Grinding Rear Axle

[hobbsfamily]

I have a 1973 V12 Series 3 2+2 Coupe with a rear axle grumble started about 2 years ago and is worse when cold. Had the whole rear axle removed and dismantled to check the gears, drive shafts etc and no problems but a cracked diff shim. This was replaced and the axle reassembled and limited slip diff oil added. It lasted about 50 miles before it started to grind and knock again especially when all the oils were warmed up properly. It is worse when cornering very slowly almost as if it is jumping the cogs. The axle was removed and dismantled again but absolutely everything is in order so was reassembled and new oil added but the problem is still there.
Has anyone any ideas.
Thanks Mike.

[David Oslo]

Noise in corners also points to wheel bearings. Loading them differently due to cornering (sideways) loads as opposed to just straight ahead.

I would also consider changing the universal joints on the driveshafts. Although you write that these have been checked.

Many years ago (on a Triumph) I had a cyclic squeak noise in corners, once every wheel revolution. Could not for the life of me figure out what it was. Then after a few months the rear stub-axle failed and the wheel literally fell off. Luckily I was at a traffic light and semi stationary. The noise I had heard was the growth of a crack that started from the square corner of a woodruff key slot on the axle. Like growth rings on a tree, I could see the waves of crack growth.

[hobbsfamily]

Thanks for that David I'll get the wheel bearings, stub axle and universal joints inspected carefully rather than just looked at to see if they show any damage/wear which might provide some answers.

[christopher storey]

I suggest that you put the back of the car up on axle stands under the lower wishbones, take the wheels off, and then run the car at an indicated simulated speed of say 30 mph . You will very soon hear if wheel bearings are at fault , and with a rubber tube stuck in the ear you should be able to localise the noise easily

[hobbsfamily]

Thanks for the extra advice. Will do it in about 3 weeks when the MOT is due at the same time.

[PeterCrespin]

Bearings usually make most noise when carrying load. Hanging free might not be the best test and you can't simulate the reported cornering issue on axle stands. It won't do any harm though and might highlight something, so worth a punt.

[christopher storey]

Not sure that I agree with you , Peter, where it is tapered roller bearings . Certainly, on the two cases of rear roller failure I have had, the noise was easily detected by the method I have described . These bearings were designed to last the life of the car, but a. the cars are now at least 3 times older than their design life and more to the point b. there is a tendency for the hub carrier dust caps to go missing and all sorts of foreign matter then gets in

[PeterCrespin]

Truer for tapers yes, but in general fully-assembled bearings assemblies still exhibit worst grumbling/rumbling symptoms when subject to their designed loads, rather than freewheeling under no radial load.

The lateral loading is also impossible unless grossly overtightened/under-shimmed. But as I said I'd do as you recommend because I certainly can't assume the result would be negative. Actually, it's probably an ideal test for UJs at full droop on axle stands, because it would be more likely than not to show up due to the extra articulation.

[christopher storey]

Peter, yes, I agree that ideally one should reproduce the exact conditions under which the noise arises. The value of my suggested test, however, is that one is not trying to discern the noise against ( in particular ) tyre noise, and you do not encounter the problem of the noise being "telegraphed" to different parts of the car

[PeterCrespin]

Yes, one would hate one's passenger to do an 'Isadora Duncan' with a bearing stethoscope... :-(

[44DHR]

Sorry for a late response, but as I have a Series 1 I don't come down to these depths in the Forum

However, I do work on these Salisbury 4HA diffs and my question is did the Limited Slip diff get opened up and the plates checked ?

There is a series of clutch plates on each side inside the Powr-Lok assembly and a Belleville spring plate at each the end of the clutch pack which comprises the series of friction and driven plates. These are normally locked together, but open to allow cornering motion and it could be you have crud beween them or badly worn plates, or even a cracked Belleville spring plate making the noise on cornering.

regards,

Dave

[Mountain King]

I was also going to suggest checking the diff would be a good starting point. Is it original, ie LSD? Jack the car rear up and turn the wheels to see if ok, also use a "stethoscope" ie a piece of wood or pipe to listen to the diff gears for noise when rotating.

Andy

[Sjmmarsh]

I had a grinding noise on mine after going round a tight corner - it sounded like a tyre rubbing on a wheel arch,but wasn't. Changing the diff oil made no difference. However after a track day at Blyton the problem has gone - I reckon these cars just need to be used! (My logic was that if it was going to break down, I'd rather find out on a track day than on my trip to Le Mans...)

Steve