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MG Midget and Sprite Technical - Decent quality diff gaskets

Just changing the diff on my car and I am shocked at how thin the replacement diff gasket is, its a Moss part and its just thin paper. Does anybody do a thick more card type gasket like the one on the car now?
R Mcknight

had the same problems myself, even the holes didnt line up right, also from moss. get yourself some sheets of gasket paper and make your own. a lot cheaper as well. just bought a sheet about 48" by 18" for a fiver at car show.

regards bob.
bob taylor

Is that the brown paper gasket on the rear wheel axle assembly ...is so, that it, no mistake, it really is supposed to be that thin, hard to belive ah ?

Ive heard of brown paper bags being used, but I dont think thats a permanent solution.

Prop
Prop and the Blackhole Midget

no prop - talking about the 'pumpkin' gasket.
David Smith

I have some genuine Rover/Unipart diff gaskets and they are seriously thin and need careful stretching to get them over the studs.
Dave O'Neill2

I've found that letting it soak in some oil for an hour or so makes it actually fit. I've also just used RTV and no gasket ... worked quite well.
Trevor Jessie

John Twisting (making your own) with gasket paper, brown paper, and cereal box card all works well. Apart from petrol related fixes I always soak in oil first and they work as well or better than the real thing most times. I prefer to do this than resort to Hylomar.

;-)
Dave Squire

The gaskets have always been thin. The holes don't line up due to the material losing moisture content and shrinking between manufacture and use. I soak in water for about 5 seconds, then pad dry with a towel. That restores the moisture content without making them at all soggy, and makes them back to size. I fit dry (without any goo) and they don't leak.
Paul Walbran

They seem to be difficult to fit because of the poor alignment of the studs... and even worse if you try to take if off after a trial fit as the holes will then tear. I must admit to using blue gunge as well - that sorted it and at least that's one area that hasn't leak.

There is a similar problem with the gasket on the hubs themselves. They seem very thin too. Is that just poor quality or how they have always been? I thought the idea was that there would be sufficient squash to take up any uneveness.
Graeme Williams

The standard halfshaft gasket is thicker than the diff gasket.
Dave O'Neill2

x2 what Trevor, Paul and Dave Squire said (and John Twist): wet it first for best workability, and brown paper bag paper works very well, if one is handy with a scissor.



Graeme and Dave O'Neill switched gears now, mentioning the hub gasket (the one that Prop brought up but was quickly "shushed" for doing so).

The Bentley manual states that the hub gasket must be at least 0.010" thick, IIRC.

I have never been able to figure out why on that point. The half shaft x diff gear engagement length has plenty of allowance, and so does the overlap of the drum to the brake shoes, so those can't be the reason for it, and those are the only things that are affected by that gasket thickness. Well, that and the squish of the O ring, but squish is what O rings are really good at. Since plenty of folks have fitted their hub with no gasket at all (just liquid gasket) maybe that Bentley warning about the hub gasket minimum thickness was carried over from earlier o-ringless hubs or something.



Norm
Norm Kerr

And for my own cars I've dispensed with the hub gasket altogether. Reasoning is that modern applications rely solely on O-rings so why can A-series and banjo B-series diffs. Eliminating the gasket gives a bit more pinch on the O-ring too as Norm notes, so even better. This has been a 100% successful approach.

IIRC very early examples (pre-Spridget) didn't have the O-ring and relied solely on the gasket. That being the case I can well envisage the O-ring being viewed originally as a back-up, without the performance record we have today on O-ring seals to give confidence to eliminate the gasket altogether at the time this change was made.

However, for customers' cars I prefer to be "factory" so still fit the gaskets as well as the O-rings.
Paul Walbran

I thought that in the case of the hub gasket, the paper thickness will control the amount of "grip" imparted to the bearing outer race, to ensure that it doesn't turn in the hub. But if that is the case, it would be better to err on a gasket too thin than one too thick. So the Bentley manual quote (which I haven't read) would seem to be the wrong way round. I would expect it to quote a maximum, not a minimum paper gasket thickness.
Guy W

we are straying farther and farther off topic, away from pumpkin gaskets towards hub gaskets, but here is a sketch of the hub system, and you can see the thickness of it doesn't matter to the bearing

I made this sketch because I too was wondering about that.

orange = back plate and drum
green = axle housing
blue = half shaft (W/W shown)
red = hub bearing
purple = hub


Norm




Norm Kerr

Drifting further still then :).

What do you do about this gap (8 thou), if you don't use a gasket?

