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MG TD TF 1500 - 4.55/1 crown & pinion convresion

I have been trying to install a Moss (USA)4.55/1 crown & pinion conversion in my TD.

I have read the Carl Cedarstrand book many times, built the tooling reqired and actually did an MGA crown & pinion conversion succesfully, but the 4.55/1 does not seem to resemble the MGA set or the TD set, so I can't use the measurements that he sets out.

I have tried to position the pinion head based on patterns made with machinests blue, and have been able to get the car to run quietly under power,but when the car is coasting in gear, it makes a loud whining from about 55 MPH to about 40 MPH.

Has anybody out there installed one of these sets successfully, and if so, is there any advice that you could offer?

Thanks in advance

Mark Evenchick
Mark Evenchick

I held a workshop doing this exact conversion for 6 owners and have the following observations:

1) The Moss set is a curious mixture of MGA and TD. The catalog says to call about what extra parts to order. Although the flange doesn't need to be changed out, the bearings and spacers do.

2) Many of these gear sets are not lapped and matched. The machining marks are usually still visable. Also, the set we used specified a much tighter backlash than desirable. Both of these points will tend to cause a noisy rear end.

My recommendation is to make sure you have a backlash setting of at least .015". Obviously you also want the pinion head in the same relative location to tyhe crown wheel as specs call for. However, I suspect you don't know what that is, so the only solution is to make sure the wear pattern is checked with engineers bluing. There are plenty of good sites on the internet describing proper patterns.

Email me if you can't find appropriate data. I'll forward the instructions I developed for doing the conversion.

Lew Palmer
Lew Palmer

Thanks for the response.I used my TD flange, and new bearings and spacers. I originally assumed that it would set up using TD spec's. When that didn't work, I set it up using machinests blue, and ended up using spacers totaling .134" under the pinion head, and a backlash of .009".

I did notice some numbers on both gears, but couldn't make sense of them. Should they be the same if it is a matched set? Were the unmatched unlapped sets that you recieved returned to Moss? I spoke to a Moss tech help person and he said that he didn't know of anyone that had a problem with these gears. How can I tell if they are unmatched or unlapped? I didn't recieve any spec's or instructions with my gears. As a starting point, what spacers did you use under the pinion head to position it? Any other instructions that you have would be greatly appreciated.

Mark Evenchick

I used the Dale Mastell method, pg. 39 the "Cederstrand" manual. I had to use a "small base" magnetic dial indicator, as the normal size base did not sit properly on the pinion head. Was the head of the pinion marked + - or 0? I as you are not using an MGA gearset, you will have to glean from this what applies to your situation.( Third Edition of the "Cederstrand Manual") If the pionion head is not marked + or -, what is the measurement from pinion head to bearing face? If you need diagrams of proper patterns, i can try to find mine. Len
Len Fanelli

The "MGA" differential is common to other BMC cars of the era but different crown wheel and pinions were used including 4.55. These are reasonably easy to source with different ratios in the UK but probably not in the states. Advantage is the two gears are matched and can be set up according to Carl's book.

When I set mine up I used Dan's method but my magnetic base has a "V" cut into its underside. I thus sandwiched a piece of 1/8" ground plate between the base and the pinion head and found the magnet still held firm.

Jan T
Jan Targosz

I'm also in the Ottawa area and just about to start a conversion on my TF. I was planning on doing it myself, but the more I read about special tooling and equipment required and potential pitfalls, the more I think I should just farm it out to a specialist. Is it really as scary as it sounds? I haven't yet bought any of the conversion manuals, but what expense am I looking at for the special tooling and equipment?

Does anyone have any recommendation on the best manual or reference guide?


R Zatrepalek


Best book by far is the one by Carl Cederstrand as mentioned above. I bought mine from Moss (inexpensive)

To do the job properly you need to be a competent engineer. The really critical dimension is the "depth" of the pinion and this is set by a spacer between one of the pinion bearings and the head of the pinion. To set it you will need a small magnetic base and a dial gauge - ideally with a 90 deg converter. You will also need a surface plate (or piece of plate glass)and a piece of ground stock to use as a reference. Once you have done the necessary measurements you gan calculate the thickness of your spacer. I had access to a surface grinder but you could lap it with carburundum paste if you had patience.

You will also need some heavy weight tools such as a bearing puller with a couple of knife edges.

You will find further details in the archives.

Jan T
J Targosz

Thanks Jan,

I am a competent engineer (although electrical not mechanical by profession). I think I might search the archives for info and then give it a try. Hopefully the BBS team here will be able to help me out if I get stuck.


R Zatrepalek


If you have an original MGA crown & pinion set, and the flange, and the tooling as per Cedarstrand, it is a fairly straightforward procedure. The most difficult part is making up the tooling. I have the book and the tooling, and you are welcome to borrow them. e-mail me if you would like to get together.

I have installed an MGA set for a friend, and it worked out well. Where I ran into trouble, was purchasing the Moss 4.55:1 set. It is an aftermarket set of questionable quality that doesn't use the dimensions or clearances set out in the Cedarstrand book. I'm about to give it one more try using larger backlash clearances as per Lew's suggestion. If that doesn't work, I'll try to scrounge up an MGA set. Anyone out there have one to spare?
Mark Evenchick

Has anyone tried fitting the higher ratio diffs. 4.55 seems to be the norm but I think you can install the 4.22 midget diff and the early 3.9 MGB diff. Are these too high?

Someone out there has done it I would be interested to know other drivers opinions and the best solution for a TD.
Brett Cooper

At first, I had a 4.3 gear ratio set up in a TD rear axle housing. I was not happy with the performance of it with the two SU's. Just didnt seem to have any power to pull hills although it was great on a flat Interstate. So, I had a 4.55 set up but just after it was done, I bought a supercharger. This made the 4.3 acceptable for my kind of driving. The 4.55 has been laying in the basement all fresh and painted for installation but will not be used. My opinion is that a 4.55 is optimum, as indicated by the factory option, when using the two SU's but a 4.3 is the best with a supercharger. FWIW
Jim Merz

Our Club has done over 40 conversion over the past 7 - 8 years. Most have been to 4.3, 2 to 4.55, 5 to 4.1 and 1 to 3.9. All the TD owners love the 4.3, and don't have any trouble with the hills ( except the two whose engines need work, bad cam).

The 4.1 should be used on TF 1500's only.

The 3.9 ( from an early banjo MGB) the owner is pleased but he has somewhat compensated for the drastic change by his tire size and he drives only in flat country.

One of the 4.55's was with the Moss set and reqired different thickness spacers to be machined than the MGA's used. A surface grinder is most helpful here.

The 4.3 rear end is the most common MGA rear axle available in the US.
Don Harmer

This thread was discussed between 25/07/2003 and 08/08/2003

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