DHC’s gearbox rebuild part 3

The last update on the rebuilt of the new gearbox for the DHC (at least I hope so). With the measurements to determine the necessary shim thickness for the main shaft done, the long wait for the shims to arrived began. In the end I decided it might be a good idea to contact the chaps at S&S to see if they could supply the correct thickness shims, which they couldn't. But they were able to supply some oversize thickness shims in. So I could machine them down to the correct thickness. This together with some 0.05 mm steel sheets, enabled me to adjust the main and lay shaft end float properly. In the end it turned out that the thickest off the supplied shims for the main shaft was spot on and the lay shaft needed an extra shim of 0.05 mm to get it spot on.

With the front of the gear box finished I could switch my attention to the rear of the ‘box. Fitting the fifth gear assembly to the main shaft showed me that this also needed an extra 0.05 mm shim to get the end float within the required tolerances. After which fitting the fifth gear selector fork and spool was the proverbial piece of cake ...

Left me with the rear casing, fitting the various seals and oil pump. Turned out that the old O-ring that came out was rather skinny compared to the new one. Explains why there was a small oil leak through the selector shafts hole. But that should be well and truly solved now with the double seal.

But before fitting the rear casing to the gear boxes centre plate it seemed like a good idea to trial fit it, just to be sure. Glad I did it as it turned out that the drive shaft supplied with the new oil pump was incorrect (to long), as a result of which the rear casing just wouldn't fit properly. Luckily the old one that came out was in perfect condition so that was re-used. And with the correct drive shaft in place the rear casing slipped on as it should.

And with the speedo drive gear, rear bearing, oil seal and flange fitted the box now is nearly ready to be fitted to the car. But as it stands now that will have to wait till after my holiday and the International Auto Ecosse.

What went wrong?

With the paint job on the DHC finished and the car slowly but surely being assembled, it is time to look back and see what went wrong with the paint.

The best solution we can come up with (and backed up by a few people who should know) points to the remains of the chemicals used for stripping the paint as the main cause for the problems. But why did it take almost two years for the discolouration to show?  This is almost certainly down to the fact that the car was out in the rain for a prolonged period waiting for recovery in Austria after the break down on the Timmelsjoch during the 10CR. This triggered the remaining chemicals to react with the water based paint causing the discolouration. The car was actually soaking wet inside and outside when it was returned from Austria.

So we followed the advice of the paint manufacturer Sikkens, and opted for a two pack paint. This kind of paint is officially forbidden in the Netherlands (due to health & safety issues) but may be used for specialist jobs. As a result of which it's only available on special order. Luckily we still had the old recipe to get a few litres of paint made. Added bonus of this paint is that its application is much easier, giving a better finish, as a result of which polishing out any blemishes is greatly reduced compared with the original paint job. Downside is that the paint alone cost nearly as much as the complete paintjob (including all preparations) during the restoration a few years ago!

And as usually in such cases the company that did the paint removal for Giessen (Mitraco in Belgium) wash their hands in innocence. Or as they say "In the 25 years that we use this process we never had any problems". Strange than, that a representative from a supplier who walked into the workshop, and after looking at the paint discolouration, only asked if the paint stripping had been done in Belgium? But worst of all is the fact that Mitraco even refuse to answer a few normal questions regarding the chemicals they use. Needless to say we won’t use them for future projects.

In the meantime I have been able to work on the car on and off and hopefully it will be fully re-assembled within the next few weeks. Leaving only the gearbox to be replaced by the one I am still rebuilding. Well actually I haven’t done much to it over the past weeks because I have been waiting for shims for almost two months now. Luckily S&S preparations managed to sent some over which where to thick but I was able to have them machined down a bit. But as the gearbox is at home and my tools are in the shed, finishing the gearbox will have to wait a few more days.