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MG Midget and Sprite Technical - diff looses oil

Hi there

The diff throws oil out while spinning. I can see the oil on the bottom of thje car

Anyone an idea how to solve this?
a.o. arnold

pinion seal, I guess?
David Cox

OK, is that doable as a DIY?
a.o. arnold

did mine some years ago but had the benefit of putting the car on a lift. Wouldn't fancy tackling it otherwise. The pinion nut is done up 140 ft lbs IIRC
David Cox

Unlikely but worth checking as it's so easy to do - the breather valve isn't blocked, the top cap pulls off and the riser body unscrews. The modern ones are plastic, I don't know if they always were.
Nigel Atkins

I replaced my pinion seal with the axle off the car, but I have heard of people doing it with the axle on the car. If I had to do it with the axle on the car, here is how I would tackle it:

Lift the car onto axle stands - you will need enough room to maneuver a breaker bar for, say, 1/4 of a turn. The car needs to be very secure on the stands, as the pinion nut can be tight.

Disconnect prop shaft

Make a long bar you can bolt onto the pinion flange with the other end resting against something solid to stop the diff turning when undoing the pinion nut.

Mark the position of the nut WRT to the flange. Undo, dismantle, replace seal, and tighten it back up to exactly the same place as indicated by your mark. Ideally you should check the pinion pre-load with a torque wrench and reset it with a new crush washer if required.

Reconnect prop shaft.

That is from memory, I *think* i have covered everything.
Chris Madge

I have done it, as Chris drscribes. The only thing I would advise is that you set the long bar that acts to stop the pinion turning so that it wedges against the underside of the car (with suitable packing / load spreader) If the end of the bar wedges on the ground, when you begin to pull hard on the breaker bar it will try to dangerously lever the car off the axle stands.

I don't have one, but I imagine a hammer action automatic torque gun might make undoing the nut easier.

There's a lot said about setting pinion pre-load and use of crush spacers, but if all you are doing is removing and replacing the seal, and don't disturb anything else,then its a straightforward job. Just tighten the nut up to the same position it was at before, using your marks as a guide.
GuyW

Inspect the pinion seal surface for wear. After maybe 60 years it will probably be beyond redemption. You can fit a Speedi-Sleeve to sort that out.

Les
L B Rose

Best to mark the nut and pinion shaft rather than the flange as the flange can go back in multiple positions AFAIK.
David Billington

What David says about marking the nut and pinion.

I have actually undone the pinion nut with the rear wheels on ramps and my (now late) father standing on the brake pedal.

These days I would use my trusty length of angle iron, which has two holes drilled in it, so it can be bolted to the flange.
Dave O'Neill 2

What Guy says about the chatter-gun. Mine's a cheap one that works off a 12v battery.
Absolute godsend.
Whizzed the crank centre nut off a 1275 and the wheelnuts off a Defender without breaking sweat and I think some of the fancier types can be set for desired torque for reassembly, although that might not be necessary as Guy says.
PS. I liked Nigels idea of checking the breather first. Simple to eliminate.
Greybeard

I had a drip onto the garage floor, mild but consistent. I recently changed fluids in both the B and the midget. Prior to draining the diffs, I removed the fill plugs. The Midget was overfilled and fluid ran and ran before leveling off. I drained it and replaced it, being careful to let it drip completely prior to replacing the fill port.

Being overfilled was the problem as it hasn't dripped a drop since.
Glenn Mallory

I'll order a seal and give it a try
a.o. arnold

So, I did all that was recommended. Marked everything etc...

BUT the nut was no tight at all.

So now I will renew the seal but it does not make any sense to tighten according the marking.

What to do?
a.o. arnold

Then it sounds like you need to check the pinion bearings and make sure they are not excessively worn.

If they are ok, you need to tighten up the pinion nut to achieve the correction bearing preload. I cant remember the figure exactly, but when i was looking there were a few figures quoted based several states (with or without halfshafts) etc.

I'm assuming your diff has the crush spacer. You will need to check the pre-load torque frequently as just a small turn on the nut will change the figure dramatically. Go too far and you will need a new crush spacer.
Chris Madge

Hi Chris

Thanks. Is this DIY or am I entering the limits here?
a.o. arnold

The pinion nut torque is 140 ft lbs BUT the pre-load measured at the flange should be in the range 6 to 10 inch lbs, repeat INCH LBS. This can be measured with a spring balance at a suitable radius. 140 ft lbs is TIGHT. You have to gradually tighten the nut, with the flange suitably restrained and keep checking the pre-load. So maybe go to 100 ft lbs, check pre-load, if too low go to 105, check, 110, check and so on. Difficult under car I imagine, without a pit or ramp, to get the high torque figure.
Bill Bretherton

Its definitely do-able at home. I didnt have a suitable torque wrench that went that low so i used maths, string and a weighed bag of bolts to calculate the preload torque.

