GTV6 Driveline Vibration after Reassembly

[Fylnn]

I had the GTV back on the road after a major rebuild into a rally car.  I had the driveshaft rebuilt and balanced as part of that.  Anyway once back together the first time it was sweet as a nut.  Sadly, it wasn't to stay that way, as there was a substantial oil leak out of the rear main seals on the side of the bearing block.  So the engine had to come out, and it has all been fixed and good.

But problem now is that since putting it all back together there is a vibration at around 3,500 rpm.  Pretty sure it was not there before.  Now I carefully marked everything along the way and pretty sure it all went back together in the same orientations.  While it was all apart this time I took the opportunity to change the front transmission mounts, and the rear engine mount in the little bell housing.  Anyone got any bright ideas how to diagnose and fix?

I did a few searches and found some posts about the transmission mounts most likely being from a 75 so they might be a different height or something.  I also found a few posts about lossening off the yoke bolts, the centre mount bolts and the front pinch bolt and 'give it a rev' to let things settle down.  That seems a bit extreme.  Not sure if there are ways to check the alighnment of the whole thing.

Anyway any ideas gratefully accepted. 

[aggie57]

The only way I have heard to check the alignment after installation is with a chassis jig, which Beninca's down here in Melbourne have I believe but not sure if someone up your way would have the same thing. 

One of the common reasons for problems like this after assembly is that the small locating spigots in the centre of the doughnuts haven't seated correctly. If everything else looks OK then I'd certainly be checking that not just to fix the vibration but also to avoid damaging the tail shaft.

[Fylnn]

Thanks for the suggestions, i am not 100% sure of whether there were spacers or not on the gearbox mounts as i had a friend do that bit.  I did also have trouble gettting the rear yoke back together, long story, but it was on then off and might have got twisted.  I am sort of leaning towards undoing it all and retightening in the order described as a first step, then if that doesn't help go to the gearbox mounts. 

[Fylnn]

Well looks like the mystery has been solved.  When I dropped out the cross member and transaxle it became obvious that the new transaxle mounts had an extra spacer plate welded under them.  They were from IAP in the USA, and the plate itself is about 4-5mm, but when it has been welded it has distorted slightly and all up adds about 7-8mm.  So the tailshaft is about that much too high at the rear end.

Anyway, pulled them out, ground off the welds and removed the plates, reassembled and immediately noticed how much easier the tailshaft was to put into the guibo.  All bolts went straight in by hand and all that.  Now car revs cleanly again, no vibration.

So my success rate with IAP parts is about 50%, going back to local guys I think.