Differential overhaul

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Declan_Burns
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Re: Differential overhaul

Postby Declan_Burns » Fri Oct 04, 2019 12:34 pm

I doubt if it would last until Christmas. The same thing will happen again.
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Declan


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Declan

philthehill
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Re: Differential overhaul

Postby philthehill » Fri Oct 04, 2019 1:00 pm

I am of the same opinion as Declan - leaving as it is and rebuilding is not the answer.
To get over the problem I would suggest filling the wear groove/lip with bronze weld and then grinding and lapping the carrier and washer together, you can then using an oversize thrust washer. It is going to take a bit of graft to get it back to a useable condition but it will be worth it and think of all that money you will have saved. :D

Finding a welder may be an easier option than finding a capable machinist.


ndevans
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Re: Differential overhaul

Postby ndevans » Fri Oct 04, 2019 1:21 pm

I did wonder whether it would be possible to fill the wear grove with weld! But surely I'd still need a machinist to clean up and smooth the weld?

Cheers N
cheers N
'69 Traveller, 1275, discs.

philthehill
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Re: Differential overhaul

Postby philthehill » Fri Oct 04, 2019 2:08 pm

If you are careful you can clean up the weld yourself with a burr/grindstone. Get the welder to only put as much weld to the wear as necessary. No need for overkill.
This will test your fitting skills :wink:


ndevans
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Re: Differential overhaul

Postby ndevans » Fri Oct 04, 2019 3:09 pm

Ha ha, that it will!

I haven't seen any dimensions or clearances for the sun/planet wheels. Do you know of any? For example, what should be the distance between the thrust washer surfaces on either side of the cage? What free play, if any, should the planet wheels have?

Cheers N
cheers N
'69 Traveller, 1275, discs.

philthehill
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Re: Differential overhaul

Postby philthehill » Fri Oct 04, 2019 5:01 pm

The Marina diff which is very similar to the Minor states ZERO (in capitals) backlash (no play). The manual also states 'at ZERO backlash it will be tight - lubricate before assembly'.
Therefore to answer your question I would go for ZERO backlash.

The Marina/Ital workshop manuals give far more detail than the Morris Minor workshop manual for both the 1098cc and 1275cc engines.
It also goes into far more detail on setting the axle diff and how to do the job.
It also gives additional torque settings that are missing from the Minor wksp manual.
The Marina/Ital factory workshop manual is a valuable addition to the repair & how to do it owners library.
I would not be without mine.

https://www.ebay.co.uk/itm/Genuine-Aust ... SwmTddQrM2


ndevans
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Re: Differential overhaul

Postby ndevans » Sat Oct 05, 2019 1:09 pm

Ok, here's the plan.

I'm going to chat to my local friendly machine shop, who re-bored my engine. I'll take the diff carrier and planet wheels down there, and explain in person what I want.

I'm going to ask him to machine or grind out the ridge around the centre hole, and the outer step, to the same level as the worn portion. I'm going to ask him to machine/grind it slightly larger than the diameter of the thrust washer.
I'm then going to ask him to clean up and smooth off the other end of the cage, and measure as accurately as possible the distance between the planet wheel centres along the shaft, and the distance from each side to the centre line. I'll also ask him to measure the depth of the machined area.
I'll then use oversize thrust washers and some valve grinding paste to lap then in and make them fit.

Does this sound a plan that will work?

Does anyone know what the distance between the back faces of the two planet wheels should be?

Cheers N
cheers N
'69 Traveller, 1275, discs.

pgp001
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Re: Differential overhaul

Postby pgp001 » Sat Oct 05, 2019 2:45 pm

Sorry I cannot help with dimensions, but as a machinist I would expect that job to end up quite expensive.

Machining a concave surface is difficult enough without it being on the inside face and difficult to get at, as Phil mentioned earlier it will require some special tooling to do that, and they probably will not have any without making it specially for this job.

Unless they are working at "mates rates" and it comes out very cheap, I would think your best option is to obtain another second hand diff or at least parts you need.
There is no shortage on ebay ( but no guarantee they will be any better either ).
https://www.ebay.co.uk/itm/AUSTIN-A30-A ... SwAGxdiIgl

https://www.ebay.co.uk/itm/Morris-Minor ... SwhEVdjiQs

Dont you already have a spare diff ?
I thought you had a 3.9 that you were rebuilding to replace the one from your car, maybe you could build one good one from the two.
I have not really been keeping up with the story, so am not sure which one you are working on.

Phil

ndevans
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Re: Differential overhaul

Postby ndevans » Sat Oct 05, 2019 5:34 pm

The diff I am working on is my spare, it's a 3.9:1. The 4.22:1 on the car is worn, and has probably had no attention since it was built, other than oil changes. I don't expect it to be much better when it gets stripped.

