Massive bang on quick gear change

[93URS4Avant]

I get a knock sometimes - I wouldn't go as far as calling it a BANG - its diff-mounts. Possibly by upgrading all of the other components it has exacerbated them?

[K Simmonds]

I get a bang from the rear of my 3B S2 on fast gear changes under load, every bush ect is polyurethane or solid alloy so I'm 99% sure it's too much back lash in the diff combined with the solid polyurethane rear diff mount that's the cause.

I have a spare diff that I'm going to rebuild and I may go back to a brand new OEM rear diff mount, I'll see what it behaves like with a rebuilt diff before trying a standard rear mount.

[Error404]

Prop bearing is fine and aligned properly
I have sorted the bang in the rear as I said above - that was too backlash in my V8diff, which I will adjust
I have the diff rebuild PDFs if you need them Kit - word of warning there are tons of special tools required to rebuild the pinion shaft and bearings. I have managed to lay my hands on the proper VAG tool for driving in the outer bearing races for the diff casing which you need to do to redistribute the bearing shims to adjust the backlash if that might help at some point


My problem now as I said above that i can't think if a reason for still having a massive drivetrain lurch when I come on and off the throttle - it only happens in 1st, 2nd and 3rd and a bit in 4th gear - and only at low rpm. I also get a whine from gearbox backing off the loud pedal above 6k rpm in 2nd and 3rd gear, as it winds down, all of this makes me think this is the weak 5 speed in the CQ as never heard S2 owners complaining about this?

[K Simmonds]

Ahh, I see. Just read through the previous page of posts properly.

Thanks for the heads up on rebuilding the diff, not as straight forward as I expected. I do have the paper Bently manual for the CQ ect, think the procedure is covered in detail in there will have a look latter, though from what you've said I may just change the seals in my spare diff as they need doing anyway and bang it straight in on a gamble hoping it cures the problem as it pises me off as well. As far as I can tell the 3B S2 shares its gearbox prop and diff with the 20V CQ.

Regarding the lurching, you could be onto something with the worn gear box theory. Now you have such a solid set up any play will manifest itself through the body of the car as opposed to being lost in sloppy mounts and bushes. I don't get any lurching with mine at all, the gearbox itself is very smooth (thank god) so I'm pretty sure I only have to contend with the diff.

[93URS4Avant]

ahhhhh - penny drops!

[Error404]

Kit the 01A in the CQ is different to the 3B (much shorter gearing) and I'm sure the 3B box is reinforced

I've got an 01E in the man-cave but really can't be bothered to fit it to test out my theory at the moment - maybe a job for the summer