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MG MGB Technical - Do I have 'the clunk'?

My B (1980 roadster, rostyle wheels) has always given a good jerk when I accellerate quickly. I noticed, while I was replacing my rear wheel cylinders that the rear hub, partiularly on the driver's side is free to spin a few degreese before "caching" and providing the minimal resistance that would come from spinning the axle and all the gears and wheels in the differential. So there's slack in my rear hubs. This explains the jolt/noise that I get when I hit the gas. I've read many posts about the typical rear end clunk. All mention the noise but I didn't see any mention of the actual jolt or of slack/free play in the rear hubs. So are these symptoms of the "clunk" or possibly of other problems? I'm a little aprehensive about doing the whole thrust washer fix procedure....Thanks.
Brian

Don't worry it's just a little play in your diff. IMHO I'd just leave it until it got intolerably noisy (a long way off). VERY unlikely to be play in the hubs ?????
Stuart Robson

Well, by just grabbing one of the wheel studs I can actually rotate the hub about 10 or so degreese forward and back before I feel it "catch" and begin to turn the axle. Makes for jerky driving when starting from a stop or when shifting quickly. Just wondering if the traditional rear end clunk was just a noise or was accompanied by play in hubs and jerky starts?
Brian

Get under the car (well supported of course) with the parking brake firmly on and try twisting the drive shaft. There should be little or no free play. On mine I could move it back and forwards several degrees accompanied by clonking in the diff. Changing the thrust washers cured it completely.

Mike
Mike Howlett

Changing the thrust washers or whatever they are called, is quite an easy job, bit smelly with the oil, but you can easy do it in an afternoon. Make sure you clean the outside of the diff so that no dirt falls in your eyes or the diff itself. I did not disconnect the brake line on the hub, only moved it to one side and supported it. Order the 4 new washers, gasket and oil, gasket sealer for the large gasket, and its sorted for another ten years.


Tatty ( Non-member since 2003 )

Tatty

I had a clunk on letting out the clutch and when I let off the gas. It turned out to be a bad down link on the rear shock. The bolt in the upper link was broken and twisting in the rubber brush on the down link. Check out the condition of the brushs on the springs, down links and u-bolts. Worn u-joints on the drive shaft can also cause a clunk. Thrust washers are not the only cause.
Jim Lema

Between getting the diff thrusts done and replacing the rear springs and bushes I got rid of a lot of clunks on my car.

Simon
Simon Jansen

Per mike's instructions. Jacked up car, put stands all around. I can turn the drive shaft some (way more than seems healthy) with the rear wheels fixed by the handbrake. Similarly, with the handbrake off, I can turn either rear wheel about as much before the drive shaft begins to turn. Noting that my car has new rear leafs and u-bolts I assume this points to thrust washers. Porter's book speaks to this but made it sound a bit daunting with the removal of the half shafts and all. Others have suggested that replacing them is pretty easy. I've never opened up a diff before, seems like a pandora's box. Any tips to share?
Brian

Brian, The half shafts do need to be pulled out far enough to clear the differential side gears. Unless the wheel seals have recently been replaced this is a good time to replace them. Pulling the half shafts will require some kind of puller or some innovation like using an old brake drum on backwards and pounding the shafts out. You'll need to remove the backing plates to access the bearing retainers. Some pinion pins come out with little effort but some can be a real bear to remove. If you drive the pinion pin to far toward the front and cannot turn the differential your problems will get bigger. Not trying to discourage you, but it can be a problem if some care isn't exercised. I believe Gordon Strickland at The B hive has made up kits for this service, making it easy to get the correct parts. http://www.thebhive.com/index.html
Good luck, Clifton
Clifton Gordon

Brian,
As the others have said, this a fairly simple job and there are some pretty good instructions out there. It's much easier with the differential on a workbench and the diff may come out of its housing on its own. The instruction book says you need an axle stretcher to remove the diff, but 3 out of 4 rear ends I've rebuilt have had the diff just lift out and the 4th lifted out with minor encouragement from a small prybar. If you do remove the diff, and I wouldn't reccommend it unless you're having some sort of big problem, keep very careful track of the bearing caps and the spacer 'washer'/shims on the outside of the carrier bearings. You need to reinstall them so the bearing caps are facing the right way and the shims are on the same side they came out of. That's how the ring gear will end up in the same spot it was before and you don't mess up the backlash (how the ring and pinion gears mesh). If you reinstall the same parts the way they came out and don't change the bearings (odds are they're fine anyway) things stay the same in there except for your new thrust washers. Oh, and don't be alarmed by the lack of a fiber washer when you first look in there - I haven't found an old one in any of the rear ends I've opened up. They disintegrate!
Safety Fast, Wade
Wade Keene

You only need to remove one halfshaft to do the job. I didn't disconnect the brake line either - there was enough free play to move it without disconnecting. I used some arrangement of bolts and nuts to push the halfshaft out - can't remember exactly how that went now.

It's not terribly difficult, but access is not so easy because the fuel tank gets in the way. I had a photographic instruction sheet that was published by the now extinct M&G International company.

You mustn't push the pinion pin too far back or you will lock up the diff and not be able to recover. You push the pin back just enough so that the other end is protruding, then rotate the diff round so the end now faces you and pull the pin out with a grip wrench. Once the pinion pin is out (mine came out easily) you have to sort of roll the small gear wheels out and roll them back - a bit fiddly, but obvious when you are actually doing the job. As Wade says, the fibre washers will probably have disappeared and the copper ones will be wafer thin.

It sounds more daunting than it really is. Good luck.

Mike
Mike Howlett

This thread was discussed between 08/04/2003 and 09/04/2003

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