A virtual magazine for a true passion!

Editor: Jaap Horst

Volume 2, Issue 4
The engine of the T37 (and also of the T40). Admission side

Detailing details

Author: Jaap Horst

A few weeks ago I went to visit my friend Ton van de Roer, also in the Netherlands. He is in the process of building his own Bugatti (T37). And when I say building his own, I mean it! Every part is carefully made, to original specifications, and he showed me various of these.

Nice detail is that he began making miniatures, and no average miniatures either! He built a working T55, including engine. Here everything works, brakes, suspension, steering, engine (though a 4-cylinder, because of scale-effects). He also built a 6 cylinder d.o.c. truely Bugatti-type engine, which does fit in the T55 chassis. And this all is in 1/5 scale. When this was finished, a friend of his asked him, if he could make all parts for the miniature, why not build a full-scale Bugatti??

During my talks with him he showed and told me various strange and sometimes funny technical details of Bugatti (especially the T37, but most of the technicallities also are the same for the other models). So this will be a truely in-depth technical article. People who are interested in Bugattis for aesthetics only better click your "back" button. Or better still, do read on and get involved with the aspects of Bugattis, which one can normally only enjoy when owning or working on Bugattis!


Ettore, known to have said that he made his cars to go, not stop, did do quite some good work on the part of brakes. Incorporating for example the brake drums in the wheels, as is the case for all aluminium wheels of eg. the T35 onwards, ensured good cooling of the brakes, and easy accessibility. It was possible to change brake shoes during the race!

These brake shoes have a danger though. The friction force on one of the brake shoes tends to increase the braking force, let's say the brake works harder then one wants it to. This can even lead to blocking of the brake, but at low speeds only. When this happens the brake back plate, of metal plate only (at least in the T35/37), shears of at the holes for the mounting bolts, leaving one with no (front) brakes! This can be overcome by removing part of the brake shoe lining, actually making the total surface to brake with smaller.

Also, he was early in introducing hydraulic brakes, already on the T28 prototype and on some T30's. However, the system didn't work reliably, Ettore did away with it and invented the best ever all-mechanical brakes. The brakes all are cable-operated, but equalising mechanisms ensure that the braking force on all the wheels is the same, also if the wear of all the brakes isn't

When other companies like Lockheed later on offered more reliable hydraulic brake systems, Ettore still wouldn't accept them, and continued to use his mechanical brakes until late in the 1930's, but by then it was Jean who actually was responsable for the automobile design.


The clutch is operated through a special devise working with four little levers to pressurise the clutch plates. Ettore invented it when he was still working for Deutz, and used it ever since. (well, I do not know if it was still there in the T57) It has some peculiarities though. Because the levers rotate with the shaft, centrifugal forces work on them. Actually it is more the centrifugal force than the springs who pressurise the clutch plates. Effect of this is that one needs more force to press the clutch pedal at high (engine) speeds, than at low ones.

A second peculiarity of the system is that, when the levers are not well adjusted, they can pass the most extreme position that is still alowed. The effect? The clutch remains disengaged! Remedy? Press the clutch pedal! This time the effect of the clutch pedal has inverted, the pedal must be pressed to engage the clutch, and released to de-clutch!

Front axle

Everybody, I hope, knows about the famous Bugatti front axle, hollow in the middle, tapered towards the ends, and with the holes for the leafsprings going through them. They really are the hallmark of Bugatti suspension engineering. It will take too much to explain here exactly how these were made, but it is possible, Ton van de Roer has made quite a few. He had one, and let me handle it, it weighs only 10 kg! And the piece of metal one begins with to make it, is 120 kg!

Steering unit

All Bugattis have their steering working the same way, with a worm and wheel. The worm is turned with the steering wheel, the wheel is connected to a lever, and through the steering arm to the front wheels. So far nothing strange. However, the movement of the lever is limited, therefore less than half the circumference of the wheel is used, The wheel is complete though, teeth all around it. Ah! Perfect, after the wheel has worn on one side, one can turn it round, and continue using the other half? No, wrong answer. The hole for the lever is tapered, it is impossible to use the other half! Here some weight might have been saved!


Especially at the beginning, castings were not perfect at Molsheim. (and possibly not with any other foundry either) The cylindre blocks of for example the T37 had waterways around the spark plug holes, to assure cooling. The bottom side of these was only some 3 - 4 mm wide, and was prone to fill up during casting of the metal. Once it was known this happened, this was checked with a tiny mirror! If waterways were blocked, holes were bored from both sides of the block, through the length of the block, not an easy task either! Finally a plug was inserted, to block the hole off to the outside, which still is a way to recognise an early from a later cylindre block.

Not only blocks were casted, of course, and lots of castings like covers etc. were made of aluminium. Here also, apart from a high percentage of castings being discarded because of too grave errors, sometimes repairs were made. In case of a small hole in a casting, a "star plug" was driven into the metal, to block of the hole. After finishing it can be hardly seen. Only the metal of the plug is different from the casting, making it shine in a slightly different way! Please do not go inspecting all bugatti cam-covers etcetera now though!

With special thanks to Ton van de Roer!

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