Clunk from diff

[RaceDiagnostics]

I've had a long-standing clunk from the diff on my 450sl when going on and off of power. It probably needs rebuilt but I've got zero experience of diffs and the clutches for it's LSD are NLA.

Anyway there seems to be a lot of movement between the propshaft and the diff.

Any thoughts on this?

About half of the movement takes place before any movement in the drive shafts.

 

[bricol]

I'd say that was play in the crownwheel and pinion, not necessarily the "diff". Either worn, or needs backlash adjusting, assuming the pinion isn't moveable in/out, up/down?

 

[Barking Mat]

Isn't there a backplate you can remove to see what's going on in the rear diff ?

 

[RaceDiagnostics]

Isn't there a backplate you can remove to see what's going on in the rear diff ?

That's the next step, however it's not straightforward as the rear subframe will need to be lowered to get access.

 

[RaceDiagnostics]

I'd say that was play in the crownwheel and pinion, not necessarily the "diff". Either worn, or needs backlash adjusting, assuming the pinion isn't moveable in/out, up/down?

In out depth for the pinion is set by unobtainium shims and a crush sleeve, if you go to far then you start again with a new sleeve.

 

[Blobber]

Is there in out movement in the pinion? Tends to be those bearings wear as they do most of the work

 

[RaceDiagnostics]

Is there in out movement in the pinion? Tends to be those bearings wear as they do most of the work

I'd need to do a bit of stripping to find out.

For reference, it's done 172,000 miles.

Just gathering knowledge just now for a job to be done over winter.

 

[Blobber]

If you have a dial gauge and mag base it would be easy enough to see if you have any play in the pinion bearings without stripping the diff?

 

[bricol]

In out depth for the pinion is set by unobtainium shims and a crush sleeve, if you go to far then you start again with a new sleeve.

That should be a specific dimension as set by manufacturer - shims set the distance due to production tolerance stack-up, the crush sleeve simply puts pre-load on the bearings - can be done by measurement and machining a suitable spacer. Torque required to crush the sleeve usually way more than would be necessary to simply tighten the nut - I have cheated with the crush sleeve inside "non-serviceable" transfer box from ZF (their words, not mine) - it has lost preload when it crept up the shoulder it located against - some thin shims later and some careful tightening to a sensible rolling torque on the bearings, all was back to normal (with new bearings).

Backlash set by moving the crownwheel sideways relative to the pinion - either by changing shims behind the crownwheel on the diff carrier, or in the case of the diffs I know, adjusting the whole thing sideways with the bearing cups either side of the carrier . . . and you need to keep the correct pre-load on them too. Been a while, but I recall a measurable amount of spread on the diff casing when winding the cup nuts in.

No such thing as unobtainium shims - if you know relevant diameters and thicknesses you want, plenty of places can do them. Use peelable shims stacks in machine bearing assemblies we design, so easy to get correct pre-load.

 

[dobbslc]

Maybe one for @JOEPRO ?

 

[JOEPRO]

The only thing I haven't rebuilt on a merc yet is a differential I have removed / replaced them plenty of times but never rebuilt one. I have new LSD internals for my w124 500E to fit sometime soon though.

Has the OP checked with his MB or MB classic centre regarding availability of the shims etc? They may still have at least some of them available or worth placing an order if your not in a hurry as sometimes a few orders will get them back into production but your dealer would need to confirm if that is an option or not.

 

[RaceDiagnostics]

Backlash set by moving the crownwheel sideways relative to the pinion - either by changing shims behind the crownwheel on the diff carrier, or in the case of the diffs I know, adjusting the whole thing sideways with the bearing cups either side of the carrier . . . and you need to keep the correct pre-load on them too. Been a while, but I recall a measurable amount of spread on the diff casing when winding the cup nuts in.

No such thing as unobtainium shims - if you know relevant diameters and thicknesses you want, plenty of places can do them. Use peelable shims stacks in machine bearing assemblies we design, so easy to get correct pre-load.

Merc seem to have made this job as difficult as possible.

 

[bricol]

This place:

Metal Shims | Metal Shim Washers | Dobson Gaskets

We have extensive experience in the manufacture and supply of a wide range of metal shims and washers from our base in West Yorkshire.

dobsongasket.com

comes recommended by me - use them a lot for work stuff. If you have a CAD file, or can create one, simple job to email for a price. A pencil sketch will do, and I think a physical sample so they can create the CAD from it.

And for gaskets too obviously

 

[RaceDiagnostics]

I did manage to find this but this whole job looks like a major pita.

I've now started looking for a second hand one but there are very few 450SL left in the UK and even less being broken for spares.