Rear End Conversion

Rear End Conversions

All of a sudden you find yourself and your T-car on that frightening creature called an Interstate Highway. Certainly not the conditions for which the folks at Abingdon designed the TD or TF. Probably the pre-eminent expert in this area is Carl Cederstrand of the Vintage MG Club of Southern California (VMG). Let me quote from Carl's treatise on the subject of factory gear ratios:

"The factory selected ratios are eminently suitable for either racing or stump pulling. They are, however, grossly unsuitable for cross country motoring! I will categorically state that operation of any T series engine at a steady 4500 rpm (this is 64.8 mph with the original 5.125/1 rear end) amounts to little more than an exercise in engine destruction."

Carl's booklet on the subject, "Ring and Pinion Interchanges for the MG TD/TF", formerly distributed by VMG has been made available through Moss Motors. The booklet is a very comprehensive text on the subject and is exceptionally precise in the information presented. Some folks find the amount of data presented as being a bit overwhelming. Sort of like the idea that getting an education at MIT is like getting a drink of water from a firehose. Nevertheless, it's well worth reading to gain an appreciation for what is necessary for a successful conversion.

I've had the distinct pleasure of spending some time with Carl, discussing this topic, among others. He is a fantastic individual with an extremely sharp technical mind who enjoys little more than helping others. Carl describes his authoring of the booklet saying, "- the whole thing was a labor of love." To share this 'labor of love' Carl has authorized me to make copies for them if someone requests one. To save wear and tear on my printer, and trips to the post office, I've opted to provide the booklet information in Adobe pdf form here on Ttalk. Just click on RingAndPinion to open the pdf file.

Probably the most common conversion is to install the 4.3:1 ring and pinion from an MGA. This will change the road speed from about 14.4 mph/1000 rpm to about 17 mph/1000 rpm. In my case, with my 165/15 Dunlop SP-20 radials, I get 16.7 mph/1000, i.e., 60 mph is about 3600 rpm. I had my conversion performed by Rick Smith, Safety Fast Program chair of the NEMGTR. The conversion is something that a technically competent mechanic can do, but it's a bugger for a first-timer. The conversion has become quite popular to the point where a number of MG clubs have invested the time and effort to provide the service for their members.

The SouthEast MG T Register (SEMGTR) is right up there among the clubs that have done this. Don Harmer of SEMGTR has allowed me to host a copy of their write-up on the topic, where he added:

It was written up by Len Thomas of the Southeastern MG T Register.

Dick Lunney then edited it and Published it in Classic MG Magazine 
See the Credits at the end of the article.

This is a modification and simplification of one of Cederstrand's procedures.
One should have Cederstrand;s booklet in hand also to aid in understanding the procedure.
This reduces the complex measurements to simply machining Item 3, MGA Components, Pinion back washer to 0.094 in on a good surface grinder.
Thus this is the only thing that requires machining. Availability of an hydraulic press helps a lot.

The article is referred to as the "Virgin Rear End Conversion".

The article is an Adobe pdf file and can be downloaded by clicking here RearEndConversion3.
The article has also been reprinted in the UK MG Car Club's Totally T-Type, Issue #30