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MG TD TF 1500 - TD Differential

Well, I guess we've done it now. The rear axle on Peter's TD 10879 was making a pretty loud whine so he decided to investigate. We've discovered that the pinion (crown wheel) moves in and out about an eighth of an inch and has about 4 degrees of free rotation. Peter believes that shortening the preload spacer (WSM # 23, Moss # 38) just a bit will eliminate the excessive in/out movement. Cederstrand seems to say the same thing but I admit that the mechanics of all of this is a bit beyond me. Any thoughts or suggestions will be appreciated.

Peter also believes that the ring gear is a bit to far toward the left side of the diff. There was no gasket (WSM # 4, Moss #47), just some sealant so adding the gasket would increase that offset albeit just by a smidge. Peter plans to fabricate new spacers (WSM # 18, Moss # 32) to move the ring gear just a smidge to the right. Again, any thoughts or suggestions will be appreciated.

I've searched the archives and all the threads are about people changing the rear end gearing to a taller gear. We've downloaded Cederstrand's excellent work and plan on following it.

Thanks.

Jud


J K Chapin

Jud
For the pinion to have that much movement, something has happened there, shortening the spacer isn't the answer
Two choices,

either one of the pinion bearings has packed up,

or maybe it was the pinion nut itself came loose


There's nothing else that can cause it if it had previously been ok
William Revit

Jud, as mentioned above do not change the length of the spacer. It sets the position of the pinion head and this must be correct for the diff to function correctly. Also do not touch the position of the ring gear until you have the head of the pinion in the correct place with the correct preload. Only then can you measure the lash between the pinion and crown wheel and, in the unlikely event, that it need adjusting then you can add or subtract shims. Don't forget that the differential bearings require a bit of "crush" or actually preload as set out in the TD workshop manual.
Cheers, Hugh
H.D. Pite

Oops! I confused 0.008 with 1/8. Here's the correction:
Jud,

The pinion moves in and out about 8 thousands, (not 1/8"). And that is with a tight nut.
I just made a little gauge. It appears the pinion also needs to move towards the ringgear about 1/16". (0.015").
I had some good response from Eddie. He says to adjust the ringgear , the spacer rings behind the carrier bearings need to be changed Those are the 1/2" spacers we measured.

this is what I need to do next week:
1. Make a 1/16" thick shim to adjust the pinion
2. Shorten the sleeve between the 2 bearings by about 0.008"
3. Make 2 new bearing spacers. I am figuring out right now, how thick they need to be.
J K Chapin

1/16” Sounds extremely excessive. Don’t mix up the existing side load shims making sure they stay on the same sides of the carrier they were removed from. Also. If the gear set is whining loudly at this point it may not be possible to lose the whine. As the tooth contact pattern is likely to be worn
W A Chasser

How did you make a gauge to determine the position of the pinion head? The factory gauge is not a trivial special tool.
Here is what I would do:
1. replace the pinion bearings
2. with the pinion nut tightened, check the preload.
3. adjust 2. by using shims against the spacer or take the spacer to a grinding shop to shorten it slightly (you will not be able to do this satisfactorily at home).
4. note that there is another spacer (pinion adjusting washer) between the inner bearing and the pinion head. This is what sets the position of the pinion head. I can not see how this position has changed since there is no possibility of wear on it.
5. check the crush on the differential bearings.
6. with the correct crush check the lash between the pinion and crownwheel. If not correct, adjust as set out in the TD WS manual.
The sequence is similar as to what is set out in the Cederstrand manual. Success will only be realized if the sequence is followed.
Hugh Pite (who has done a number of these)
H.D. Pite

Hugh, thanks. Here's Peter's response. I think y'all are on the same page.

ps: the fog and driving lights are great!!

Jud,

I'll answer these questions, just in case you want to pass this on.

I made a gauge from 3/16 thick Aluminium sheet, in kind of a "Z" shape. The bottom leg is perfectly flat and can be held against the end of the pinion. The other leg of the "z" extends to the bore of the carrier bearing. With a fine file and a micrometer, the distance from the bottom of the "z" and the tip of the other leg of the "z" (measured perpendicular) was made exactly to the dimension (0.959) of Cederstrand's write up on Page 40. The gauge was short of reaching the left side of the bore of the carrier bearing by approx 0.015". The lack of a spacer behind the pinion and the inner bearing explains the discrepancy.

