Reconditioning the gearbox in my 1955 Traction.

Richard Sheil

Dublin, Ireland

Introduction:

As some of our members may know my car broke down fairly significantly at the 2006 TOC Annual Rally in York which necessitated an engine rebuild. However I had noticed that the gearbox had become rather noisy and so decided to recondition it too during the winter of 2006 / 2007.

Having never done this before to any car I began to realise that there was a fair bit of mystery attached to the Traction gearbox and set about understanding what was required. These notes are a description of what I did to my gearbox and I am sure more experienced people may have some other views. They also don’t describe every action but are written from the point of view of what I would have liked to have known before starting out on this project.

The manual that I have is very clear in listing each step of activity required. What it lacks is a clear overview of what the steps are trying to achieve. Without the overview I think you are operating blind.


 

Objective:

In my view the objective of the gearbox overhaul is to replace all bearings and bushes, inspect and replace gears and shafts etc as necessary and to set clearances to specification.

I have modified the drawings from the parts books to reference the numbers that are used in the manual. This made it easier to ensure that the correct parts were reinstalled correctly and to understand what is going on.

 

Having disassembled the gearbox to its constituent parts and having cleaned them and laid them out in order on the bench the objectives are:

Disassembly:

Disassembly of the gearbox is relatively straightforward if the manual is followed. In my case I discovered the following. I broke the casting supporting the reverse gear idler shaft as I tried to drive the shaft out with a punch. If I had extracted the plug which inhibits removal of this shaft by pushing it in toward the gearbox this would not have happened. I also found all gears to be in excellent condition. The differential had large play caused by the crown wheel not being properly fixed to the differential housing and by significant wear in the planet / satellite gear area. Given that I was going to reset everything to factory settings I did not measure the existing settings but others may wish to do so for completeness. The large nuts on the end of each shaft were removed using a large socket. To do this the gearbox must be stopped from rotating and this is done by selecting 3rd and 1st gear at the same time.

Replacement:

I replaced all the bearings in the box. The only quirk worth noting is that the rear bearings for the primary shaft were not available and instead of replacing two bearings with a spacer between them, a single bearing was used, held in place with circlips. In my case I had to grind down one of the circlips by a small amount to allow both clips return into their associated grooves in the shaft.

I replaced all the bronze bushings in the gears as they were allowing each gear to rock slightly in relation to the shaft. I replaced bushings in gears 18, 35, 40 and the reverse / first idler. A hydraulic press is needed to carry this out and the bushing in gear 18 had to have oil holes drilled once installed. The bushing in gear 35 consists of two bushings which are pressed in from each end. I understand that they can have a tendency to migrate towards the centre of the gear so I installed them with Loctite Bearing Fit.

Reassembly of the Differential:

This was quite fiddly as it was necessary to repeatedly trial fit each satellite pinion and washer to the cross shafts in the differential to determine the correct washer thickness for each satellite pinion (see Differential drawing). Once this was done the whole differential was then reassembled repeatedly  with different thickness celeron washers behind the planet gears to until minimum backlash but no binding was achieved. In my case the satellite pinion washers were not available in the thickness that I required so I compensated for this by increasing the thickness of the washers behind the pinions to tighten the mesh.

I used new bolts to clamp the crown wheel to the differential housing and fastened them with lock tabs and Loctite.

Setting axial clearances on shafts:

Parts 34 to 21 were reinstalled on the primary shaft and held in place with the locking pin and spring that can be seen on the Gears drawing. This was done with the shaft removed from the gearbox. The pin and spring were reinstalled using some grease to stop them flying across the workshop and a bent piece of wire to push them home. I used a pop rivet with the end bent at 90 degrees to make a think hook. The thickness of the washer 36 (made of fibre like material called Celeron) was chosen to make the required clearance as listed above. In my case having bought washers in myriad sizes I still did not have what I required so had to adjust the thickness of the washer by rubbing it on a flat surface with emery paper. Once again this was a case of multiple trial fittings until a suitable clearance was obtained.

The third gear axial play was checked between 3 and 38 and found to be acceptable. If it was not then the steel washer 38 would have had to be ground to size.

The pinion shaft was also assembled on the bench and when fully tightened the clearance between 39 and the bearing checked. I am confident that the part listed as 51 (see Gears Drawing) does not exist on late gearboxes. Once again the celeron washer 39 had to be made to the required thickness on the emery paper.

I measured the reverse / first idler play. It was more than the specification but as I had no means to change it and as the bearing races and hardened washers had no evidence of wear I deemed the settings not to have changed since the gearbox was first built. On consideration I was confident that this was one of the least important clearances in the box and reassembled it unadjusted.


Reassembly:

The pinion shaft was then disassembled and reassembled into the gearbox casing. The differential was reinstalled to the casing with the ring nuts tightened fully (see Differential drawing) so that there could be no wobble of the differential housing relative to the casing. In my case the number etched on the pinion and crown wheel was 56.70mm. Given that the diameter of the housing is 55 mm this indicates a clearance of 1.70mm between the end of the pinion and the housing. This was then set by means of multiple trial fittings of punched metal shims between the bearing housing and the gearbox casing. I did not install the cover over the bearing housing and discovered to my disappointment that the pinion could move towards the front of the box thus making all my work void. I then repeated the task with the cover on the housing to achieve the correct clearance.

Once that setting was completed the differential was removed and the reverse and primary shafts reinstalled in the box. The reverse shaft was refitted before the primary shaft. The primary shaft was installed paying particular attention that the synchro key (37) was engaged firmly between washers 34 and 38. If this was not done correctly it would chew itself to bits in moments. Apparently this is a common failure mode of these boxes if the nut on the end of the primary shaft becomes loose. I used Loctite on both nuts on the end of both shafts to reduce the chances of this happening. I also tightened the nuts as tight as I could using an extension bar on the socket drive and a wooden pole wedged into the gearbox housing to provide leverage.

Once all gears were reinstalled the differential was refitted. The axial clearance was rechecked.

The ring nuts on each side of the tapered differential bearings were adjusted successively so as to bring the crown wheel into mesh with the pinion. A dial indicator was then used to check that the free rotation of the crown wheel was between 0.19 to 0.23mm at the outer diameter of the crown wheel. This was done with the pinion stopped from rotating by a block of wood so that the movement was purely the play between the meshing teeth at the pinion to crown-wheel.

Once this was achieved the ring nuts were backed off slightly to allow the play required by the tapered bearings. 

With all of these settings rechecked the top cover of the gearbox was reinstalled temporarily. The selectors were activated so that third gear was selected. The cover was then removed and it was determined that the synchromesh unit overlapped the teeth of third gear. This same test was repeated for second gear. With the unit overlapping third gear when pushed forward and second gear when pushed rearwards I was confident that the axial location of the primary shaft was acceptable. There is a more complex procedure in the manual but after careful consideration I was confident that this was enough. 

Testing:

I reinstalled the box in the car together with the newly rebuilt engine and took the car for a drive. Sounds easy! Once I got over my fears that the whole thing would grind to a halt I was amazed at the difference in feel. The gear change was more positive and while it is early days I am confident that the overall noise level and howling from the differential are much reduced. It just feels a whole lot more pleasant to use.

Conclusion:

I would recommend anybody with some mechanical experience and the limited special tools (dial indicator and feeler gauges) to take this on. You won’t regret it.

 

Finally I would like to thank the people on the TA-L discussion group as they were a wonderful sounding board for me and provided guidance every step of the way.

This article has been reproduced with full permission of the author


Last update: 05 Dec 2007 Contact us

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