the Thirties Bilstein had emerged as manufacturers not only of household fittings, but also as makers of car bumpers, wheeled lifts for garage work and car jacking equipment.
Today garage equipment like the hydraulic jacks and cranes of all types are an important 20 per cent of the business, which also covers window fittings (30 per cent) as well as dampers, which Herr Emde reckoned accounted for 50 per cent of the company’s 1979 turnover of 130,000,000 Dm. (approximately £30.2 million).
However, the shock-absorbers really divide into a number of separate stories themselves. Mass production — over 1,000 units in an order by Bilstein’s definition — takes place only at the modern Mandern factory. Employing 950 people and all the benefits of construction from scratch (in 1956). Mandern produces all the window fittings for which Bilstein are also known inside the industry, as well as the large shock-absorber runs for customers like Ford, who use Bilstein damping on the Granada, Capri S and the new Escort XR3. In talking of Mandern one senses how Bilstein have protected themselves against a fall off in business in any particular area. For example Emde told us “VW are small-run customers on the shock-absorber business with Bilstein, but very big customers for jacks.” If you don’t succeed in one area, there’s always another avenue to try from the Bilstein salesman’s viewpoint.
The sites we visited were all concentrated around the town of Ennepetal, our particular interest drawn by the two-storey August Bilstein Werk III, factory. Crouched down beside the railway lines and attendant crossing a short car ride away from August Bilstein Strasse, this modest building houses the limited production run damper business, a separate competition department, a busy experimental division and all the attendant quality control sections that we found to be almost an obsession within the building.
Learning principles into practice . . .
A Lufthansa world map on one wall and souvenir pictures, mainly of competition over the years, looked down from the walls of that compact Ennepetal office as Hugo Emde recalled Bilstein’s early struggles with the French Professor de Carbon’s gas-pressurised telescopic shock-absorbers.
In this connection it is important to realise straight away that a Bilstein damper is not just filled with pressurised gas; a Bilstein is constructed on a single tube principle, that tube divided into an upper and lower chamber. However the lower chamber (the one closest to the bottom mounting point) is filled with nitrogen at a pressure — depending on application — of around 350 psi. A dividing piston seals the gas chamber off from the working piston and conventional piston sliding rod, which is surrounding by an hydraulic light oil — again in a number of varieties (viscosities and additives) to suit the application.
The principles in the increasingly popular strut applications of Bilstein pressurised damping are similar, but with one extremely important variation. The piston rod does not slide up and down. It is fixed upside down to the floor of the strut with the oil and gas unit above, and a top use of bearings to absorb lateral forces. The shock-absorber tube is thus working on a large bearing surface which allows vertical movement as well as a better absorption of side forces.
Emde recalled Bilstein’s experiences with the de Carbon system during the years after the July 1st 1954 granting of licence to build dampers along these principles. “I think de Carbon had tried to sell his ideas everywhere without too much success. For ourselves, we had three years of problems trying to seal the dampers properly. Right to ’57 we had these terrible problems…” He laughed weakly in mock exasperation of the Teutonic mind trying impose perfection upon an unruly but brilliant Gallic principle. Outright laughter as he said, “the bloody things were leaking oil as they were produced from our factory to be transported to the train!
“Then we find an answer. It is in the sealing, a double sealing ring, which prevents all these leakage troubles and is effective to 240’c. In fact we still use this kind of double sealing ring today, though the new Golf and Erika Escort sports model have a new Teflon ring system.”
Production of Bilsteins with the double sealing system was effective in 1958. Interesting to note that it was Mercedes who were the first customers in what Emde succinctly describes as “the Adenauer-type saloon, the bigger 300 type”. That was in 1958 and that year Bilstein made 3,000 gas dampers: ten years later they were making 150,000 such units a year!
Emde remembered, “At first it was all the bigger type Mercedes that were using our dampers . . . particularly the 190/220 and the 220S of that series, but by 1961 we were on all Mercedes. Of course they are bigger cars anyway, so our product was very good for them, making all the difference in damping out vibrations that can reach through a suspension system. Our gas system allows the designer to make hard bushes to control the suspension properly, but without the harshness because the gas damping helps absorb that compared with a normal damper. This has worked well for Ford and Mercedes independent rear suspension systems, and it can be a big help, even on a live axle use like the Capri.”
The writer understands that the mass production system of Bilsteins offered on Capri S, or as the rear damping on lesser Capris, is not the complete answer. Experience with the limited production Bilsteins and low profile tyre combination from Pirelli (P6 and P7) leads the author to summarise that the improvement between a Bilstein built to a mass production price and one constructed at a slower pace with increased damping capacity, offers the same large improvement as replacing worn conventional shock-absorbers with a good sporting damper. It is possible to offer a Capri with ride and handling that we simply would not have believed of the original 3-litre Ford. However, there is a non-VAT (15 per cent) price of £180 quoted by Ford just for the front struts and rear dampers on the Bilstein-equipped demonstrator, MHN 710V, that gave rise to those complimentary comments.
