Kiwi Landie said:

Hi all.

Onto the gearbox rebuild now in my 1976 S3 with suffix B box. I have reassembled it all, and mated it with the bellhousing. Now at this point the manual says "check that the mainshaft and layshaft rotate freely with minimal endfloat.

The layshaft is fine. Once I tightened up the front bolt I could feel the slightest bit of endfloat on the shaft, which I reckon is good enough. The mainshaft is a different beast entirely. Going by the book, there should be minimal endfloat BEFORE I put the oil thrower, rearmost mainshaft gear, shims and the horrible castellated locknut on the back. On mine with these components missing I have about 3 mm of endfloat on the mainshaft. Doesn't make sense to me. Surely there is nothing to prevent endfloat UNTIL those components are in place and the devil nut is done up nice and tight. My shaft is a snug fit in the rear bearing, but not super tight, hence the float.

Can someone please set me right here? I am worried that I have missed something out, but I have checked against the various parts diagrams and I have definitely got everything in the gearbox that should be there. I am missing the shim washer 501501 and tab washer 217476 on the outside which prevent my tightening the rear lock nut up completely, so I cannot say for sure at the moment whether doing that will remove the endfloat. My pick is that it will. A second opinion would be great!

Thanks guys.
Andrew

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Kiwi Landie said:

OK - So I reassembled the front cover on the gearbox and put the nut on the back of the mainshaft. I'm running a RoamerDrive, so there's a big carrier bush thing that goes on the tail end of the mainshaft instead of the normal gear. Primary pinion is all sitting nicely with a new circlip and spacer bush, with next to zero endfloat.

Working outwards from the back end oil seal, I now have the oil flinger/spacer piece, then the RoamerDrive carrier bush, then the nut. Tightened it all up and still got a bit of float on the mainshaft. I made up a shim which sits inside the carrier bush and the float has gone away. Everything turns nicely and looking down into the box, all the pairs of gears are exactly aligned. So far so good.

Now I find that there is considerable end float on the 3/4 synchro unit at the front end of the mainshaft. Everything else is locked down real good, but that is now the only component not truly secured and it can slide about 3 mm back and forth along the mainshaft. If I engage the central slider it goes into place in either direction with a good positive action on the springs and stays put. I engaged 4th and reverse together to lock the box and allow me to tighten the layshaft and mainshaft nuts to 65 and 85 lbft respectively and nothing was showing any signs of moving or disengaging.

So - now my question is, when the gearbox is assembled to this stage (ie complete, minus the selectors), and there is essentially no float on either the layshaft or the mainshafts themselves, and the gears are nicely lining up with each other, should I see this amount of movement in the 3/4 synchro, and if not, what can I do about it? There doesn't seem to be any option to shim it out, as there is nowhere for the shims to go. Forwards there is the primary pinion and backwards is 3rd gear. The only way I could see that I've come unstuck with what I have done is if my thrust washer that sits on the bottom of the mainshaft next to the first gear synchro unit is massively too thin. That would explain why I still had a bit of mainshaft endfloat even with the RoamerDrive nut in place. It would also go some way to explaining the float on the 3/4 synchro. But we'd need it to be about 3 mm too thin and it didn't look too bad to me when it went in. That'd be a huge discrepancy. Also if that thrust washer was that much thicker, it'd push the gear pairs out of alignment with each other.

Anyone got any ideas? Should the 3/4 synchro slide about like that?

Cheers
Andrew

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