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MG Midget and Sprite Technical - Pinion seal, preload, nut torque

I have the axle off the car and on a stand. With a bag of nuts and bolts, string, and maths the torque to turn the pinion end of the differential is measured at 6.4 lb inch. That’s with the axle fully assembled and the drums off.

Reading through old threads that’s just within the 4 to 6 lb inch figure for a worn in bearing.

I marked the nut’s position relative to the shaft. Drilled some steel angle to hold it in place and then set about to undo the nut which should have been at around 100 to 140 lb ft torque.

It was undone really easily at about 120 lb inch which is way too low and risks undoing?

So do I tighten it up to original position plus a bit to say a preload of 6 lb inch, is that likely to give a sufficient nut torque?
Or do I need a new collapseable spacer?

With a new spacer do I just retighten to 6 lb in bearing preload? Is there anything else to consider?

C MADGE

IIRC when I helped my neighbour set-up his new CWP in his Morgan the pinion pre-load torque is checked with the crownwheel and diff assembly removed so you are only checking the pinion torque not the whole assembly.
David Billington

Sorry there’s a typo in my original post, the torque to turn the pinion is 4.6 lb inch which is on the low side but just within the 4 to 6 figure I have seen mentioned for a worn in differential.
C MADGE

Yes, I believe you are correct, David - just the pinion.

I’m sure I’ve also read something about the oil seal giving a false reading.
Dave O'Neill 2

I might well be wrong but this subject seems familiar, was it covered recently in another thread or am I on dreaming again.
Nigel Atkins

Dave,

In the case of my neighbours Morgan the axle was a Salisbury type and the same basic axle was used on a Winget dump truck and the axle manual is available online for the Winget. It gives all the set-up procedure and quoted torques for just the pinion, the additional torque with the diff, and the additional torque with the halfshafts in. The A series axle is different in design but the same principles apply so ideally one can find the details for the A series axle and work accordingly.
David Billington

A few internet sources that I looked at suggest the pinion preload torque is 4 to 6 lb inch with just drums off
http://mgparts.co.nz/diff-pinion-and-oil-seal-replacement/

And

http://www.mg-cars.net/mg-midget-sprite-technical-bbs/diff-pinion-seal-2012102018161317478.htm

The Haynes manual says tighten nut up to 140 lb ft which risk over compressing the spacer and too high preload.
C MADGE

When I did my overhaul, the pinion preload was done with the crown wheel fully assembled. With the half shafts out, I would think that the drag on the pinion from the crown wheel would be negligible.
Its been fine for several hundred miles now.


Dave
Dave Barrow

Norn Kerr's helpful piece:
https://www.mgexp.com/article/mg-midget-differential-rebuild.html
Graeme Williams

This thread was discussed between 28/06/2018 and 01/07/2018

MG Midget and Sprite Technical index

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