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MG MGB Technical - CLUNK !!!!

My CD player broke and is out being repaired and now my car has developed a clunk in the rear,noticeable at gear change when revs are a little to low on clutch engagement (should read now I have no loud music I can hear my clunk).
I suspect one or more of the following.
Worn wheel splines.
Diff. backlash.
Drive shaft spline wear.
Worn universal joints.
Can anyone advise on method to identify the main cause. Or should I just replace the universal joints as the easiest and cheapest option ?
I suspect when my CD player is back my problem will disappear.
David Levy

David,It is easy to check for wheel spline wear by jacking up the car with the handbrake applied and try to rotate the wheel back and forth.
You should also be able to feel for wear in the uni's by gripping the tail shaft and similarly twisting back and forth!
You might like to look at this page for the likely cause
Eric Martin

Do the splines on the drive shaft wear out at all? I don't remember hearing about that in the rear end clunking posts. I imagine the U-joints would wear out first.

The other thing to check is that everything around the rear suspension/axle is bolted up nice and tight. I once had a clunk that turned out to be a rear shock not bolted up snugly.

Simon Jansen

The drive shaft splines can wear as a result of road grit and other rubbish getting in there but as you suggested the U Joints are normally the first to show signs.

Cheers , Pete.
Peter Thomas

The splines will always wear as there has to be free play between them so you can get the wheel on and off without a press! The wheels will always move back and fore under acceleration and braking, even when the spinners are tight. From new the clearance is so small that you can't hear the movement, but it does have a slight impact on the faces of the splines, which gradually get cold forged into a narrower tip, which increases the clearance. Eventually you can hear the clunk or click, and wear gets even more rapid. The tips can get so narrow that they eventually shear, not what you want on the fronts, although they tend to stay in the same place as apart from braking in reverse the forces are all one way, unlike the rears.
Paul Hunt

David, you didn't say what year your car was. If it one with the rear sway bar it makes the diff more rigid. It took me a long time to find it the first time when he had an annoying 'ping' through the drive shaft. It was the diff flange moving on the spline by the few thou clearance it had. I cured it by removing the flange - after marking shaft, nut & pinion so it could retightened to the same plce after putting a couple of drops of 'loctite' on the spline.
Garth Bagnall

I also had front and rear suspension clunks. The clunks disappeared after I re-tightened all fasters for the rear leaf springs and all of the dampers. I was surprised by how lose they had become.
T. A. Vander Biezen

The thrust washers in the differential are notorious for wear and give a distinctive clunk with load reversals. Fortunately they are cheap to purchase and not difficult to replace. I even had one axle where the washers had completly disappeared. Jim
jim soutar

My clonk was evident when changing direction.. forward/reverse
An anti clonk kit on the rear diff solved the problem !
AT McGlasson


Think the direction you are heading is what I would do. Put it up on jack stands and pull the drive shaft. See if you can beat John Twists time at changing the u-joints. His You Tube video on this process makes it easy.

U-joints are inexpensive and might as well change these anyway.

While you have it up, try Eric's suggestion on the wheels. If that is not conclusive, pull the wheels and look at the splines. British wire wheel has a good diagram of worn splines. Look at both hub and wheel splines.

Once it is all back together, you have either found the problem or eliminated two potential causes.

David & all the R/R wire wheel hub/spline is the first one to wear, if the veh has wire wheels. As also metioned the rear axle assy may need attention, not expensive, if you do it your self.
Len Fanelli

try all of the above then

a minor clunk is no big deal.

This thread was discussed between 19/04/2009 and 23/05/2009

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