I did mine with the axle off the car, and Bill also did his off the car. I'm not sure how practical it will be under the car though. If you do try it under the car you must be careful putting that much torque through the pinion nut whilst the car is on axle stands.
Chris Madge

Can someone confirm the diff oil capacity. When I refilled mine from empty last week, starting from empty, oil began flowing back from the filler hole well before a full litre, which is what I was expecting it to take.
GuyW

Guy my 1975 owners handbook (given to me by Nigel) says 1 3/4 pint or 1 litre.
Chris Madge

Frogeye WSM gives capacity as 1 3/4 pints or 1 litre so the same.
Bill Bretherton

Those were the figures I was going on. Including the bit that flowed back out plus residue left in the bottle I reckon it only accepted about 850cl
GuyW

Guy,
was it bone dry before refill, what about trying to turn the axle to see if it distributes more.

I've often found after even a careful rear axle refill that oil comes out rather than needs topping up even on the checks 6 and 12 months later.
Nigel Atkins

Yes Nigel, this was the first fill after rebuilding the axle so it was completely empty. I did wonder if it would take a bit more if I waited overnight for it to seep into corners. But I was checking what other's found, even though the tables say 2.3 pints / 0.99 litres. I did grease parts pretty liberally when I rebuilt it so I suppose that will displace some oil capacity, but not by 150cl. Maybe the axle isn't quite level enough as the car still looks high on its rear suspension to me.
GuyW

Ok, what I'll do:

1. get the diff out and check the crwon and pignion surfaces

2. if OK I'll give the overhaul chance, found some info here: https://www.mgexp.com/article/mg-midget-and-sprite-differential-rebuild.282

3. if not OK, stop

In the meantime I'll drive tne 4.22 (screaming througg August)
a.o. arnold

guy

If it helps I have never got a litre in mine. 850ml sounds about right. Providing the ground is reasonably level and its come out of the overflow at the rear of the diff, I think its fine. Certainly I have never had a problem.
Bob Beaumont

I think you are right Bob. I am certainly not worried about it! Just wondered if perhaps tgerecwas a variation in the hight of the filler hole on different diff cases.

Sorry, back to a.o. Arnolds' topic!
GuyW

I have only just noticed, my dif has 2 filler plugs!
GuyW

Hey? Wrong cover? No just hey?
Nigel Atkins

Guy

Austin A30/A35 and possibly others, didn't have a filler plug in the axle casing, so the filler plug was in the side of the diff.

It is therefore possible to end up with either two filler plugs, or no filler plug.
Dave O'Neill 2

Mine is definitely a 4.2 diff as I checked when I had it apart when I was hoping for a 3.9 !
GuyW

Guy, The 4.2 diff was fitted to a35's A40's Morris Minors and Spridgets. Your unit could be from any such car including a factory recon. I don't think the levels will be different whatever filler hole you use.
Bob Beaumont

Bob, did the original Sprite diffs have an oil filler as well as one in the axle back plate?

Of course having filled it, it now leaks from the drain plug so it is going to need doing again anyway.
GuyW

Its only the sprite and midget that have the filler in the axle. The others all have it in the diff as far as I can recall (minor a35 and riley 1.5).
Bob Beaumont

Afraid I'll have to contradict you Bob.

My '68 Minor Traveller has its filler in the casing, exactly the same as my '67 Sprite. I've had the Minor since 1976 so I'm pretty sure it's original.

The 4.55 diff that I have on the shelf has a filler but I've no idea which vehicle it started life on.

I also have a 3.9 on the shelf and that doesn't have a filler.

I now have oily fingers and grubby knees after double-checking them all in the garage and shed! :)
C Mee

colin

Fair enough, perhaps the later Minors were different??. Years ago I had a 1955 minor and the filler was in the diff and not the casing. A friends A30 also had it in the diff but it may have been a 4.55 ratio. I was really trying to say all the spridgets have the filler in the axle.
Bob Beaumont

So I inspected the diff, not bad I must say. Checked the pinion bearing, seemed OK.

I cleaned it up a bit and retorqued the nut and checked to get a 12 in-lbs in drag.

I think (and hope) to have it right. No new crush washer. Hard to get hold of here :-(
a.o. arnold

Mate has a MM 1000 van to which he fitted a M/major centre and found he had no filler bung
he pulled an axle and filled it through the side
William Revit

You can also fill it through the breather hole, if you remove the tube.

I did that on a Midget once, when I couldn't get the filler plug out.

It always pays to check that you can remove the filler before draining the oil ;o)
Dave O'Neill 2

This thread was discussed between 22/06/2020 and 08/08/2020

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