Cheers N
cheers N
'69 Traveller, 1275, discs.

paul 300358
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Re: Differential overhaul

Postby paul 300358 » Sat Oct 05, 2019 6:57 pm

I would have thought that the planet gear would revolve but the carrier and thrust would remain static. The fit would be more important than the grove as the two surfaces should not be moving much.

ndevans
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Re: Differential overhaul

Postby ndevans » Mon Oct 07, 2019 11:06 pm

Having ummed and ahhed about it over the weekend, I decided tonight to get the diff cage on my 4.22:1 apart. I was worried that it'd be as bad, if not worse, than the 3.9, but happily it appears not! The planet wheels had about 2mm lateral play along the shaft, which didn't bode well, and I was expecting a non-existent thrust washer on one end.
IMG_20191007_222504~2.jpg
Planet wheels, thrust washers, shaft and sun wheels from the 4.22:1.
IMG_20191007_222504~2.jpg (1.44 MiB) Viewed 358 times
IMG_20191007_222520~2.jpg
Thrust washer seat on one side of the diff cage.
IMG_20191007_222520~2.jpg (579.89 KiB) Viewed 358 times
IMG_20191007_222537~2.jpg
Thrust washer seat on the other side.
IMG_20191007_222537~2.jpg (567.94 KiB) Viewed 358 times
There is wear in the thrust washer seats, but nowhere near as bad as the 3.9, and not as bad as it looks. The wear is hardly noticeable when I run my finger over it. The shaft is worn, much like on the 3.9. The bearings are a bit more worn than on the 3.9, but I'm loathe to pull them off and replace, as I don't have the special tool and gauge block that goes with it.
The only other thing is that the sun wheels don't have the fibre washer under them that the ones on the 3.9 do. I wonder if that would account for some of the play of the planet wheels along the shaft?

So my current thoughts are that I'm better off replacing the shaft and thrust washers, and oil seal, on the 4.22, putting it back on the car, and carrying on with it until I've either sorted the 3.9, or sourced one with a good diff cage.

Cheers N
cheers N
'69 Traveller, 1275, discs.

pgp001
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Re: Differential overhaul

Postby pgp001 » Tue Oct 08, 2019 12:02 am

When you took the 4.22 apart was it evident where all the prop shaft free play was coming from shown in your original video ?
Was it purely due to the 2mm lateral movement of the planet wheels ?

Can you not build your 3.9 up using the good cage from the 4.22 ?

Phil

ndevans
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Re: Differential overhaul

Postby ndevans » Tue Oct 08, 2019 12:07 am

Not sure, might just be wear between the pinion & crown wheel. The splines on the sun wheels, which are what the half shafts locate in, look ok. Some of the play might be the wheel bearings, which were loose in the hubs.

Unfortunately, the diff cage on the 4.22 is an ATA type, on the 3.9 it's a BTA. Not sure what the difference is, but apparently they are not interchangeable.
cheers N
'69 Traveller, 1275, discs.

don58van
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Re: Differential overhaul

Postby don58van » Tue Oct 08, 2019 2:36 am

Not sure what the difference is
My understanding is that the cage is stronger (thicker construction?) but that doesn't necessarily mean that they are not interchangeable. Does anyone on here know?
Don

philthehill
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Re: Differential overhaul

Postby philthehill » Tue Oct 08, 2019 7:44 am

As I have previously stated the ATA and BTA carriers are not interchangeable. There are differences in the carrier that do not allow the interchange.
To confirm the above statement I have just looked at various MG/Sprite articles/publications regarding the interchangeability of the differential parts and all state that the carrier is not interchangeable between ATA and BTA units. They also state that problems arise with the interchangeability of pinion, pinion bearings and spacer.


don58van
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Re: Differential overhaul

Postby don58van » Tue Oct 08, 2019 9:00 am

As I have previously stated...
Ooops :oops: :oops:

Sorry Phil. I didn't remember reading that. But then I can't remember what I had for breakfast.

D

ndevans
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Re: Differential overhaul

Postby ndevans » Tue Oct 08, 2019 9:56 am

Are the sun and planet wheels interchangeable? They look it, and the ones off the 3.9 are in better nick.

Cheers N
cheers N
'69 Traveller, 1275, discs.

philthehill
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Re: Differential overhaul

Postby philthehill » Tue Oct 08, 2019 10:46 am

According to the Moss web site they are interchangeable as they have the same part numbers for both the 1275cc and 1098cc axles.

Sun Wheel Pt No: ATA7037

Planet gear Pt No: 2A7037


pgp001
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Re: Differential overhaul

Postby pgp001 » Tue Oct 08, 2019 12:57 pm

Phil

Just for future reference, would you clarify the significance of the ATA and BTA designations please.
I have not come across this before and would like to know how to recognise the difference when looking at spare diffs.

Thanks
Phil

ndevans
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Re: Differential overhaul

Postby ndevans » Tue Oct 08, 2019 2:12 pm

It'll be stamped ATA or BTA on the rim of the crown wheel. I think the outer casings are all ATA, but the cage & crown wheel assembly is either ATA or BTA.

I think, but not positive, that the BTA carrier was fitted to Midgets and Wolseleys.

Cheers N
cheers N
'69 Traveller, 1275, discs.


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