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MG TD TF 1500 - Mark II rear axle ratio

I have a chance to pick up a Mark II differential and was wondering if it has the typical ratio which seems to be 5.125. I'm still rebuilding my TD and now would be a good time to change my high ratio for a lower ratio to make it more highway friendly before the car gets completed.

Thanks,

Mark
Mark Strang

I think the Mark II had the 4.875 like the TF.

Mark Sherman
Mark A. Sherman

If it is inexpensive, it would be a way to go...however, the 4.30 from an A or early B drops the revs more and certainly can be handled by the XPAG!
gblawson(gordon)

Hi Mark,

Because the ratio refers to the input (5.125) to the output of the axle (1.0) going to a 4.875, 4.55, or 4.3 actually RAISES the rear axle ratio, not lowers it. So the 5.125:1 is a lower ratio and the 4.3:1 is a higher ratio.

I have the 4.3:1 in my car and with my minor horsepower improvements have no problem with the raised ratio.

warmly,
dave
Dave Braun

I just disassembled a TD rear axle for rebuilding with 3.9 gears from an early MGB and found 4.55 gears installed. Don't need the 4.55 gears and still looking for the 3.9 gears. Marvin
Marvin Stuart

Marvin - unless you have really tuned that TD engine, I would be a little concerned about a 3.0 ratio in a TD - you will really have to work to climb hills with that installed.

Does anyone else have this ration installed?

I would think even a 4.1 would be questionable. My fathers with a 4.3 is a little gutless on hills and you may find that you can only climb in second.

Just a thought,

Jeff
J. W. Delk

My Mark II originally had a 4.875 ratio. I thought it was a 5.125 until I cleaned off the housing before disassembly and found 8/39 stenciled on the back. I made the change to a 4.3:1 and have been very happy with the result. I have little problem with hills because there aren't any around here. This part of Kansas is relatively flat.
John Masters

Jeff -- For a while I had a 3.9 diff in my TD. It handled it OK and we do have hills in New England. But in the end I went with a 4.3 and put the 3.9 in my TF1500. That seems a better combination. A 3.0 if there were such a thing would be almost unusable IMHO.
Cheers,

Bob
R. K. Jeffers

I have the standard 5.125 diff in my 1950 TD and I like the low gears, since I shift a lot and there are plenty of hills over here to do that.

I have been thinking for years of installing an Austin-Healey overdrive modified for a TD which I have - shown and described in issue #6 of Totally T-Type, November 2004, available on the Web with a free download. But I never find the time. :-(

Denis
DLB Denis L. Baggi

Jeff, the 3.9 equipped TD axle will be powered by a Ford V8-60 engine. I re-geared my present blown (marshall-Nordec) TD MK-II with 4.3 gears, does just fine. Marvin
Marvin Stuart

This thread was discussed between 09/05/2009 and 10/05/2009

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.