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Shimming a diff.... why is this so important?


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#1 Prawn

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Posted 26 June 2005 - 02:27 PM

hey guys, i was ust reading jammy post about locking up the box and removing bits, ive jsut done this last week when changing the final drive in my new jack knight box....

its now time to put the diff back in. i was going to just put the shims in that came out.... but im not sure now :S

ive read a few people say that shimming the diff is VERY important :S why is it so important? and how accurate does it need to be?

what exactly does shimming the diff do? and what happens if its done wrongly?

if it was shimmed correctly before i pulled it apart, will it still be corect going back with the same end covers (alloy plates that the output shafts come out of) and new gaskets?

or should i check it anyway?
ive got the pages in my haynes manual about shimming the diff and stripping the box....

any advice would be great, as i dont fancy taking the engine out again just to shim the diff!!!!

cheers
nick

#2 Guess-Works.com

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Posted 26 June 2005 - 10:31 PM

Basically diff bearings are thrust bearings which rely on a side load to keep the race and the balls together, and this is applied by the shims...miss them out and they will wear and fail.. but, in theory, if you are using competition bearings in the diff, which are steel bound deep groove bearings, which do not rely on the thrust to hold them together, it may not be as bad, however, I always shim the diff as per the book, as it stops everything moving around !!

#3 dklawson

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Posted 27 June 2005 - 01:40 AM

I have gone so far as to make shims because they aren't readily available over here. They are necessary for the reasons GuessWorks said. However, you'll probably be OK without going through re-shimming IF you go through the assembly process like you WERE putting shims in and IF the new gaskets compress to the same thickness as the old ones you're replacing. The shimming assembly process involves several steps to insure that the diff is positioned correctly as well as determining the shim thickness... that's why you need to assemble it like you were reshimming... even if you aren't. Again, if the new and old gaskets are the same thickness and you're re-using the other components, the old shims removed should be OK. (For what its worth... the OLD gaskets, as used on my Mk1, were MUCH thinner than the new replacement gaskets on the market).

#4 Iain Tyrrell

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Posted 28 June 2005 - 12:10 AM

With a road going helical cut diff there is a side load created when accelerating and decelerating. if you dont shim your diff properly it will cause problems for you.




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