1. The pinion bearings are fine and need no replacement. I think they were replaced, but they (whoever they may be)never added a shim nor tested the position. It was obvious that some previous owner had the differential disassembled and put it back together without knowing what he was doing. Not to forget, I found some ground up metal pieces in the case.

2. yes
3. yes
4. This spacer is currently non existent.
5. Yes
6.Yes

Given the irregular wear of the pinion (also but to a lesser degree to the crown gear) caused by the fact that it had been installed without any preload , actually it loose and had 0.008" axial play, there is no sense to make proper adjustments now, other than adjusting the preload on the pinion bearings. Installing everything according to the factory specifications will at this point only cause more damage. I will run this thing till destruction and then install new gears. I expect and hope it to last a few years. I hope that "fixing" the pinion bearing adjustment will lower the noise level, because the pinion will at least run true.

Peter
J K Chapin

Peter, this spacer is absolutely necessary to get the position of the pinion head in the correct position. MOSS sells a selection of 18 different sizes - Moss number 266-050 t0 266-160. I wonder if this pinion head spacer not being in place is the cause of all the problems?
Maybe a good time to put in some MGA 4.3 gears?
Cheers, Hugh
H.D. Pite

Unfortunately, my Moss catelog indicates that none of the spacers are available. I'll check with Abingdon Spares.

Jud
J K Chapin

Jud did you check out Rear End Virgin Conversion? Good article on the topic. I purchased the necessary components from B&G and had a firm here in Sydney who specialize in differentials do the work, as I wasn't prepared to proceed without the essential measuring gear. The 4.3 that Hugh suggests is a great move and takes a load off the engine when traveling at highway speeds. Also worth noting that the early M.G. B C&P is also a 4.3 and can be fitted to the TD. Cheers
Peter TD 5801
P Hehir

Jud,
I have an alternative way of measuring pinion depth using a precision set square and a bore gauge.
Regards
Declan

Declan Burns

Declan, that looks like a very elegant and precise way of measuring the pinion head position.
Cheers, Hugh
H.D. Pite

Thanks Hugh,
It gets around complicated measurements very easily.
Regards
Declan
Declan Burns

We went to a friend's garage today and bought his used pinion and ring gear. We inspected the pinion fairly thoroughly but, alas, gave the ring gear only a cursory inspection. Back home on closer inspection we found serious pitting on the back side (not the pressure side) ring gear. The pressure side of the teeth look much better although I don't have a picture to post.

1. What would cause this kind of pitting?
2. Is it good for anything other than a paper weight?

Thanks.

Jud

J K Chapin

I have a 4.875 CW&P in good condition from my TF1500 when I changed it over to a 4.3 from an MGA. Give me a call if you're interested in purchasing, we can probably agree on a price.
Phone 514-946-2445, email thomasw.moore@yahoo.ca if you're interested. I can email photos to confirm the condition.
T W Moore

Well that’s junk!
W A Chasser

That looks like a case of severe cavitation to me. Bin it.
Regards
Declan
Declan Burns

I agree Declan
We tried running thin oil in the rear axle of a racer once and exactly that was the result
Apparently it's caused by the oil getting too hot and almost bubbling/frothing and can be from too thin a oil, contaminated oil(water), or too high an operating temp caused by many possibles like too much power on a small diff , too little backlash, even a way out of balance tailshaft
Most likely in this case would have been wrong or low oil or water contamination
What condition were the coast side of the pinion teeth in Jud. -just out of interest

willy
William Revit

Yes indeed - junk it and search out some 4.55 or 4.3 gears to make driving much more enjoyable.
Hugh Pite
H.D. Pite

Well, this morning we picked up bare chassis 20878 (October, 1952). This afternoon we took the rear axle apart and found that the pinion and ring gear (in fact the whole differential) appear to be in pristine condition. Things are looking up for TD 10879.

The pic attached shows the front suspension. I don't know if the shocks are original. I think they are Armstrong. The chassis, although bearing a bit of surface rust, appears to be perfectly square. I suspect that the red front springs and possibly the lower A-arm pans are aftermarket but I certainly don't know.

If anybody wants a good chassis, this one is available.

Jud

ps: I also picked up a red upholstered TD seat back in very good condition. It's also available if anybody is interested. Pictures available on request.


J K Chapin

This thread was discussed between 19/04/2020 and 24/04/2020

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