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MG Midget and Sprite Technical - Differential Carrier Cracks

Hi Guys,

How common are cracks and breaks in Spridget Diff carriers?
I have fitted many Spridget and Morris 1000 (4.55 ratio) diffs to MG TCs over the past 38 years but always have difficulty finding diffs with uncracked carriers. Perhaps they often begin to crack but rarely break right through as the metal gets thicker in the middle?

I have heard of Spridget racers who don't have trouble and don't crack-test before installation. Surely I am not alone in my concern? Any comments?

I have attached a photo of a very badly cracked carrier.

Cheers,
Bob Schapel

R L Schapel

Never had a problem with any cracks either on the road or racing over the past 30 odd years. Never had any crack testing done.
Bob Beaumont




Okay Bob,

Please Explain it one more time... you had these 3 hookers in the car, you were going to dennys for a grand slam 3am breakfast... and what happened agian ???

Prop
Prop and the Blackhole Midget

I've got a Morris 4.55 and LSD in my car and no cracks. I've never heard of of that problem before.
john payne

I had it happen in a B series once, in fact it broke completely and lost drive, but most of our cars (A&B) since have had LSD's so are different.
Paul Walbran

Bob I told Lachlan that I never came across any cracked carriers. He was going to coach me in crack-testing before I sent one out to him - I guess it may have been for you? Haven't heard from him lately...
David Smith

I hadn't heard of them cracking until it was mentioned on here but I can see how they might especially if sharp edges are left on stressed edges. I noticed when I dismantled one of my final drive units where the cross pin had come out and chipped the pinion that the pinion actually had fine cracks from the base of each tooth. That edge of each tooth was razor sharp due to the way it was manufactured and would produce a good stress raiser. I guess if one was paranoid enough and had the time then all the components could be inspected and any sharp edges radiused and polished to reduce the stress raisers.
David Billington

Not something I've come across, either
Dave O'Neill 2

Have only come across that once before but it was on a B diff that had exploded

also

Sorry to hear about Bill , My thoughts are with You and your family - Very sad and way too early.

willy
William Revit

Thanks guys,

Your comments are very much appreciated. If an LSD is fitted the issue does not apply because the LSD unit would replace the bit which cracks. It sounds like it can be a problem in standard B series diffs.

I have converted over 40 diffs and so have checked out perhaps about 80. I have not taken statistics but would guess that about half are cracked. The only logical conclusion is that they do crack where the edge is rough but the cracks slow right down as they get into thicker metal and usually don't present a problem.

One friend broke at least three but he was using the 5.375 ratio from an early Morris for racing at a tight circuit. I do know that the ratios 5.375 5.125 and 4.875 have a weaker carrier. The radius is smaller, the base dimension is smaller and the metal is thinner. That might explain my friend's problem ... and he never crack tested them.

If any of you want to test a carrier, there is a simple, cheap way. Wash off the area with thinners (acetone type). Dry with tissue and spray with anything which dries as white powder. Fungal foot spray from a pharmacy will do! Oil in any crack will soak out into the powder. A tiny spray with spray penetrant on the other side is a possible addition to the method. That is what is shown in my image on my previous post ... (It can be done to a totally intact diff centre but only one or two of the four suspect areas can be done at a time.) It was an experiment. Usually I use the proper dye penetrant kit.

I always remove the crown-wheel and grind imperfections out of the area where cracks can appear. However, from your comments it seems that maybe I am being over cautious?

Thanks again for your comments.

Bob Schapel

R L Schapel

Where cracks are concerned, you can never be over cautious!
Paul Walbran

To David Smith,

Yes, Lachlan was chasing a good carrier. He wanted me to replace a cracked carrier in an otherwise good diff. I guess you will hear from him soon.

The crude form of testing described in my Nov 22nd post seems to work but I have not tried it on a carrier with a small crack. (A task for the future!) I would not rely on that alone. Proper dye penetrant testing should be done to check.

Bob Schapel
R L Schapel

This thread was discussed between 20/11/2014 and 22/11/2014

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