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MG MGA - Diff Pinion Seal

I need to replace the diff pinion seal on my MK 2 but cannot remove the nut holding the drive flange.

It is a castelated nut with the crown peened over the end of the threads and I cannot get an edge in order to straighten the crown,

Is there any method in undoing these nuts.
G Hamilton

I'm not exactly sure what you mean when you say the "crown is peened over the end of the threads". Normally castelated nuts are used with cotter (split) pins. I don't recall if there is a cotter pin here or not. If there is, it should be removed. I'd use a big pipe wrench to hold the flange, and a breaker bar with a piece of pipe to extend it for leverage. I'm pretty sure you'll be able to remove the nut even if the thread is buggered. One of the high torque impact wrenches would probably also do it. If the peened over surface is really a problem, get a die grinder or dremel tool and grind it.
G T Foster

I cannot answer that aspect of your problem, however, you may be interested in the home-made flange steady I made, so that I could get the torque on the nut. I claim no credit for the idea. It was described to me by someone else on this BBS - from Oz I think.

Will not brute force remove the nut or do you think that will damage the thread? You can see from the photo that mine is not castellated.


Steve Gyles

I replaced the pinion seal on my A this past summer, but unlike your situation, my pinion nut was barely hand tight. My pinion nut by the way is a thin, but otherwise standard nut. The DPO apparently didn’t want to fiddle with the pinion spacer shims so he just put a little compression on the lock washer and called it good. As you can see from the attached picture, the shims did not fare well. When I replaced the shims I could not come up with anyway to measure what was needed to take out the play so it was trial and error. If you do have to install new shims, don’t install the new pinion seal. The shims fit behind the front bearing but in front of the distance piece. Do all the fitting, which includes tightening the pinion nut to take out the play, to get the right combination of shims. Once you know the correct combination of shims you can then assemble everything, including the new seal.

Pictures and more explanation on Barney’s site, . I purchased the full range of shims from Moss, all had the proper OD. I recall using a combination of the thickest and one other shim. The pinion nut torque is something like 150 ft.-lbs., so breaking it free will be a challenge. I used Steve Gyles’ set up for test fitting the shims and when I finally retighten the pinion nut.

Good luck,


jjb Backman

Thanks guys I have made up a flange steady today and will borrow a a "rattle gun" (torque wrench) and give it another go over the weekend.

G Hamilton

If your only problem is that the seal is leaking and everything else is working OK. Mark the end of the shaft and the nut with punch marks next to each other. (One on the shaft, and one on the nut.) Then when you reassemble just tighten until the punch marks line up again and you will be assembled just like it was before you changed the seal.
Ed Bell

Thanks Ed I had already done that when I pulled the drive shaft and yes it is only a leaking seal, everthing else is fine.
G Hamilton

When the pinion nut is tight with a new seal and the shims are corect it should take 7 inch lbs to turn the pinion flange. When setting up the pinion shims without the seal it is 4 inch lbs. Use a balance sv=cale hooked into one of the bolt holes and it should read a fraction lower than 7.
Garth Bagnall

Got the job done today and what a revalation, the nut came undone with the help of a steady and much grunt from a air driven torque wrench.

When I got the seal out it had gone brittle and was as hard as a rock and had lightly scored the pinion shaft which cleaned up pretty well with sand paper whilst using the lathe.

Thanks for all the advice and now onto another oil leak this time the speedo cable oil seal in the gearbox which Barney has covered.
G Hamilton

I had ordered a pinion seal for this job from Moss USA and received a seal with a 1.5" ID and 2.5" OD and a width of .375".

This seal did not fit my MK2 axle as the OD on my diff is 2.375". Moss claim to have sold hundreds of these seals without complaint. My question is were there 2 differant diffs around.
G Hamilton

Good question, but maybe no answer. There was a change of factory part number for the pinion seal from ATA7040 to 88G320, but that was a change of materials and construction of the seal, not the installation dimensions. Today's replacement seals are likely different construction again, but still fit the same dimensions.

I have been using these seals from Moss for years. Last time I bought two in February 2006. I installed one and still have one in stock. They are 2.510" OD, and they do fit. To best of my knowledge, there was never any change of design of the differential carrier housing for the Austin B-series rear axle, 1953-1967.

So now the question is, how did you happen upon a differential carrier with a smaller OD for the pinion seal?
Barney Gaylord

I have spoken to Garry Kemm re CKD Assy in Oz and he says the diffs were standard axles from the UK and already assembled and with the 2.5" OD so it seems I must have a differant diff centre from where I don't know.
G Hamilton

This thread was discussed between 05/04/2010 and 09/04/2010

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