Bilstein’s original equipment business developed gradually. That other Stuttgart prestige manufacturer, Porsche, were the next customers and the Swedes were not slow on the uptake either with both Volvo and SAAB taking an early interest.
However, it was once again Mercedes who led Bilstein into new areas as Emde told us, “in 1959 the factory decided to endurance run a 190 D diesel saloon from Stuttgart to Johannesburg, so this was our first competition customer! As Mercedes did various long rallies — like in Argentina for example and then winning the European Rally Championship twice [Walter Schock in 1960 and Eugen Bohringer two years later — J.W.) so we became involved.”
Emde was similarly involved from the start. He and his wife are the hosts at the fully equipped Bilstein mobile competition works that operate from a converted coach-style body, a familiar sight at so many European race tracks during the season, and an integral part of the German Championship.
“At first we were just using slightly modified production dampers. Our first official year was 1960 in competition and that’s when the 220 SEb was the car for Mercedes. Later we had SAAB and Volvo along with their rallying cars and DKW’s little two-strokes along for racing. You remember those fantastic little cars? They were so quick! When Porsche went into 1 1/2-litre Formula One (1961) we went with them and so it went on building and building. . . .”
By 1965 Porsche were converted to Bilstein for all their sports racing machinery and this was obviously a significant step for Bilstein as Weissach developed from class contenders into a dominating power in Seventies sports car events. Emde was particularly proud to record their involvement in the 1,000 b.h.p. plus Can Am Porsche 917 developments, where Mark Donohue’s efforts made the world’s most powerful circuit racing car an entirely manageable beast. America became a routine stop for Emde in addition to his roving role in Europe, where French had been added to English and some Italian to help in his ambassadorial/sporting managerial role.
Historically speaking there were two extremely important milestones in the Iate Sixties and early Seventies. In 1967 Mercedes decided that they needed more dampers than Bilstein could countenance building — there always has been a marked and understandable reluctance for Bilstein to put too many of their corporate eggs just in the shock-absorbing basket of their activities. Thus Bilstein found that they needed to promote their sporting image to attract new custom. Emde’s personal interests and those of the company coincided and increased effort was put into supplying works teams, especially in rallying. “A shock-absorber is not a glamour part, so we have to show it works better by competition,” says Emde summarising their sports commitment.
It was here the links with Ford grew, particularly with the advent of the Escort and a World Championship programme that included the East African Safari Rally. Such an event demanded a special shock-absorber, capable of operating at very high temperatures and loads. As routine Ford expected very strong strut casings with the traditional wedging that is so vital for a MacPherson strut to live over 100 m.p.h. jumps. The Safari also led Bilstein into the production of competition dampers with alloy casings to disperse heat (and offer a worthwhile weight advantage over steel) and the use of 25% Molykote to ensure that the piston/tube lubrication shield is maintained even at extraordinary temperatures and loadings.
The 1970 milestone was tragic. August Bilstein was killed virtually on the premises when a car hit him in January 1970, leaving only his wife and daughter (who still live in the town) directly involved in the company, which has been managed by non-family professionals ever since.
By the time we had absorbed so much information and spent an informal lunch half hour primarily discussing why Bilstein were not in Formula One, the factory “walkabout” became a sprint against the departure time of our airplane from Cologne! Incidentally the reasoning for not being in Formula One seemed much like Porsche “the engineering information from touring car and rallying competitions is much more useful to us than racing in Formula One. I like Formula One personally and I know many of the people, but for the company Grand Prix is about a little bit show-business rather than business-business,” said Emde with a chuckle.
We spent our time on tour largely devoted to Werk III and its contents. Entering by a top gallery and looking down on the masses of steel tubing being joined by their precision-made internals struck an oddly familiar note. The way of working and the obvious age of the the buildings (basically add-on facilities to the original Twenties’ structure), rather than the super-white clinical approach, immediately reminded one of a Midlands car components company.
Regretfully we have to say that there the British comparison ends. Once on the shop floor the quick interchange of comment between Emde as a member of senior management and everyone working the machines, or those supervising them, served as a reminder that it is not so much the machinery and environment that matter when trying to reproduce quality on a production line, as the mutual respect of the human beings employed for each other. About 600 people work at the factories and administration centres spread around Ennepetal, but the atmosphere was that of a British company employing somewhere between 16-60 staff: informal but generally efficient. It is not a miracle or a selection of wonder workers who produce results for some magical reason in West Germany, just hard graft and knowledge of both product and customers.
Some of the key facts to emerge centred upon those piston seals. The double seal that achieved reliable performance for Bilstein is composed of a Viton and Permbunan ring located by steel and alloy plates, like the rest of the damper largely made by Bilstein. In fact the machine that inserts the oil at a constant 20 degrees C and the one that inserts the chamber dividing sealing rings/piston was developed by Bilstein as well.
