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Trouble with LSD Diff and Cover
https://www.ausmini.com/forums/viewtopic.php?f=2&t=89274		 Page 1 of 2
Author:  MiniBob [ Mon Apr 27, 2015 12:01 am ]
Post subject:  Trouble with LSD Diff and Cover
Need some help here please.
Existing gap is .008 plus
Compressed gasket .013 equals
........................ .021 less
Reqd gap (pre load) .002 means that
Required shim is .019

Am I doing my sums correctly??
The Mini Forum feature also states 4 thou pre load.

The gearbox rebuild link on here states that;
"On standard diffs the shims for this purpose are fitted on the crownwheel side,
but go on the other side when a limited slip diff is being used"

Has anyone done this?
Thanks.
Author:  drmini in aust [ Mon Apr 27, 2015 8:35 am ]
Post subject:  Re: Trouble calculating LSD shim required.
Gaskets are so thick now I put a .010" shim on the RH side to start with, then shim the LH side. Old paper gaskets were only around .005" I think.
This is with stock diffs, not LSD. Why would they be different?
Author:  Beanie [ Mon Apr 27, 2015 8:40 am ]
Post subject:  Re: Trouble calculating LSD shim required.
what lsd do you have ... if its an ATB then shim as per normal

if its a Tranx or a plate type diff you need to shim from the opposite side to help with clearance issues

and i shim to .004"

Beanie
Author:  MiniBob [ Mon Apr 27, 2015 1:43 pm ]
Post subject:  Re: Trouble calculating LSD shim required.
drmini in aust wrote:
Gaskets are so thick now I put a .010" shim on the RH side to start with, then shim the LH side. Old paper gaskets were only around .005" I think.
This is with stock diffs, not LSD. Why would they be different?


Thanks Doc. I was referring to this "How To" link;
viewtopic.php?f=25&t=85150
I am fitting a Quaife LSD with new bearings too. The feature (page 65 middle column just under the photo) doesn't refer to any particular type or make.
Nothing in the Calver book either.
The diff body can only go so far to the right before the bearing touches the housing. At that point tho, the crown wheel isn't seated properly.

My understanding is that diff must not be allowed to move too much.
Think your approach is good, shim at both ends.
Author:  MiniBob [ Mon Apr 27, 2015 1:49 pm ]
Post subject:  Re: Trouble calculating LSD shim required.
Beanie wrote:
what lsd do you have ... if its an ATB then shim as per normal

if its a Tranx or a plate type diff you need to shim from the opposite side to help with clearance issues

and i shim to .004"

Beanie


Thanks Beanie. It's a Quaife. I think I'll give Swiftune a shout again, just to make sure.
Author:  simon k [ Mon Apr 27, 2015 1:59 pm ]
Post subject:  Re: Trouble calculating LSD shim required.
shim as normal, but I had to put a shim between the bearing inner and the diff itself because otherwise I had about 10 shims under the side cover... they were a bit hard to wrangle
Author:  drmini in aust [ Mon Apr 27, 2015 2:17 pm ]
Post subject:  Re: Trouble calculating LSD shim required.
simon k wrote:
shim as normal, but I had to put a shim between the bearing inner and the diff itself because otherwise I had about 10 shims under the side cover... they were a bit hard to wrangle

Put the gearbox on its RH side. Then the multiple shims are no problem to keep in place.
Easiest to do with the whole thing on the engine stand, but if not, it's pretty easy to block it up off the floor.
Author:  mini_mad_matt [ Mon Apr 27, 2015 6:41 pm ]
Post subject:  Re: Trouble calculating LSD shim required.
MiniBob wrote:
Need some help here please.
Existing gap is .008 plus
Compressed gasket .013 equals
........................ .021 less
Reqd gap (pre load) .002 means that
Required shim is .019

Am I doing my sums correctly??
The Mini Forum feature also states 4 thou pre load.

The gearbox rebuild link on here states that;
"On standard diffs the shims for this purpose are fitted on the crownwheel side,
but go on the other side when a limited slip diff is being used"

Has anyone done this?
Thanks.



Your "existing gap" is measured with a feeler gauge between the side cover and the diff housing yea?

If so, then when you add the gasket you have only moved the sidecover out a further 5 thou (had a 8thou gap and now no gap but 13thou gasket). So you now have 5 thou clearance on the bearing.

So you need to shim 5thou plus the preload. If your bearings have thrust written on them they take more preload then normal ones. Consult a workshop manual for preload amounts.


