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MG MGB Technical - Rear end clunk

I replaced my wire wheel axle with a steel wheel one earlier this year and replaced the shims before I fitted it. The crown wheel and pinion surfaces didn't look too bad. I'm now getting some rear end clunk on occasion. I thought it was coming from the offside rear wheel but now I have the roof up I can hear it is coming from the diff area. It could of course be the UJ and I will change that anyway but was wondering if just changing the shims in the diff would remove any clunk from that area. Is there any way to determine if the clunk is from the diff or the UJ (apart from changing the UJ of course).
Steve Church

When does it happen? The clunk could be play in the diff. Probably the thrust washers. A rough measurement of diff play is:-
With the car safely supported, go underneath and grasp the rearmost end of the prop shaft. Turn it fully right (or left - it doesn't matter). Mark the prop flange and also the adjacent rim of the diff "nose" (i.e the pinion seal cover) so that the marks are aligned. Fully turn the the prop the other way and make another mark on the pinion seal cover in alignment with the mark already on the prop. You now have one mark on the prop and 2 marks on the pinion seal cover. Measure the gap between the 2 marks on the pinion seal cover. If the gap is any more than about 5 or 6 mm you'll probably need to renew the thrust washers. The bigger the gap the louder the clunk!
Have you checked engine/gearbox mounts, axle U-bolts,(they might just need re-tightening if you swapped axles) shackles, exhaust mounts etc? Check again after you've replaced the UJs - it could be the cumulative effect of small amounts of wear in several parts. Do the U-bolt nuts first - it's a no-cost job. Oh, such fun.
C J Carroll

I get the clunk when changing gear. Also if I ease off then accelerate again. Not all the time but most of it. I replaced the thrust washers before I put the axle on. I have had problems with the U bolts not being tight enough (exhibited by torque steer) so will check them before anything else. The diff play should be easy enough to check also. All the rear suspension fixings have been redone recently as I replaced the bushes with polybushes.
I'll recheck the tightnes of those too. Thanks for the advice.
Steve Church

I had a similar clunk on my B roadster and changed UJs then fitted an anticlonk kit in the diff. Turned out to be the exhaust downpipe sometimes making chassis contact because the bracket had come loose. Embarrassing or what? Trust me tho' - it really did sound like a drive train clunk.
I've just finished a total resto of the drive train & rear suspension on my V8 using blue polys. I've had to re-tighten the new U-bolts 3 times now.. I've changed the nylocs to full nuts to get a decent torque on them. They are now at 25 ft lbs - couldn't get past 20 with nylocs. Result.
C J Carroll

I fitted blue polybushes all round too...Superpro I think. I've tightened up the U bolts twice so maybe time to do it again.
Steve Church

Do not overtighten the U bolts. If you get torque steer, do check that the sheet metal piece on the axle by the U bolt is not cracked.
werner haussmann

Hub to half-shaft splines can move and make a noise as well, although in theory they are supposed to be locked together with the taper.

I don't understand what is meant by not being able to get past 20 ftlb with Nylocs, Nylocs should torque up sooner, but still not clamp the axle to spring as tightly as plain nuts do. I also had to retighten the U-bolts several times, it's par for the course as the pads compress further over time. I've never torqued them, just done them up until the gradual tightening becomes rapid tightening.
PaulH Solihull

This thread was discussed between 09/09/2011 and 12/09/2011

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