I gather that most of the machines needed for this specialist work were developed by the company, obviously including a lot of test apparatus. Checks l saw included those for bump and rebound to 7 1/2 per cent tolerances and a selection of eagle-eyed ladies with large magnifying glass quizzing tube casing thickness and piston rod quality. On casing thickness I was told two out of every fifty pieces are checked while each piston rod has to be checked for its chrome plating of induction hardened steel with a tensile strength of “over ten tons”. That plating is real precision work, to a tolerance of .0002 mm. thickness. However, those standards have to be reached and the reject rate is 10-20 per cent as routines on this item and 5-8 per cent on piston seals.
The stores carry about 4,500 different shock-absorber parts for the limited production Bilstein range, an average of about 60 components per unit.
Static rigs are also employed for a great deal of quality control or development testing. A typical test I saw involved a new Escort damper with the rebound stop inside the damper itself undergoing 20,000 cycles of rebound operation check with an 11 lb. or so load. That is nothing compared with a routine 1 million cycles in other tests.
Dampers are also checked for operation in sub-zero climates. Pretty well everywhere you look in the test department a machine is torturing a damper or strut — sometimes it will prove to be one made by Koni or another rival. No, I’m not going to repeat what Bilstein said about their rivals, I’m sure they’d say the same things about Bilstein!
It was interesting to find that Bilstein now find themselves in something of a Michelin situation where everyone is doing their best to produce a competitive version of their product — Boge and Monroe were examples cited, but they are far from the only ones who have decided that the gas pressure system can offer protection against oil foaming within, and a stability of ride, plus durability qualities that a straightforward twin tube conventional damper does not match. It was also pointed out that another reason “it is impossible to match our product” is the patented grease used to keep those sealing rings sliding and sealing.
A detailed look at a Porsche 3.3 turbo front strut showed the kind of thinking that is necessary when supplying the manufacturers of a 160 m.p.h. car. “Here we will use a 40 mm. thick casing, instead of 30 mm. for something like a VW, and this improves the steering a lot at the high cornering forces a Porsche can reach. There is also a reserve chamber of grease just to make sure lubrication is maintained at these kind of loads — and also three internal bump stops are necessary,” said Hugo. A lot of this expertise obviously came from their racing experience to judge by expert books relating to damper development on the 911.
Incidentally the factory numbering system covers type, the fourth figure covers setting and then a fabrication number of up to seven figures. This allows them to tell on which day and on which machine the damper was made, helping swift rectification of any faults that do arise.
On most of the units you see offered for retail sale, finish will be in the company yellow and contain a steel tubing case. Racing and some rally applications may have a threaded ride height adjustment casing in either steel or alloy, while Mercedes (again!) are now taking some of the lightweight aluminium cased Bilsteins with an Aachen specialist electro-coating. This gives a matt plastic look to the finish and makes the case as rigid as steel, without the weight penalty.
On the original equipment side some new internally sprung, Teflon-seal, dampers were being produced for BMW’s 3-series and there was a lot of background work going on to improve the range of applications for the new Escort/Golf seals. Research seems to be pretty constant into oil grades that can be used — Esso alone supply four grades with additivies that cater in varying degrees for a quiet ride and other damping characteristics — and the variety of gas pressures that can be used to modify damping.
What is the difference between production Bilsteins and racing units? Emde answered, “the main changes are in the settings — we can take care to make it suitable for the application, the type of course, the damper will meet and in the changes we can make to get absolutely the best performance. A few years later and these ideas can be in production . . . Like competition made us put alloy cases on, thread the casings, wedge the struts, try new oils, and additives, and save 50 per cent on weight. In racing we are maybe a little bit in the hands of the driver, but with somebody like Klaus Ludwig in the Turbo Capri in Hockenheim we can say exactly what is needed to give more or less understeer/oversteer at a particular place, or to stop the car weaving if there has been a change in tyres or conditions. We get so much information from a man like Ludwig that it is easy to make progress, but some of the others . . .” Emde throws his hands up while naming some prominent names who got to the top with heart, not science! There is a machine to run the dampers through a simulated dry lap of Nurburgring, but recent Mercedes rally results show machines cannot substitute for competition experience completely!
It’s only a small department — perhaps 30 people in all on the competition side, but since 1972 they have produced about 120,000 competition dampers including some 50,000 MacPherson strut types. When I called there was a lot of orders on hand from Australia, not only from the GM Holden outfit but also from the Frank Gardner-managed BMW turbo racing project (ex-McLaren USA) Emde commented that he is still in almost daily contact with the Australian veteran who dominated British touring car events for so long with a variety of Fords and Chevrolets.
Other customers were a typically varied bunch from Polonez, Opel and Ford factory efforts, through to Mercedes for their rally cars, some development material for Audi’s Quattro four-wheel drive (I got the impression that rival equipment was being primarily used at this stage of development for the turbo Audi), to Porsche. Then there were privateer operations like Super Vee customers, Hans Heyer’s German Championship Lancia Montecarlo turbo and Dave Brodie’s Capri. Once the parts are all to hand each until will probably require in the region of six hours’ hand assembly work.
Development tends to be at the factory of the manufacturer concerned, followed by possible general sales later. So there is no Bilstein test track — though you could fairly say it was anywhere in the world where these now a Bilstein products are used — J.W.