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MG MGB Technical - Noises from back axle

Last winter I fitted a diff.anti clunk kit to my 71 roadster, it got rid of most of the clunk but not completely. Maybe there was more movement than the kit could remove or could something else have been contributing to the noise. Prop shaft for example. Would it be advisable to double up on parts of the clunk kit to remove any excessive play. Maybe I am expecting to much to eliminate all of the noise when lifting the clutch pedal. Thanks for your thoughts.
Trevor Harvey

While wear in the thrust washers accounts for most clunks, wear can also occur in a number of other places: differential cage, the gears, the cross-shaft, halfshaft splines, prop spline. All need checking out as sources.
Paul Walbran

Plus, hub splines if one's got wire wheels.

They can be clunky old axles at the best of times. I once switched one to get less clunk, which wasn't a five minute job. However, as a consolation, even clunky the Salsbury axle is pretty robust.
Peter Allen

And indeed hub splines to half-shaft.

As long as the prop-shaft UJs are OK and the bolts tight I wouldn't worry about it, although I have heard that one of the axle shims is available in two thicknesses.
paulh4

How much free play should there be on the prop shaft, I assume fitting the anti clunk kit does reduce this, so after fitting this less free play should be seen. I’ll have to check out the possibility of finding different shim thicknesses. Thanks Trev.
Trevor Harvey

Ideally none, but you are unlikely to get it to nothing. Measure round the edge of the diff flange how much movement you have - rear wheels locked, and come back.
paulh4

Trevor-
Grip the pinion flange of the differential that connects to the rear U-joint/Universal Joint of the driveshaft/propeller shaft, and then rotate it in order to eliminate any free-play, and then scribe a marking onto its edge and a corresponding marking onto the axle housing. Next, rotate the pinion flange as far as possible in the opposite direction, and then scribe another corresponding marking onto the axle housing. If the marks are 4.5mm apart, thereby indicating 6 degrees of rotation, then yours is a like-new differential. If the marks are 8mm apart, thereby indicating 10 degrees of rotation, then yours is a usable differential. If the marks are 10mm apart, thereby indicating 13 degrees of rotation, then yours is a worn differential. Note that this method of measurement can be misleading because holding the tire and rotating the pinion will involve several combined free-plays: wire wheel hub free-play, halfshaft/quartershaft spline wear / free-play, and pinion gear / crownwheel free-play. Consequently, measuring the free-play of a differential on the workbench using a dial indicator gauge is the most accurate technique. The Original Equipment specification is engraved onto the back of the crownwheel gear. Each matched set will have a matching set number, and the crownwheel free-play for that set, and the amount of shim offset to either the right or the left, all engraved on the back of the crownwheel gear.
Stephen Strange

Being a lazy fella I avoid crawling under the car if I can, so have devised an alternative - measure the backlash at the periphery of the wheel.
Put in top gear, block wheels etc, release handbrake.
Jack up one rea wheel, leave the other on the ground.
Measure backlash at the periphery of the wheel off the ground.
Scale:
As new. About 12-15mm.
Minor wear up to 20-25 mm.
Moderate thrust wear 25-40mm.
Thrusts gone - 50-ish mm
More than that expect significant wear in the cage and/or gears.
Paul Walbran

That includes all play including in the prop-shaft, OD and gearbox.
paulh4

Yes, that is correct, hence there being sime play when everything is as new. We have found it to be a quick, simple and reliable indicator of drive train condition.
Paul Walbran

This thread was discussed between 29/06/2021 and 03/07/2021

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