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Is it the Diff?

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I have this clunk as I drive maybe worse on overrun but I think it there all the time, new UJs on prop and half shafts so not those...I have some play in the diff and enclose a couple of videos (turn sound up high) do you think this is the cause of my clunking? Any comments welcome

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I dont think thats particularly bad amount of play in the diff and wouldnt explain the clunk when driving. Diffs tend to whine or in the later stages sound rough but not clonk in use. I take it the sound is regularly but does its rate increase and decrease with speed? If it does perhaps you could get the back wheels securely off the ground and run it in gear to locate the source better...

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thats just backlash in the differential gears , they are straight cut bevel gears and must have some backlash 

the backlash is dependant on thrust washer wear but you can end up with lots of work for no improvement 

they dont do any  real  rotation in normal driving only slow rotation on corners and roundabouts etc

this backlash can give you a good  1/8th  turn on the prop coupling as all the clearances play catch up 

clunks on drive/overrrun  are not usually from the diff its nothing to do with crownwheel backlash which needs a very light feely hand to detect 

as if the diff is stripped out you need a good dial indicator and are looking for 0.007/0.012"  backlash on the crown wheel teeth 



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  • 3 months later...


I posted somewhere else - an accident my ex-wife had in my absence in our Herald 1200 saloon following rear end clunking for some considerable time:- I too, had multiply changed all the UJ's (definition of madness doing the same thing over and over). I'm now pretty sure it was one rear half shaft (yoke end) pin-through-pressed spline joint broke somehow. Everything became loose at rear end and she and my daughter were lucky not to have crashed. The clunk had puzzled me for donkey's  - and I still think to this day that I would have had NO WAY of figuring out that the pin was broken/coming loose and would allow the splined shaft to come away from the yoke. I sincerely hope it won't happen to anyone else. Stay safe.

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35 minutes ago, Pimp my Vit said:

Where exactly is this pin, I look at the diff diagram and can't see it?

If I'm correct in what Colin is saying above, it's the pin that holds the splined fork onto the shaft. There were some very poor versions around some years back. Here's a photo, and at the top of the yoke where the UJ fits you can see the hole:


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Indeed, some have been made with just a roll pin, which is totally unsuitable and will very likely break at some point. 

58 minutes ago, Pimp my Vit said:

Where exactly is this pin, I look at the diff diagram and can't see it? Mine is still clunking and I just can't track it down, thinking a rolling road (mot brake test type rolling road) might allow me to track it down.

Are you sure it isn't UJ endfloat? It only takes a tiny bit, but tends to be more of a ticking than clonk. Then again, worn UJs are difficult to diagnose as they are under huge tension from the spring.

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