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MG MG Y Type - Diff ratio change

I have read the info on the Y web site about the diff ratio change. What I'm asking is if there are any direct replacement ring and pinion that fit the Y diff? Also if none is available what is the avability of a stock ratio ring and pinion for replacement. The ring gear is showing a lot of wear. I don't really want to have to set up the diff on the lathe and re-lap the gears together, messy and takes forever.

Butch
R Taras

Hi Butch,
I do not know if there are any Morris Minor diffs available in USA. Or if you would be interested in fitting a non-standard (Morris) diff to your Y-Type.

However, in Australia, several people have fitted a Morris minor diff to a Y-Type. They have been fitted to TCs for many years and the conversion is fairly simple, but a Y-Type banjo is smaller than a TC banjo, so more machining is needed to fit one to a Y-Type.

The ratios available are 5.375, 5.125, 4.875, 4.555, 4.222 3.9 and 3.727. They are hypoid. I fitted a 4.555 from a Morris Minor 1000 to my brother's Y-Tourer nearly 20 years ago.

The spider gears are interchangeable so the original axles can be used. 1/8" has to be machined off the gasket face and new holes drilled to fit the "studs" (and old holes filled). For a Y-Type, the Morris aluminium housing has to be machined back a lot (to a smaller radius) so it fits in the Banjo but it can be done.

If interested contact me at bobschapel@optusnet.com.au and I can send you more details of how to do it.

Cheers,
Bob Schapel
Bob Schapel

I agree with Bob. I had to get my YT (same as YA) rear axle housing modified to take a MM cone and 4.55 ratio diff. The standard YA setup can't fit the MM CWP set. Cost me a bit but was worth it in the long run. Copping this up front cost gave me the flexibility to try various diff ratios that aren't available with a standard YA rear axle. I finally settled on 4.22 with a hybrid of Sprigit parts.

As Bob says, the spider gears are interchangeable. But in hindsight, I should have made the change to course spline gears to give a greater & stronger choice of half-shafts, the YA half shafts being notoriously weak. Shaft breakages at the spline are the Achilles Heal of the YA/YT. I now have specially machined race-grade steel half shafts that should see me out, but if I'd changed to course spline shafts that may not have been necessary.

If you're rebuilding your diff, it's also worth researching what a Quaife diff centre might do for you. I wish I had.
R Ades

Hi Butch and R.
I believe fine splines are generally stronger than course splines. 10 splines are better than six, but 24 splines (or similar) are better still. Of course good axle material, and being new, is a good long term investment.

HOWEVER! I believe there is a process which everyone should do when they have a diff apart.

Especially if you want to stick to original 6 splines, I believe they can be made more resistant to breakage by tapering and rounding off the sun-wheel splines. If you look at the axle in the image, you can see how the very hard, sharp sun-wheel splines have cut into the axle splines. That means there is a fatigue/stress point there, which is where a crack will start. The sun-wheel splines are very hard and sharp edged (second image). I always grind them off to a slight taper and smooth that off with a small "Dremel" tool so they don't cut in so badly.
I don't know how much it helps but it must help a bit.
Bob Schapel





Bob Schapel

Hi When I fitted a 4.55 diff I machined the face back the 1/8 inch as already spoken about but I also opened the diameter to take a standard minor diff housing in the future.. The thrust washers also need to be removed to fit the gears from the Y to the minor diff housing..
Bob Wood

Just for interest, this picture shows what happened to the standard spline half-shafts I bought from Octagon Club in 2010 at some expense. I subsequently had race-grade steel shafts machined for less than it cost me to land the Octagon shafts in Australia.
I must also admit that our YT does club competition with a stage 3 tuned XPAG.
But, the standard shaft and splines are the weakest part of the standard YA/YT. So, if re-engineering your diff, removing this weakness gives peace of mind.

R Ades

This thread was discussed between 26/09/2025 and 18/10/2025

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