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MG Midget and Sprite Technical - Diff Bevel Gears

I had a slight drip from the diff pinion seal. Try as I might I couldn't shift the flange nut in situ and have had to remove the diff from the car. Even then, with a 4 ft length of angle iron bolted to the flange and a 5 ft length of pipe over the longest bar in my socket set it was still a struggle. The diff was nice and quiet but there is some backlash in the bevel gears. I am inclined to leave everthing as is, apart from a new seal, but remember in a Wheeler Dealers Edd fitted new thrust washers to the bevels in a MG B diff without removing the crown wheel. It looks to me as though on a midget the dowel that secures the bevel gear shaft can only be knocked out after the crown wheel has been dismantled. If this is the case I am certainly leaving as is but perhaps someone can advise?


Jan T
J Targosz

I replaced the cross pin and the two bevel gear 'olive' spacers on mine. No need at all to disturb the crown wheel and pinion. On mine the aim was, as yours, to reduce the backlash. It was at the road wheel rim, about 2 &1/2" down to around 1 /2"
GuyW

Hi Guy,

How did you manage to remove the shaft between two of the gears. In my diff the shaft appears to be locked with a roll pin. To knock this out I would have to remove the crown wheel and then drift the pin out.

Cheers

Jan
J Targosz

Well I remember drifting the roll pin out. And replacing with a new one on reassembly. Without it on the bench in front of me I can't say more. Except I don't recall it being any sort of a problem!

I certainly didn't disturb the crown wheel or it's bearings.
GuyW

It’s not actually a roll pin, it’s a solid pin. I’m pretty sure the crownwheel doesn’t need to be removed.

I’ll see if I’ve got a diff in the garage.
Dave O'Neill 2

I just looked at the 4.22 diff carrier on my bench and the pin is inside the inner diameter of the CW and just next to the edge of a tab washer. IIRC some people use 2 spring pins one inside the other as I think at one time the pins weren't available and were somewhat soft anyway, I had one fail which resulted in a terminally damaged pinion.
David Billington

I can confirm that the crownwheel doesn’t need to come off, but at least one bearing cap does, as you can’t access the pin directly - photo 1.

I think it would be possible to remove the pin with the other cap still in place, but you would struggle to refit it. Photo 2.

It only takes two minutes to remove the caps and lift the diff carrier out. You just need to make sure the caps go back on the same way they came off. You will normally find some numbers stamped on adjacent halves, so you shouldn’t be able to mix them up.







Dave O'Neill 2

It's a long while though my memory was that I didn't disturb anything. It was a 3.9 different if that is relevant. But now mentioned, I do recall doing the 2 roll pin trick that David mentions.
GuyW

Thanks for the responses. I have a couple more queries. What level of backlash is acceptable in the bevels. Are thicker thrust available or do I have to make up shim packs.

Cheers

Jan T
J Targosz

Jan,

Moss Europe list 5 thicknesses of the sun gear thrust washer 0.035", 0.040", 0.042", 0.046", and 0.048". Item 19 in their rear axle listing.
David Billington

Jan
If you're going to reduce the clearance, thicker sun gear washers is the go---Don't shim them,it's a moving part under load, the shims will get eaten up and go through everything
willy
William Revit

Jan, I've just been reading the WSM, which is what I followed pre internet days. And although not quite explicit the implication is that the bearing cap does need to be removed. As Dave said. So my faulty memory. Sorry!
GuyW

This thread was discussed between 16/05/2024 and 19/05/2024

MG Midget and Sprite Technical index

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