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 is now available through Moss Motors (Part # 212-350, $14.95 + s/h). 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 heartily recommend it.
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 an Adobe pdf file and can be downloaded by clicking here RearEndConversion3.
More on the subject later --- Bud
email to:Bud@Ttalk.info