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MG Midget and Sprite Technical - axle clonking ??

hi all
Friend of mine, seebring a series midget, has recently fitted an overhauled diff and with a new 3.7 cwp.
Since the fitting there is an all new noise on overrun. All the time foot on throttle, no noise. Foot off throttle clonk, clonk clonk consistent with road speed. Bit like a shot uj. As speed reduces, noise increases . Just before the car stops is its worst.
UJ seems ok but all was fine before new diff.
All ideas appreciated.
rgds tony
tony boyle

It sounds like an issue with the overhauled diff.
Dave O'Neill 2

Wheel nuts or splines not seated? Or a wheel cylinder catching on the half shaft mushroom?

Just thinking about things that may have been disturbed when swapping the new diff in.

Are the bolts from the prop to diff tight?
Dominic Clancy

I agree with all the above suggestions & here are a few more: excessive backlash, loose pinion nut, worn / damaged spider gears. I'd be pulling out the center section and checking EVERYTHING before it gets extremely expensive. This does not sound good!
Stan Kowznofski

Could installing the prop shaft with the u-joints out of phase cause this kind of noise?

C R Huff


It shouldn't do as it can only go on 2 ways and should be balanced as a separate unit when built anyway.

I would be looking to pull the final drive and give it and the rest of the axle a close inspection to see if the supplier missed something important or some silly assembly issue, it wouldn't be the first time something had been missed. Who did the rebuild?
David Billington

Sounds like a problem with sun(side)/planetry gears to me
William Revit


What do you think would cause that as I've used diffs with completely missing sun gear thrust washers and worn planet washers which were quite and didn't rumble or clonk. Hopefully any competent rebuilder would pick up damage to the diff gears and replace as appropriate.
David Billington

If there is excessive clearance between the side and sun gears there will be a clonk as you get on and off the throttle as the slack is taken up just like a badly worn uni.joint does
I've had B/W diffs with the side gears worn that far into the housing that they will go clonk clonk clonk just rolling along at 40-50Kph as the side gear/axle climbs up and drops in the crownwheel carrier as it rolls along -
As you say-- "Hopefully any competent rebuilder would pick up damage to the diff gears and replace as appropriate."

But-the fact remains-the new diff clunks where the old one didn't

Maybee, With the gearbox in4th gear, Chock one back wheel,jack the other back wheel off the ground and rotate it back and forward and see if there is an obvious clunk from somewhere that can be identified--

Tony, was it a complete axle assy or a centre
William Revit

Tony- with the wheel off the ground hold it at 6-12 o'clock and push pull against each other top in bottom out then topout bottom in and see if you can detect if the inside end of the driveshaft is moving up/down causing a clunk
William Revit

Not disagreeing that it may be down to an internal fault with the new diff, but I would most certainly be thoroughly checking inside the rear drums, prop shaft and rear wheel mountings first. Admittedly diffs are easy to remove but it would be a bit annoying draining fresh oil and removing half shafts if you later found it was something simple and the diff itself was perfect!

hi all
many thanks your input
the diff only was changed. i/2 shafts out diff out/i
nothing else removed. The diff has been back once, out of the car to the rebuilder an i believe it then had new side geasr.
As you said william, the new axle clunks, the old one didnt
we will do some of the off the ground checks suggested
thanks again

tony boyle

This thread was discussed between 09/03/2018 and 10/03/2018

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