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MG Midget and Sprite Technical - Differential Pinion Shims

My diff is mid-rebuild -i.e fully dismantled. I have most of the parts I need either in hand or on order but, so far, I have not been able to source any Pinion Shims.

Moss and MGOC both list them but don't appear to have any available. I dropped in on AH spares yesterday but they don't even list them.

I've sent an enquiry to Heathrow Transmissions but not had a reply yet (it was after 5pm today).

Can anyone suggest any other potential sources who might be worth trying?

Thanks

Colin

PS - I've checked the archive but couldn't find any useful references to these shims.
C Mee

Hi Olin

Leacy classics have them in stock.
http://www.leacyclassics.com/catalogsearch/result/?q=ATA7039&cat=


Tony
Tony Brough

Tony,

That item is the sun gear thrust washer but they do appear to have the pinion shims http://www.leacyclassics.com/parts/austin-healey/healey-sprite/rear-axle-diff/37h7562.html and also do seem to list some of the diff carrier shims as well at bottom of page http://www.leacyclassics.com/parts/austin-healey/healey-sprite/rear-axle-diff.html?p=1

2nd link will have to be copied and pasted as the BBS has changed it to a https which doesn't work but http does.

Now I've edited it the BBS hasn't changed the link from http to https .
David Billington

Colin
Correct me please if I'm wrong but aren't they a collapsable sleeve setup for preload and if that's the case the only pinion shim would be for pinion depth,between the larger bearing and pinion head which for a rebuild you shouldn't need to change as it would have been selected originally to suit the case/pinion combo
If you are changing the pinion to another the original shim for the case is the one to use not the one that came with your pinion if it's a 2nd hand one
willy
William Revit

Colin

Guess you have seen Norm Kerr's diff rebuild tips: https://www.mgexp.com/article/mg-midget-differential-rebuild.html

Sprite Mania have some videos too: https://m.youtube.com/watch?v=H9yKWKV8poc

Sounds like you are getting ready for some great hillclimb standing starts!

Cheers
Mike

M Wood

Tony, David: Thanks for the links, I'll give them a call.

Willy: That thought had crossed my mind and I have to say I'm a bit confused by the combination of collapsible sleeve and shims. There's a new sleeve on order, so perhaps that will solve the problem.

Mike: Thanks for the links. I've seen Norm's video but, on this occasion, I've handed the diff over to a very experienced friend and I'm trying to make sure he's got all the parts he needs. You also got it in one! It's a 4.55 diff which should give me much better gearing for my local hill! In my first outing of the year last weekend I got within half a second of my PB which was a bit of a surprise given the weather conditions and the fact that the only thing I did to the car over the winter was paint one door!

Cheers

Colin
C Mee

Colin
ESM morris minors have the diff pinion shims, I bought a range last year , I was also rebuilding a 4.55 diff , IIRC they were also the cheapest supplier I found for diff parts.
Ian
Ian Webb 1973 GAN5

William,

I think you're wrong regarding the changing of the pinion into a different final drive case as that would require measuring the set-up again to determine the correct shim thickness to get the pinion in the correct position. The shim is to deal with tolerances of both the pinion and final drive case to get the pinion in the best mesh, I can't see using the case shim as reliable to get the correct mesh.
David Billington

Ian, thanks for that, not heard of ESM before but just had a look and they've got some really useful stuff.
John Payne

ESM seem decent and bought out or merged with the Bath MM spares place not that many years back when the owner retired. The Bath MM spares place were based just down the road from me, like less than 1 mile or previously about 1.5 miles. IIRC they split from Charley Ware in Bath many years ago and so the spares separated from restorations into separate businesses.
David Billington

David
The initial,original pinion height shim thickness is determined solely by measuring the case depth via a dummy pinion to get a shim thickness to suit a pinion with a lapped value of "0"
Therefor that shim thickness belongs to that case
Then if the pinion is marked with say for example plus 10 then that pinion has a lapped value of .010" and .010" has to be removed from the original selected shim thickness to set the pinion at the correct height
IF swapping to another pinion the values of the old and new pinions can be compared and the shim adjusted to suit
My point was that if you are swapping to a pinion from another housing,it's the shim from the housing that is used as the base,not the one that comes with the second hand pinion as that has been measured for a different housing.
Usually the pinion lapping No.s aren't far apart so the pinion can be fitted using the original housing shim without a problem but if you happened to have say a -5 and a +5 then of course a .010" shim adjustment would be needed
Usually there is only a couple of thou. if anything ,difference in pinion numbers so the original case shim is the go