Without a gasket, the flange will deform when the wheel nuts are tightened. But maybe that doesn't actually matter, since some people have already dispensed with the gasket and had no bother.

Lawrence Slater

Ah ha, that photo helps to show where my sketch was missing a key detail. Lawrence, does the bearing sit proud of the flange (the surface with the studs sticking out) by the 0.008" that you mentioned?

Is the mating surface of the half shaft flat between where it is bolted to the outer ring, and where it mates to the bearing's outer race, or is there a step in the half shaft mating surface?

I had been trying to remember the shape inside there, and couldn't find any detail in the manuals.


BTW, is the 0.008" a measurement you made of this part or did you find it in one of the texts?

PS: that is one nasty looking bearing in that photo, it looks like someone greased it with rust.

:)

Norm

Norm Kerr

Hi Norm.

The 8 thou is the actual measurement I obtained as you can see in lower photo. I tightened the halfshaft against the hub without the paper gasket or o-ring, and that was the gap that remained.

The mating surface of the half shaft is flat. The outer race of the bearing sits just proud of the o-ring retainer. So yes, I'd assume that the bearing sits proud by circa 8 thou, as there's nothing else to hold the half shaft flange off the hub. I ran a straight edge over it and it looks about right. I should have measured that too. I took these pics for an earlier discussion, but never posted them.

The "rust" you see in the ball bearings, is congealed grease :). The rust you see on the inner bearing came from the surface of the half shaft as I inserted it. I picked up two rear hubs complete with bearings from someone for a 5 quid. He had painted and then packed them with grease and left them for 20 years. As far as I can tell they're new bearings. I'll wash them out in petrol one day, when I need one of them.




Lawrence Slater

Are you sure that is the correct bearing and it is properly seated?
Trevor Jessie

Yes and yes Trevor. If you magnify the image of the bearing, you can see the R&M lettering. :).
Lawrence Slater

Norm: on your sketch there's nothing giving a positive location to the outer race in the hubas far as i can see. Doesn't the face of the hube extension (with wires) or the dish end of the steel wheel half shaft clamp the bearing to locate it?
Graeme Williams

Graeme, you are correct, that is what was missing from my sketch, and was clarified by Lawrence's photos.

If the 0.008" is correct, then that will nicely explain the BMC manual minimum gasket thickness note for the hub.


Norm
Norm Kerr

But if the gasket is any thicker, then the outer of the bearing is not clamped and it can shuffle in the hub, ultimately wearing it out. Banjo B's suffer from this in particular as their bearing is recessed in the hub and a spacer makes up the difference ... and the spacers I've ssen are too narrow so no pinch on the bearing outer.
Paul Walbran

Paul, you had me worried for a minute. I didn't recall seeing any spacers on my B.

I've just looked at the M*ss catalogue and it says the spacer is for steel wheels only.
Dave O'Neill2

Very interesting discussion. Long long ago Growler, South wrote:
And I shall start raving about fully-sealed bearings (you know, the pre-lubed type with integral oil seals)
They're lovely. Last forever and supplement the existing oil seal- no more leaks, and no more damaged bearings from differential metal flakes.
SKF part# 6207zz
NSK part# 6207vvc-mav2


Well I bought them (the SKF ones) they are cheap abundant available and they lasted so far. I brush the hub ant the shaft flange, use the thin gasket (to prevent the shuffle), the O ring and Hylomar. It is important to compress the gasket with the oversized nut over the wheel stud (see Laurence second photo) before you turn the shaft to hub screw. There is only one. Why?

Flip

Flip Brühl

Flip,

Strictly speaking the zz suffix is for dual shielded bearings not seals. The shield will help keep contaminants out but will still allow some flow of oil. Designations vary but 2RS is a common suffix for a bearing with 2 seals.
David Billington

Dave, guilty as charged - just being a bit lazy about the ww version's difference.
Paul Walbran

Flip you asked ---
"before you turn the shaft to hub screw. There is only one. Why?" ---- I guess that's because it's the wheel nuts that do the real clamping.

Here's another pic. In my earlier pic, the nuts I used must have distorted the shaft flange a little, and reduced the gap to 8 thou, even though I didn't think I'd done them up that tight. With a straight edge though, it's clear that the outer bearing sits proud of the hub by 10 thou.

So if running without a paper gasket, when the wheel nuts are fully tightened, the flange must distort even more. Does this matter? I guess not, if people have been doing it with no ill effects.

Lawrence Slater

This thread was discussed between 01/10/2013 and 10/10/2013

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