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MG TD TF 1500 - 4.3:1 Crown wheel and pinion

I have been offered a second hand 4.3:1 ratio crown wheel and pinion from an MGA. I have been considering changing the diff ratio on my TF 1500 as it is 5.125:1 and not really suitable for highway motoring.
Can anyone advise me what other bits I would need if I want to make this change.
I see that Moss has a kit that they offer for the change to a 4.55:1 ratio. Is this kit suitable for a change to the 4.3:1 ratio?
TF 1500 #9901
Bill Tutty

Good day Bill. You will need beside the crown wheel and pinion, the spacer that goes between the head of the pinion and the inner bearing. Then the spacer that goes between the inner and outer pinion bearing. Both the spacers lengths will need to be ground to fit. You will also need the pinion flange to the drive shaft as the splines are different between the TF and MGA. The TF bolts that hold the crown wheel to the carrier will be the same thread. The inner pinion bearing is a different ID than the TF. I would advise that you change all bearings since you have it apart. If you have other questions be sure to ask, I've done almost 100 ring and pinion swaps.

Butch Taras
Glendale, CA. USA
R Taras

The conversion is pretty involved. Moss sells a booklet describing the procedure. You may find information buried in the archives here, or maybe "google" the subject.

The 5 speed overdrive might be a more practical modification. You can sell off the original 4 speed to recoup a good part of the swap.

On the other end of the spectrum is the MGB rear end with 3.91:1. A bit of cutting & welding to the spring brackets, and parking brake bracket modifications (for the TD anyways). That ratio is too tall for the 1250 XPAG, unless it is supercharged. The TF 1500 would be tolerable. You'll notice it feels sluggish... the "get-up-and-go" "got-up-and-left." It'll cruise 3000rpm @ 60mph - 4000rpm @ 80mph. That is way down on the power curve, only about the 40-50hp region, but I prefer that to winding the engine out on the highway. It is the equivalent of the 4.3:1 with 5 speed overdrive for final ratio.

Bill -- You may find the following two sites of help. They are from my web-site:

The are titled: Part 1 of the 4.3 differential conversion; and
Part 2 of the 4.3 differential conversion. These two will show you all of the things and references you will need to do this conversion.

Cheers -- John
John Brickell

Bill, the change over is pretty straight the saying goes, if I can do it, anyone can. The article about the Atlanta, ga. USA chapter covers the whole thing and when you are done the car still looks 100%stock, unlike a gearbox change out. Regards, Tom
tom peterson

Bill, see for some more about the conversion. Bud
Bud Krueger

Thanks guys for all of your suggestions and information. I am now happy that I can go ahead with this and do the job myself (with the help from a couple of friends). If I take up the offer of the MGA diff I can get almost all of the other bits needed locally and in the meantime I am setting about getting all the manuals and books on the subject.
I will also take the opportunity to replace the wheel bearings, and give the rear springs and shocks a full overhaul.
Thanks to Bud and John for the links to their websites and blogs. The photos were particularly helpful.
As always, the readily given super helpful advice found on this forum, is second to none.
R W Tutty


Dont know if you are aware of this, very comprehensive.

G Evans

This thread was discussed on 12/04/2013

MG TD TF 1500 index

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