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MG TD TF 1500 - Transmission / Rear Conversion?

There's no way I could keep up with the wife in her 72 B without blowing something apart. I'm caught between the transmission and final drive conversion. A 5 speed full syncro transmission sure would make life easier, especially in heavy traffic, but the rear conversion would keep the cars appearance the same as original. I want the car to drive and enjoy safely and not be a traffic hazard. Modifying the final drive should not be a problem, if I chose to do it myself, as I've built racing rears when I was younger, so that knowledge is there buried somewhere, but it still doesn't give me a 5 speed fully synchronized transmission. How tough would it be to convert an early MGB transmission with OD to fit? Starter position? New trans cover? Shifter position? I'm kinda caught between a rock and a hard place on this one. PJ
P S Jennings

Your comment

...but the rear conversion would keep the cars appearance the same as original.

For all intents and purposes, so does the 5 speed conversion. I put in the Ford Sierra 5 speed (from Hi-Gear),and aside from the engine being about a half inch more forward, there is absolutely no other visible difference unless one climbs under the car. The shifter is in the same place.

Unless you are a purist, I highly recommend the conversion. It's definitely added to the drivability of the car.
Phil Atrill

Phil, This car has too many issues to take to concourse condition without spending more money on it than it's worth. I can't believe that the numbers are all correct, when so many other things were wrong. Believe it or not, I've only found 8 original bolts in the car! It'll look nice and very close to original, but I want it as a driver, not a trailer queen. So, again my thoughts are to make it more road worthy. PJ
P S Jennings

pj, your car to do with what you want. in regard to keeping up with the wife's B and roadworthiness, it is still going to have a single circuit, four wheel drum brake system. tell her you'll catch her at the stops as you sail by. regards, tp
tom peterson

I converted my TD with a 4.3 rear axle ratio and added a Datsun 210 5 speed all synchro gearbox. From the cockpit side, it's hard to tell anything about the mod. I can keep those huge truck radiators out of my rear view mirror without beating up the engine.

Jim Merz

P Jennings

Over 70 members of the Southeastern MG T Register have done the rear axle conversions to 4.3, 4.1 & 3.9 to 1 ratios.
The 4.3 give the same final speed in the top gear as the Ford Sierra gear box in 4th. All are very happy with the ability to drive at expressway speeds at under 4000 RPM.

An important issue is the engine condition, tune your engine to at least stage 2 tuning.

On my TF 1500 (Stage 3 tuned, 4.1/1 rear) has measured 75 HP at 5000 RPM, and I can keep up with most MGB's (not V8's) and out run them in the mountains since I weigh almost 1000 lbs less.

The rear end conversion costs much less the the Hi-Gear Kit, especially if you do it ourself. Put the extra money into porting and polishing the engine (stage 2 or 3 tuning) and you will come out way ahead.

email me and I will send you the SEMGTR's simplified conversion proceedures

The MGB tranny with overdrive would require major machining (recutting the splines) and is much bigger than the T or Ford tranny requiring major modifications to fit and mount
Don Harmer TF8986

I did the 4.3 conversion some years ago. My TD engine is basically stock and it does very well. At 60 mph, I am doing about 3600 rpms. Mountains are a bit of a challenge, but you need to downshift a little more agressively to make up for it. And, 1st is actually useable!
Steven Tobias

I did the 4.3:1 conversion, but kept the gearbox. I've driven several five speeds, and some of them almost feel like the original gearbox, right down to the 'slow synchros' ;) But in the end, I like the originality of the location of the engine and the 'proper' gearbox.

A lot of people don't realize that the very long stroke and relatively longer connecting rod means that the proverbial piston speed limit of 2500 ft/min is a non-issue on the XPAG. I routinely cruise between 4000 and 4800 RPM (66 to 80 mph with my tires, or about 16.6 miles per 1000 rpm) and at 5000 rpm the engine is loafing at 2950 fpm of piston travel.

The real limiting factor is wind buffet and noise due to the flat plate characteristics of the drag coefficient of our vehicles.

warmly,
dave
Dave Braun

I have the 4:1 conversion in my car and I run highway speeds all the time and almost never go over 4500 RPM's and no problems. I think for a cost difference is the 1000's the rear end conversion is the way to go. As for the stopping power, I also converted to MGA disc brakes in the front and they are great. Some have done the B brake conversion and like that also.

Tom Maine (TD8105)

I agree with my friend Dave. The engine really isn't working as hard as one might think, although, I felt that I was putting some serious stress on my mains! And it is a very free-revving little motor. I routinely run it out to 4500 rpms. Because of this, I never felt the need for a 5 speed. Even though my car is the furthest thing from a showcar, I've always wanted to keep with the origional spirit of the car. I love that it is almost impossible to tell from the outside that the rear is converted. Actually, the pinion shaft is of a larger diameter, but I don't remember if that is visible outside.
I also derive a great deal of pleasure knowing that I can keep the car running and reliable for reasonable cost. $2500 or more for a non-origional transmission wouldn't sit well with me!
Steven Tobias

Don't know how to thank you guys for all your input. So I'll just say, Thanks, with a lot of meaning. PJ
P S Jennings

This thread was discussed on 27/07/2010

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