One of the 'improvements I promised myself to make on my 1938 Traction Avant Slough Roadster is the 4 speed conversion as offered by Roger Williams of Steamcar developments. I will also put modern C/V drive shafts in the car and a diaphragm clutch. I know to some this may sound as a heresy and will rule this car out from many 'concours d'elegance', but I promise to keep the original power plant and gearbox intact for future owners, whishing to go back to the 'original'.
Coincidentally, two articles have recently appeared in 'Floating power' and 'La Traction Avant' about the subject of 4 speed conversion. The advantages it brings, the difficulty or ease of performing this upgrade etc. I will use a few quotes from these articles. See Issue Dec/Jan 2002 of 'Floating power' and Issue 50 of 'Traction Avant'.
Any Citroën aficionado knows the story about the exploding automatic gearboxes of the early Traction Avant prototypes and how a new manual gearbox had to be hurriedly introduced. The quoted articles mention some of the weaknesses in the design, like the taper roller bearings, weak aluminum caps holding them and poor synchromesh action. I for one have experienced this weakness first hand, when one of my early Tractions split open her gearbox on an Amsterdam Tramway crossing! The same article mentions the replacement 4speed box virtually indestructable.
The 'Traction Avant' article describes this as a task that a well trained mechanic apparently can do in a day. I had seen this conversion as an item or 'kit' obtainable from Steamcar Developments: 'price on request', usually the description of something that is not for the faint hearted or shallow pocketed. I have now witnessed this conversion twice in the Wood Lane workshop of Roger Williams and can assure you that doing this 'right' involves a lot more than a day's work, although I have heard of botched up jobs where people have taken a sledge hammer approach to knock certain bits of the front suspension into shape to create the extra bit of space where required. I decided to also put in the much lighter and more powerful ID19 engine. The restoration of this engine will be the subject of another web page. I drew the line at putting in the cross flow cylinder head of the ID19, which I find ugly and out of place under a Traction bonnet. Replacing this with an 11D head is a good compromise, which to the untrained eye makes it hard to 'spot the difference' with an original Perfo engine.
3 sets of ID 4 speed gearboxes waiting for conversion into a Traction.
While the basic shape of the 4 speed ID gearbox is the same as for the 3 speed Traction Avant, some modifications are necessary to mount the assembly in a Traction engine bay. The following picture clearly shows the parts manufactured by Steamcar Developments. Then the operating assembly under the dashboard is replaced. Part of the Tractions front assembly cross member is cut away, necessitating some welding to reinforce it in places at the same time. The side engine mountings are replaced with that of and ID engine and the rear silent block gets a new mounting. This re-engineering has the net effect of setting the ID19 engine further back so that the drive shafts don't foul on the front suspension as would be the case on a one day 'botch job'.
New Gearbox suspension unit from Steamcar Developments.
New command mechanism to operate the 4 speed gearbox
Spending a day in Roger's workshop soon re-enforces the impression that a passion for quality is paramount in his work. An impressive array of bore gauges and micrometers was used to check everything to the finest tolerances. If something like the end float of a gear on the pinion shaft, was not quite right, it was soon corrected by putting one of the thrust washers back in the surface grinder to take it to the required specifications.
New rear silent-block mounting unit
See
a movie of the finished product.
Warning 5.6 MB file!!
The gear operating mechanism is shown just below the output flange. The arm will need to be bent and chromed like a Traction's
Page last update November 3rd, 2002
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