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Setting Up A Diff


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#1 germini30

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Posted 14 July 2018 - 12:14 PM

Putting my diff back in later. I need to shim it. Bit confused as I have seen I few different ways of doing it. The easiest way I have seen is to put the diff into the gearbox housing then fit both side covers and gaskets using two bolts, can't use them all as at this stage the diff cover will still be off. Then push the diff all the way towards the clutch end and then measure the clearance between bearing face and side cover. Is this the best way to do it????

#2 Spider

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Posted 14 July 2018 - 06:18 PM

I tend to find it faster and more accurate to do it by 'trial and error' with fitting shims or taking them out as needed until the gap is 0.001 or 0.004" depending on the bearings fitted. The sides on the cases that the side plates fit too are rarely 'square' so I've found trying to measure to within +/- 0.002" here a fruitless task.



#3 germini30

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Posted 15 July 2018 - 01:50 PM

Refitting my diff to my 1989 998. The diff is a 3.1. I have put the diff into the gearbox and pushed it towards the flywheel and nipped up the cover bolts. I then fitted the side cover with gasket to the flywheel side and nipped up the bolts. I then slide the timing chain end side cover on and measured a gap of 20 thou between the side cover and the gearbox/diff cover. Am I right in thinking that 20 thou minus crushed gasket at 7 thou equals 13 thou. Then this set up requires 4 thou preloaded so I need 9 thou of shims. Is that correct????

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#4 Thelowrider

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Posted 15 July 2018 - 06:25 PM

What type of bearings are being used on the diff if they don’t have ‘thrust’ on them then your looking at 2thou preload.

Do you already have shims in between the end plate and diff bearing if so you will need to remove 11thou of shims to get the required preload

Any further questions ask away.

Edited by Thelowrider, 15 July 2018 - 06:25 PM.


#5 germini30

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Posted 15 July 2018 - 06:29 PM

No shims at the moment, but these 3 where in before. Yes the bearings say thrust on them

#6 Thelowrider

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Posted 15 July 2018 - 07:05 PM

So your saying there is 20thou clearance between the output shaft housing and diff housing with no shims present?

If so something is wrong, are you sure the diff is full upto the other housing? Have you fitted the bearings, if so are they correctly seated?

#7 germini30

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Posted 15 July 2018 - 07:57 PM

With the diff all way to the right, diff cover on and right side cover fitted with a gasket the left hand cover pushes on to the housing and I have about 8 thou gap. No gasket on left hand side at the minute

#8 germini30

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Posted 15 July 2018 - 08:46 PM

Sorry I meant that it is. 008 thou

#9 Thelowrider

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Posted 15 July 2018 - 09:07 PM

That means you need a 3-4thou shim

#10 germini30

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Posted 15 July 2018 - 09:22 PM

Okay. I have three here that were fitted previously. One is like foil, next is like paper and the next is very stiff. No sizes written on them unfortunately

#11 germini30

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Posted 15 July 2018 - 09:23 PM

Must be 6,10 and 20

#12 germini30

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Posted 15 July 2018 - 09:35 PM

Sorry, should of said that the. 008 I got was with the three shims fitted

#13 Thelowrider

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Posted 16 July 2018 - 03:28 AM

If you have 8thou clearance with all 3 shims fitted then you will require another shim to get the required preload.

The preload needed for the bearings which have ‘thrust’ on them is 4thou this is why I asked whether or not it was written on the side of the bearing or not.

You will require a vernier ideally to see just how thick each individual shim is otherwise your just guessing S and when your trying to do something so accurately it’s not ideal.

Edited by Thelowrider, 16 July 2018 - 03:30 AM.


#14 germini30

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Posted 16 July 2018 - 06:24 AM

Thanks for the help. I read that you measure the gap then minus the gasket which is 7 thou so that would be 1 thou clearance, is that correct

#15 germini30

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Posted 16 July 2018 - 09:11 AM

The diff is pushed so far to the right that the crown wheel is touching the casing.

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