Page 1 of 11

Differential overhaul

Posted: Fri Sep 13, 2019 11:24 pm
by ndevans
As I'm going to strip and overhaul my spare 3.9:1 diff, which is going to replace my worn 4.22:1 diff, I thought I'd start a thread for it. You never know, someone else might find my learning journey useful at some point. I'm sure someone will have posted similar before, but there's no harm in adding to the knowledge on here.

At this stage, I'm only intending to replace the oil seal and possibly some of the pinions in the cage. I don't really want to go down the road of setting up the crown wheel-pinion indexing properly, which I will have to do if I change the bearings, and as they seem ok, I'm probably going to leave them alone.
If just the oil seal and cage pinions are being replaced, then as long as everything is marked and goes back together exactly as it was, there should be no need to reset the pinion-crown wheel indexing.
I have marked the bearing caps where they mate with the casing, and marked the flange nut and flange, so that all can go back as it was.
It was a struggle, but I've got the bearing caps off. Getting the cage out was not easy, but fortunately I managed to mount the diff on the engine stand, which meant I could stand on the frame and get my back into it. Eventually it came free. Cage dismantling starts tomorrow.

Re: Differential overhaul

Posted: Sat Sep 14, 2019 2:25 am
by oliver90owner
The beginnings of another epic saga? I like your optimism that all seems OK. I usually prepare for the worst scenario and anything better than that is considered a bonus. :D

Re: Differential overhaul

Posted: Sat Sep 14, 2019 7:33 am
by ndevans
:lol: :lol:

Hopefully not too epic. I think at least one pinion need replacing, but apart from that I'm hoping it'll just be a good clean, and the oil seal that needs replacing.

Re: Differential overhaul

Posted: Sat Sep 14, 2019 10:27 am
by alanworland
Good luck, years ago I rebuilt a Triumph diff which was going to be seals, nothing major.
However! when I had it all apart I ended up replacing all bearings as while they felt ok and smooth when I actually examined them the roller surfaces had started to break up.
Without new bearings it wouldn't have had long on this earth!
Don't remember it being that bad a job setting it up.

Alan

Re: Differential overhaul

Posted: Sun Sep 15, 2019 8:50 am
by MikeNash
I look forward to following your adventure in diffs, Alan!

Just a thought; long ago and far away I was helped in adjusting a spiral bevel axle on a Morris 10 (of about 1935) by some old fitters. (One had started as an career in the RAF, that is the Royal Aircraft Factory and pre the Royal Air Force!) They used Rizla cigarette papers as a guide for getting the right clearance between the gears because these papers have very tightly controlled thicknesses. Thus the "Blue" ones are one and an eighth of a thousandth of an inch thick, the "Silver" are one thou thick and the protective sheet inside both is one and a half thick. (The colour refers to the cover - there are other colours of different thicknesses I've not used recently.) If the paper was cut as it went though the gears then the clearance was less than the paper thickness. (Note, my micrometer only measures in thousands; I'm interpolating below that.)

Of course, the Minor has a hypoid axle with some scrubbing action, so I'm not sure of the above's applicability - but it might help! The dodge was a bit quicker to getting the clearance right than just using engineer's blue on its own.

Regards from MikeN.

Re: Differential overhaul

Posted: Mon Sep 23, 2019 11:21 pm
by ndevans
My 3.9:1 diff mounted on my engine stand. The diff flange is fixed to the engine stand using several pieces of angle 3mm thick. The angle is bolted together, and to the engine stand, using M8 threaded rod.

Getting the flange nut off is proving tricky. I have the correct size 1/2" drive socket, and a long socket wrench, plus a long piece of scaffold to use as an extender. There is a lot of movement when I try to undo it though, and I'm worried that the M8 threaded rod will break. The angle is strong stuff, and shows no sign of bending or breaking.

I'm interested to know how others have secured the diff flange to remove the flange nut? Do you do it with the diff still on the car?

Cheers N
IMG_20190923_222311~2.jpg
IMG_20190923_222311~2.jpg (1.45 MiB) Viewed 1561 times

Re: Differential overhaul

Posted: Tue Sep 24, 2019 7:02 am
by Banned User
I’ve just acquired a diff to strip for rebuild, I used my impact gun to get the flange nut off in a jiffy. Obviously I’ll need a different arrangement to refit it properly.

Re: Differential overhaul

Posted: Tue Sep 24, 2019 7:10 am
by ndevans
How did you secure the flange, if it wasn't on the car?

Re: Differential overhaul

Posted: Tue Sep 24, 2019 7:30 am
by Banned User
The way an impact gun works means that you can hold most things by hand.

Re: Differential overhaul

Posted: Tue Sep 24, 2019 9:29 am
by ndevans
Ah, i don't have an impact wrench.
Did it leave the nut intact, and re-useable?

Re: Differential overhaul

Posted: Tue Sep 24, 2019 10:30 am
by Banned User
Absolutely, they don’t damage stuff, it just sounds like it might.

Re: Differential overhaul

Posted: Tue Sep 24, 2019 11:58 am
by Declan_Burns
I made my own tool for holding the differential flange. These are laser cut from 8mm BMS and I have a few of them.
Regards
Declan

Re: Differential overhaul

Posted: Tue Sep 24, 2019 12:55 pm
by ndevans
Looks interesting. Is that a bar, one end of which bolts to the flange, the other resting on the floor, while you use a socket and wrench to remove the nut?
My diff is not in the car, but I am beginning to think that the way forward is to fit it it the axle, mounted on the car, brace the flange against the floor, and use a socket wrench and extender bar on the nut.

Re: Differential overhaul

Posted: Tue Sep 24, 2019 2:48 pm
by Declan_Burns
Here's another method with the diff off the car.
Regards
Declan

Re: Differential overhaul

Posted: Tue Sep 24, 2019 2:59 pm
by ndevans
I tried something similar, with a piece of 3mm angle bolted to the flange, and held in the vice jaws. I don't think the surface that my vice is bolted to is strong enough to resist the turning force! I think it will splinter!

Re: Differential overhaul

Posted: Tue Sep 24, 2019 3:01 pm
by ndevans
I've also thought about bolting a piece of angle to the flange, then bolting the angle to a thick piece of wood, in turn screwed firmly into the concrete garage floor.

Re: Differential overhaul

Posted: Tue Sep 24, 2019 3:06 pm
by Banned User
Got a friendly local tyre fitter? They'll have an impact gun.

Re: Differential overhaul

Posted: Tue Sep 24, 2019 3:28 pm
by philthehill
Plenty of new and used air impact guns on 'e' bay which can be purchased without breaking the bank.

Declan
Nice to see a pair of vice jaw protectors in use. That vice looks to be really useful and heavy duty.

Phil

Re: Differential overhaul

Posted: Tue Sep 24, 2019 9:16 pm
by ndevans
Gotcha!
IMG_20190924_211218~2.jpg
IMG_20190924_211218~2.jpg (1.6 MiB) Viewed 1472 times
An hour of "persuasion" with my two largest wrenches did the job. I was worried I was going to break the vice at one point, but finally it came loose. I said I'd give it until 9pm, then knock off, and at spot on 9pm it came loose!

Is the dust cap meant to separate from the flange, or is it all one piece?

Cheers N

Re: Differential overhaul

Posted: Tue Sep 24, 2019 9:29 pm
by Banned User
Well done. Dust cap is separate.