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MG MGA - Rear clunking noise

I’m not sure if I am paranoid or weather I have a problem. When I go in reverse and then shift into 1st I get a pretty load clunk that is coming from the rear. The "U" joints have been replaced so I know it's not that. Does anybody get a similar sound? Please tell me it's normal :)


WMR Bill

Wire Wheels loose on splines?
J Bray

I would check the axel splines on both ends, the wheel splines, the drive line u joints and your rear spring bushings. Have a good day!

John

John
John Progess

Not normal.
JB and JP are both correct. First check those splines for wear.
Sandy
Sandy Sanders

One more thing to check - are the U bolt nuts done up tight? Otherwise the axle can rock on the leaves and may cause some noise.

Failing that, it could simply be excessive lash between crown and pinion, which would need to be adjusted out.

Maybe jack it up and grab the driveshaft and move it back and forth and see how much play you have.
Bill Spohn

Also,
Don't forget to check the tightness of the driveshaft universal flange bolts. Even though new "U" joint are installed the bolts can be loose.
Do as Bill Spohn suggests, but also, with one rear wheel touching the ground or held by a helper, roatate the opposite wheel back an forth and observe what you hear/see.

Cheers,
GTF
G T Foster

With wheels on the ground or hand brake locked (or both) and gearbox in neutral, try turning the propshaft (differential input coupling) back and forth. If you get more then 1/8 inch motion at the edge of the dust cover it will clunk in operation. The most common cause is worn thrust washer behind the bevel gears in the differential.
Barney Gaylord

Barney, I do now believe this is the case. It is just about at a 1/8. Now that it is driving season is this something I can put off till next winter? Do I need to be concerned with a catastrophic failure at high speeds? If it does fail will it lock up or just spin? Thanks to all for the great suggestions in helping me narrow this down.
Cheers, Bill
WMR Bill

This is not on the verge of being a catastrophic failure, unless you abuse it a lot (like regular jack rabbit starts with autocrossing). These may commonly clunk for years before being repaired, and seldom break.

The thrust washers, gaskets, seals and EP gear oil are cheap, and it's a few hours to fix. Go ahead and order the parts to do the repair when you have a day to play with it. Meanwhile enjoy the cruising weather.
Barney Gaylord

Barney, how does the 1/8 inch translate to movement at the differential end? I measured my movement between the prop shaft and the diff casting and got about 3/16 inch -4 mm or so. Is this the same measurement position since the measurement recorded depends on the radius from the centre. If I've got this right 1/8 inch seems quite demanding for all the gears within the diff. Even at 3/16 inch I don't much clunking other than when I change between reverse and forward gears and perhaps a little when I'm driving slowly.
J H Cole

There should of course be no freeplay at all in the universal joint itself, so the motion should be the same at the propshaft OD or at the U-joint yoke or at the pinion input dust cover. 1/8 inch total free motion at the circumference should give no problem and probably no noticeable noise. Freeplay of 3/16 inch most likely will make noise and is a good indication that the thrust washers should be replaced (sometime soon at your convenience). 1/4 inch freeplay will definitely make clunking noises just going on and off throttle. For this condition I would make time to fix it immediately before it might get worse or fail something on the road.

Another problem that might cause a clunk and free play at the differential input yoke is a loose nut holding the yoke on the pinion shaft. This allows the shaft and pinion gear to float endways, which in turn might cause gear howling on overrun as well as clunking. This condition could go from bad to catastrophic failure in a very short time, so it is always good to check up on any suspicious noise as soon as you notice.
Barney Gaylord

Barney, I've bitten the bullet and taken the differential out for inspection - now I'm in unknown territory. There is very little movement between the crown wheel and pinion but there is noticeable movement between the differential sun and planet gears that I assume is due to wear in the fibre thrust washers. On your web site you talk about a full rebuild but can I replace the thrust washers without loosing the crown and pinion set up?. I really don't want to get into adjusting the preload and gear meshing unless its essential. Looking at the Chicagoland site there are pictures showing the whole assembly with crown wheel taken out of the differential housing leaving the pinion in position. They say that this does not upset crown wheel and pinion adjustment but surely it must do? I don't think you've ever written up a step by step for this procedure.
J H Cole

J H, -- The replacement procedure pictures and notes I had placed on the CMGC web site is correct. See here: http://chicagolandmgclub.com/photos/a_diff/index2.html
The differential assembly with the ring gear does need to be removed from the carrier for access to the locking pin for the pinion shaft. The shims used to align the ring gear to the input pinion gear are captured inboard of the main ball bearings, which are in turn pressed in place. These shims will not be disturbed, so you can reassemble it without affecting the gear alignment.
Barney Gaylord

This thread was discussed between 17/04/2008 and 28/04/2008

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