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Differential, Installation procedure

"No shims necessary!? Unlikely."

Procedure for installing standard diff:

Now on to finding the correct shim:

Key Meaning
A Your measurement.
X Shim (pack) thickness.
0.001 Minimum preload.
0.002 Maximum preload.
0.007 Compressed gasket after torque down.
Xmax 0.001" + 0.007" - A
Xmin 0.002" + 0.007" - A

And some examples:

Your measurement Xmax Xmin
0.005" (0.001" + 0.007") - 0.005" = 0.003"
(0.002" + 0.007") - 0.005" = 0.004"
0.008" (0.001" + 0.007") - 0.008" = 0"
(No shim needed)
(0.002" + 0.007") - 0.008" = 0.001"
(Don't bother)
0.010" (0.001" + 0.007") - 0.010" = -0.002"
(Not possible)
(0.002" + 0.007") - 0.010" = -0.001"
(Not possible)

In the third example, you probably have done something wrong, like not pushing over enough in the first step above, or there is a mismatch of components.

Now if you're picky, you may install the shims and then measure again. Then you should come up with 0.008" to 0.009". I would go for 0.009" to get max specified preload. As the bearings are run in, they will loose some preload. I prefer high preload, as no preload makes sounds, wears down bearings and make it more prone to piss oil.

What may have happened to you is:

If you assemble the whole shebang and torque down the casing nuts before the end covers, the casing will pinch the bearings. Then as you torque down the end covers, they will push the diff and bearings over to the side away from the cover that has no slack against the bearing. The other cover will have air between it and the bearing, but there will be preload. Until the differential assembly gets a sideways force that overcome the pinching force of the cover that is. Such forces may be a result of the helical pinion, or your hammer blow.

OK. All that aside. It is *not* this setting that make your inner flange wobble!

That is the play of the cylinder shaped part of the flange in the bushes of the end cover. Did you check this? What Haynes says is to "fit a new cover". (Thank you Mr. Haynes! Got any stock in the spare parts dept.?) The play in the differential gear shafts in the diff cage bushes also affect the sloppiness of the shafts, although they seldom are very worn down.

What you should do is not reinstall parts that does not have a good fit when you put the flange into the cover. Alternatively to grind down the flange until all wear is taken out, then fit and ream new bushes to the end cover. Oilways must also be carved into these bushes. To my knowledge you cannot buy the needed oversize bushes, and need to make them yourself.

If the fit is sloppy, then your inner CV's will also slop. And the seals will be left with an impossible task, so they will let oil out onto your driveway.

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Differential shim preload

"I now understand the 0.002" bearing preload which previously I could only visualize as a 0.002" space. DOH. Well at least I finally get it now.

Regarding preload, I wasn't sure how much to shim as my measurements were ambiguous. While a 0.012" feeler gauge would fit between the end cover and the diff. cover, only a 0.006" would fit between the end cover and the gearbox casing. This was with two 0.020" and one 0.012" shim in place and no gasket.

I figured this was going to be the best compromise I could reach. However, I feared that on the 0.012" side I was over-shimmed. However, my father's opinion was that since the output shaft can be finger-turned with the end cover torqued into place, it's probably not excessively preloaded."

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Differential drive ratios - what's yours?

(See also Final Drive)

Diff Ratio
New 5-speed Cooper
City E, HLE, Mayfair (82 - 85, 998cc, 10" wheels)
Pre 82, 10"wheels
3.44 or 3.76
Economy 998cc, 12" wheels, Rover Cooper, Metro Turbo
3.1 or 3.2
998cc Automatic
3.3 (tbc)
998cc Automatic (from Jim Harwood / Mini Workshop Manual)
998cc Manual (from Jim Harwood / Mini Workshop Manual)
Damn quick (MG Metro, Cooper, GT etc)
Old 850s, Pickups etc (screamers)
3.76 or 4.1
updated January 1, 2003

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Differential unit swap

Some say this can be done with the engine in the car, but this will require:

Assuming engine out...

It is a major job (engine out, box off, box in pieces) but something the DIYer can do. If you take your time and do it properly and carefully then there is no reason why it shouldn't all work ok afterwards. Gearboxes look terrifying at first but once you know how it works and how to dismantle and re-assemble one they are easy.

The good news is you don't need to remove and dismantle the mainshaft (the nasty bit).

You will need to:

Assembly is the reverse of removal!

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Footer SSI Insert revised: 23-Feb-2016