Colin
Your confusion on shims could be caused by a previous rebuild
Your pinion should have the selected pinion height shim between the head of the pinion and the larger bearing, then the collapsible sleeve then the smaller bearing
If there has been a shim fitted in between the bearings with the collapsible sleeve it is a cheater ,used if you can't get a new sleeve- It's a fairly common practice to save money basically or to get out of trouble with an unavailable sleeve, to fit a packing shim in with a 2nd hand sleeve so that it can be retensioned to spec---quite ok but not ideal
Cheers
willy
William Revit

Ian: Thanks for the ESM link. It looks as though they've got almost everything I'm looking for to complete the shopping list. Sadly they're out of stock of the correct pinion thrust washer so I'm hoping the current one can be re-used, with shims if necessary.

Willy: Thanks for trying to clear up my confusion. I've got a new collapsible sleeve on order but I'll stock up on a set of shims anyway as it's a friend who's doing the re-build and I want to be sure he's got everything he needs to hand.

I've also got a spare 3.7 so I might pluck up courage and apply everything I've learnt from this thread and have a go at doing it myself! It has even more backlash than the one that's currently on the bench so I'm sure any extra shims won't go to waste!

Thanks

Colin
C Mee

Colin
I am with Willy on this one, I have read the post carefully, and you have not said you are not using the original case and pinion. There is a thrust washer, not a shim between the large bearing and the pinion, this is factory set, and should not be altered.

Dave
Dave Barrow

Dave, Willy: Thanks for the comments and advice.

The pinion and crown wheel are both fine and are being re-used along with the original casing. It's just the four bearings and any shims that are required that are being changed along with a new collapsible spacer.

The only item I've not been able to source is the pinion thrust washer so I hope there will be no problem re-using the existing one. Heathrow Transmissions replied yesterday saying that they do stock them but they also have a minimum order figure of £50!

I'll be handing everything over to my friend when I see him at the weekend and I'll report back when I have the finished diff back in my hands.

Cheers

Colin
C Mee

The trust washer is a solid lump, I should not think anything much could be wrong with it.

Dave
Dave Barrow

I wouldn't call the washer between the pinion and the bearing next to it a thrust washer but rather a shim as its thickness has to be determined by careful measuring of the pinion nose from the diff centreline and adjusted according to the value prescribed on the pinion determined by the manufacturer. Also there is no relative rotational movement between the bearing and pinion so that washer just takes up the space. Bearings are accurately made but it is possible for there to be enough difference between those that adding new bearings could require a different shim between pinion and bearing, worth going through the set-up procedure correctly as it is not difficult with the correct tools.
David Billington

Just to get this straight-

The washer between the pinion head and the main bearing - which in the parts list is named a thrust washer ,is in fact the shim for adjusting pinion height, which is as explained earlier selected "measured" to suit the case and pinion
It appears to be no longer available--
Having said that, anything can be made if needed--A shim is a shim, nothing else.
As David said, bearings are machined quite accurately and normally just for a rebearing job no shims are required-BUT it depends who's been in there previously
It'll simply be a case of put it together and measure it up, check the tooth pattern and reshim if needed
Your diff guys will sort it I'm sure

One little trick us old guys use is to put it together without the collapsible sleeve and seal and measure it all up,,change shims around if you have to and remeasure etc
Then when you're happy with it all pull it apart and do a final reassembly with the seal and sleeve fitted
Lots of people I know use bearing blue for checking tooth patterns just because the book says to but I've found some orange ochre mixed with a drop of oil is fantastic and leaves a really clear contact mark that is much easier to read than b/blue
We used redlead years back but almost impossible to get now
Good luck Colin, you've done all you can you deserve a good result
Cheers
willy
William Revit

This thread was discussed between 06/04/2018 and 11/04/2018

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.