Diff pinion bearing friction torque - Mercedes-Benz Forum
 
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post #1 of 10 (permalink) Old 08-17-2018, 11:43 AM Thread Starter
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Diff pinion bearing friction torque

I don't have the correct tool to measure this ahead of changing the oil seal, this is my version.



I then loaded up the bag till the pinion started to turn.



The total weight of the bag plus bolt was 65g at 10 cm is 650gcm or ~ 6.4Ncm.

What I donít understand is that the manual, section 35-550 says that a used diff should read between 50-100Ncm.

I donít understand how I can be on order of magnitude out.

Can anyone point out a stupid mistake I have made?



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post #2 of 10 (permalink) Old 08-18-2018, 02:05 AM
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I dont know much about this final drive .But if like others you can ruin it if to much torque is put on the pinion .It must be set right or damage can be caused ,.

This is a retro ride .
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post #3 of 10 (permalink) Old 08-19-2018, 02:15 AM Thread Starter
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Surely someone must have rebuilt their diff?


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post #4 of 10 (permalink) Old 08-19-2018, 05:28 AM
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Originally Posted by RaceDiagnostics View Post
Surely someone must have rebuilt their diff?
Please see this link. Looks like @nobby saved a copy.
https://www.benzworld.org/forums/r-c...f-rebuild.html
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post #5 of 10 (permalink) Old 08-19-2018, 06:59 AM
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I'm not sure if your calculation is correct. The radius of your lever arm extends past the pinion to the edge of the flange that holds the flex disc. So your lever arm is a bit longer than the 10cm you are using in the calculation. What you are measuring is the break away torque that in theory should be slightly higher than the continuous frictional torque. I don't think you'll be able to get an accurate measurement with the method you are using and I recommend you get one of those needle indicator torque wrenches.

I have never rebuilt a rear diff but I'm not surprised with your low readings on a diff with old used bearings. Are you replacing the pinion bearings? If your throwing all new parts at it why not just torque it until you have the correct setting and not worry about the old frictional torque setting?
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post #6 of 10 (permalink) Old 08-19-2018, 07:31 AM
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I think youíre off because 1 gcm is not the same as 1ncm. You can google conversion charts for these two units.


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post #7 of 10 (permalink) Old 08-19-2018, 07:37 AM Thread Starter
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Originally Posted by RLT61 View Post
Please see this link. Looks like @nobby saved a copy.
https://www.benzworld.org/forums/r-c...f-rebuild.html
Great, thanks for that, I've PMed Nobby for the write up.


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post #8 of 10 (permalink) Old 08-19-2018, 07:44 AM Thread Starter
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If your throwing all new parts at it why not just torque it until you have the correct setting and not worry about the old frictional torque setting?
My plan was just to change the oil seals as they were leaking till I found this low reading. There is also a bit of backlash between the pinion and crown wheel. I spoke to an indie (trusted and respected MB specialist) about it and he advised looking for a lower mileage second hand unit as new internals are extremely expensive. So for the time being I will put on the new seals and refit with the pinion nut nipped up to the spec value for used bearings.


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post #9 of 10 (permalink) Old 08-19-2018, 08:58 AM Thread Starter
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Originally Posted by masand68 View Post
I think youíre off because 1 gcm is not the same as 1ncm. You can google conversion charts for these two units.
Where did I use 1gcm = 1ncm ?


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post #10 of 10 (permalink) Old 08-19-2018, 10:09 AM
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Originally Posted by RaceDiagnostics View Post
Where did I use 1gcm = 1ncm ?


Sorry, My mistake. I skimmed your conversion too quickly. I ran your numbers and came up with the same thing you did. Your measurement times 10 would put you in range but I canít see where we missed a decimal place.



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