MB Specs for differential bearings

[Tom Colitt]

Hi

Apparently, there are very few people that rebuild the differentials on these cars and I cannot find any source for specs. to rebuild the differential part only, of the rear axle.

I'm looking for such things as the friction in inch*pounds (or cmkp) of a properly adjusted and torqued pinion drive gear as well as the center cluster once the tapered roller bearings are adjusted with the adjusting ring and shims. Maybe some measurements that would help in selecting the correct shim thickness too (not all shims seem to be available from MB).

Also, can the left hand bearing race (not the wheel bearing) only be removed/ installed using heat. I don't see any place where a bearing puller can be installed behind the race?...

Thanks, Tom

Tom Colitt

[jeffc280sl]

Tom,

Sorry to say I don't have the info you need.  Maybe some pics will help describe what you need.

Download Attachment: diff case bearing surface.jpg
79.5 KB

Jeff C.
1970 280SL 4-speed

[jeffc280sl]

Download Attachment: axle parts lista.jpg
40.48 KB

Jeff C.
1970 280SL 4-speed

[mbzse]

quote:Originally posted by Tom Colitt

.../... the friction in (cmkp) of a properly adjusted and torqued pinion drive gear .../...
.../can the left hand bearing race (not the wheel bearing) only be removed/ installed using heat. I don't see any place where a bearing puller can be installed behind the race?.../..

The rolling torque should be about 30 cmkp, not below 26 for an assembled axle w/o brake calipers or parking brake shoes.

One way to remove the bearing race in the diff housing is to make a round 78mm dia metal plate, then cut off two "flanks" to make like a strip, insert this behind the lip of the race and knock on the strip to push out the bearing race. Keep track of any shims that appear, in order to re-install them
.

/Hans in Sweden

[Tom Colitt]

Thanks for the pictures although I already had taken everything apart, except for the one bearing race. Hans' solution for removing it sounds like a good solution. I was going to try that too, but I wasn't quite sure whether the shoulder I see behind the bearing race was a shim that I could pull out or not, but it must be....I'm surprised that no MB manual covers this.

As far as the torque you mentioned, Hans. Where does that number come from and is this number measured for the friction of the pinion gear alone (which is what I would like, so I can set up each bearing clearance separately), or is it measured, already engaged with the spider gear and possibly the axle shafts and wheel bearing friction (torque) too? Is there any other information on what measurements I will need to set the new pinion up correctly? Should I buy different thickness shims from MB so that I have them ready upon re-assembly, or are all the pinion and spider gear sets machined to such tight tolerances that it is actually the differntial housing's bearing seats that have the variable dimensions (meaning that I can use the same old shim thicknesses even if I change the bearings and gear set? What's your opinion? Hans? Joe? Others?

Tom Colitt

[mbzse]

quote:Originally posted by Tom Colitt

.../...I'm surprised that no MB manual covers this

Of course M-B have factory literature that cover all aspects of workshop tasks for their vehicles. However, these are aligned towards professionals, and not tuned to hobbyists needs. The M-B workshop manuals are all like a long "series" you could say, and procedures are not really repeated from binder to binder. The re-build details for working with the differential are probably in the w/s manual for the Ponton or the like (I may check this at a later time). A further point to consider is, these manuals often refer to specialized M-B factory tools and jigs to be used that one doesn't have access to anyway...

quote: As far as the torque you mentioned, Hans. Where does that number come from?.../… Is there any other information on what measurements I will need to set the new pinion up correctly?

A diff rebuild is a pretty advanced workshop exercise. I suggest you obtain the M-B Book of Tables for yourself, the one from 1969. All the little numbers and specs you require are printed there.
Torque for pinion alone is given as 16-18cmkp, well oiled new bearings. For the complete rear axle with brake calipers removed it is given as 26-30cmkp


/Hans in Sweden

[George Des]

Tom,

I'm in the process of doing this same thing to a rear axle I picked up from Walter Klatt recently. What did you eventually do on yours as faras shims and torque settings.

George Des

[Tom Colitt]

Hi George

Replacing the center cluster and bearings and setting it up correctly is quite a time consuming job, even if you have experience, as it can take several rounds of removing and installing the bearings and shims. It is a quite a job and can take quite some time if you've never spent time with this. I did receive a set of specs from one of our list members that helped me do this job myself this time, but in the future I would outsource this to a shop that can do it much more quickly and efficiently. If you take just the center cluster to any good rear axle shop, they can set up the clearances and friction of the center cluster for you, even if they say they don't do Mercedes. The US cars basically use the same principle. They will be better equipped to fabricate different shim thicknesses which may be needed if you are changing the gear set, possibly even if you are just replacing the tapered roller bearings too.

Good Luck, Tom

[George Des]

Tom,

Couple of questions (1) did you use the same (original) ring and pinion set-up in your rebuild? (2) if so, was there any change in the thickness of the left axle shim or the pinion shaft shim required? I'm thinking that these are the only two ways to make any adjustments to the pinion depth and backlash and if only the bearings are changed out for newer ones, then the only way things that could possibly change in the set-up would be caused by the tolerances within the newer bearings themselves or perhaps by a burr or soemthing else that would prevent the bearing cups from fully seating in their bores. I would have to guess that those tolerances on the bearings (Timken and SKF) should be tight enough that it shouldn't make a difference. Am I wrong? I also noticed that SLS only sells one thickness of the pinion shim and three or four left axle shims all separated by about .1MM. Also, the preload on the carrier bearings--is this set with that staked slotted ring on the right side. If so, what is the torque setting for that. Appreciate your help.

George Des

[Tom Colitt]

Hi George

I did change the gear set and so I needed to experiment with different shim thicknesses until I had the correct adjustment. The only other way to do this is if you have an elaborate measuring set-up. I agree the shim thickness will probably not change if you use the same gear set. Just use machinists Blue (Prussian Blue) to verify the load pattern on the teeth. The first pre-load is set for the pinion gear alone. It is best to check the existing preload before you take everything apart. You should use an in-lbs torque wrench with a range of 0 to about 30 in-lbs. Or you could wrap a cord around the axle shaft and pull it with a scale and multiply by the radius of the axle shaft...

Use a new crush sleeve. Then you set up the correct clearance (back lash) and pre-load the completed assembly by adjusting the slotted nut you mentioned. I made a tool to fit that nut, but you should be able to adjust it with a punch?.. The problem is (as far as I remember) that the values I had, give you a torque for the complete assembly, including the friction from the wheel bearings and so you have to disassemble the cover every time you want to make an adjustment. This is why I said it is easier to pay a shop $150 to set that part up for you. If you give me your email address I can email you the pages. Also new bearings and seals are allowed higher friction values although, I am a bit skeptical for the large allowances made for this in the MB data and so I feel you will be safer having an experienced shop do this final step.

Best, Tom

[George Des]

Tom--thanks for this info. Things are becoming much clearer now on how to do this. I do have a new crush sleeve and believe it or not one of the proper pin sockets for the pinion nut--bought this several years ago after several attempts at fabricating one--never quite worked well. Also have one of those click in-lb torque wrenches somewere downstairs so I won't have to do the spring scale trick--never did trust that method. I will make one up for the slotted ring so I can torque that properly--will let you know how it goes.

George Des

[Tom Colitt]

George

You slightly misunderstood me. I meant that you can't really adjust the slotted nut for the center cluster while the whole thing is assembled as my torque specs require, no matter what kind of tool you have.

You certainly always would want to use the correct pin tool to achieve the high torque required to crush that pinion bearing crush sleeve. The other torques I am talking about are very light torques to overcome the bearing friction which is a measure of the correct bearing pre-load.

Tom