When i put the diff in, i sit it towards the drivers side and then put that sidecover on with gasket and no shims, so that as i bolt it up it pushes the diff over to the passenger side and there is no clearance on the drivers side. Then just do the no gasket measurement etc on the passenger side and put it all together. Give it a spin and if nothing hits your good to go.
Author:  MiniBob [ Mon Apr 27, 2015 9:26 pm ]
Post subject:  Re: Trouble calculating LSD shim required.
mini_mad_matt wrote:
MiniBob wrote:
Need some help here please.
Existing gap is .008 plus
Compressed gasket .013 equals
........................ .021 less
Reqd gap (pre load) .002 means that
Required shim is .019

Am I doing my sums correctly??
The Mini Forum feature also states 4 thou pre load.

The gearbox rebuild link on here states that;
"On standard diffs the shims for this purpose are fitted on the crownwheel side,
but go on the other side when a limited slip diff is being used"

Has anyone done this?
Thanks.



Your "existing gap" is measured with a feeler gauge between the side cover and the diff housing yea?

If so, then when you add the gasket you have only moved the sidecover out a further 5 thou (had a 8thou gap and now no gap but 13thou gasket). So yxyou now have 5 thou clearance on the bearing.

So you need to shim 5thou plus the preload. If your bearings have thrust written on them they take more preload then normal ones. Consult a workshop manual for preload amounts.


When i put the diff in, i sit it towards the drivers side and then put that sidecover on with gasket and no shims, so that as i bolt it up it pushes the diff over to the passenger side and there is no clearance on the drivers side. Then just do the no gasket measurement etc on the passenger side and put it all together. Give it a spin and if nothing hits your good to go.


Thanks Matt, of course you are spot on. Gasket doesn't add to the gap but fills it :roll:
I rang Swiftune and they confirmed ok to shim at both ends.
I fitted the type of bearing that doesn't have thrust stamped on the face.

Thanks for clarifying that, now off to check the manual and re- do my sums.
Your fitting method is the same as detailed in the articles I have seen
Author:  MiniBob [ Tue May 05, 2015 3:06 pm ]
Post subject:  Re: Trouble calculating LSD shim required.
So I got the shim situ sorted, thanks all.
Fitted it all up last night, including torqueing the bolts.
The whole diff was completely locked up :evil:
It wasn't fitted with a gasket when I stripped it down, so I didn't fit one on re-assembly. I have fitted new bearings tho, so am guessing I now need the gasket.
PITA because I didn't do a dry run, soddin' gasket goo everywhere :roll:
Really surprised that it didn't loosen up until I undid the four main bolts (35ft/lb) Wouldn't have thought that the gasket would make that much difference.
Any suggestions as to other possible causes??

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Author:  timmy201 [ Tue May 05, 2015 4:31 pm ]
Post subject:  Re: Trouble with LSD Diff and Cover
I found that there was two different ways to measure the shims. The first way is like you have done, with the gasket and side cover done up on the right and the gap measured on the left
http://www.theminiforum.co.uk/forums/to ... /?p=105274
And the second way was in this video. On this one he leaves off the diff housing and puts on the side covers with the gaskets. This was a little easier for me to get my head around, and you can make sure the diff spins ok.
http://www.youtube.com/watch?v=HgW_r5ZjSm8

I measured mine both ways and got the same number. I must have measured it 10 times to make sure I got it right..

Did the new bearings go on the right way? My new bearings also specified the pre-load on the box.

Mine needed something like 20 thou of shims, so instead of chucking a 020 on the left, I put a 010 on each side. If the diff goes too far to one side it can rub on the diff housing.

So did you not use any side cover gaskets? That would have thrown out your shim calcs, and might have put too much pre-load on the bearings?
Author:  MiniBob [ Tue May 05, 2015 4:59 pm ]
Post subject:  Re: Trouble with LSD Diff and Cover
Thanks for the details.
That is the same video that I used. And I measured up in the same way.
After speaking to Swiftune they advised fitting a 20 thou to each end.
The diff only locked up after I had torqued up the top 4 bolts @ 35ft/lb.
Pretty sure it's not being caused by the end plates @ 18ft/lb.
But I will have a try with some thinner shims, bought two in each of the three sizes.
I'll check the boxes that the bearings came in too.
Author:  mini_mad_matt [ Tue May 05, 2015 5:35 pm ]
Post subject:  Re: Trouble with LSD Diff and Cover
The diff housing isn't hard up against the lsd is it?
Author:  drmini in aust [ Tue May 05, 2015 7:42 pm ]
Post subject:  Re: Trouble with LSD Diff and Cover
I'd say it's locking up because you have no diff housing gaskets.
Undo the top bolts and put a feeler gauge in there. Any more than a .002" gap, I'd be using gaskets.
Author:  MiniBob [ Wed May 06, 2015 4:11 pm ]
Post subject:  Re: Trouble with LSD Diff and Cover
mini_mad_matt wrote:
The diff housing isn't hard up against the lsd is it?


I'll check again but I don't think so.
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