The New England M.G. ‘T’ Register has a long history of providing its members with advice and technical expertise on the restoration and maintenance of our special cars. We present some of our favorite technical articles and tips here for members and visitors alike.
Makin’ it up as we go along. . . Tranny Troubles
The old girl, a ’52 MGTD, has been part of the family for thirty five years. Worn some, perhaps tired but still able to get it on with older and a lot more tired VW’s, she became the quintessential garage queen. I’d move the boxes and drag her out every five years or so, put in a new battery and off we’d chug blowing junk out the tailpipe. Vintage racing seemed light years away from this car, but with the counsel of a few friends and profit takers, she slowly emerged from the garage a changed girl. Lowered and sporting cycle fenders, we ventured to the track. It took a while, but before long we were driving as hard as my fear would allow, which really wasn’t all that fast.
The wear and tear of so many years of crashing through the gears had taken its toll and the old transmission finally said enough. Even a rebuild or two couldn’t keep first gear in while I pushed a little hard on the gas. The old timers said to replace the old TD transmission with a TC transmission and since I had access to a rebuilt one, I decided to give it a go. Little did I know the TC gearbox wasn’t just a bolt right in deal. It bolts to a TC bell housing, which will in turn bolt to the XPAG, or in my case the XPEG engine, but those bell housings are for small disc clutches and my car had a lightened Brown and Gammons flywheel with a Cortina clutch and diaphragm pressure plate.
Another difference between the TC transmission/bell housing and the TD transmission/bell housing is the centering ring on the face of the bell housing which mates to the transmission is larger on the TC than the TD. I had a spare large clutch TD bell housing, so I had a machine shop weld some material to the outside of the centering ring, then grind off the old TD ring while fabricating the larger TC size. I now could marry the bell housing to the transmission, then the entire unit to the engine.
Having that out of the way and having measured the length from the front TD engine mount to the rear TC engine/transmission mount I found the cross brace on the TD frame was right where I needed the rear mount to go. I hated to think about cutting the frame, but there was no way around removing the cross brace if I was going to move forward, ...or reverse for that matter. ;-)
Having struggled with just where to cut, I developed a notion that I wanted to be able to go back to the original configuration someday (?), so I cut the cross brace equidistant from the left and right frame rails, taking out twelve inches of the center of the cross tube. (Note, 12” is the minimum, 13” might be better, but it’s tight near the brake master cylinder.) I welded a plate to the stub ends on the frame and separately to the ends of the center section. These plates are engineered to bolt together with the cross tube in the original place, but if you swap the center tube left to right, it turns the old TD mount brackets around to what is now the front of the tube and displaces the center section of the cross tube back two and a half inches, just enough to clear the back of the TC transmission.
With that complete, I set about crafting a rear engine mount which transitioned from the TC trans to the now backwards TD engine mount on the frame cross brace.
First, the cradle which the TC trans sits in was cut out of angle iron and welded together. Then, using more angle iron, I made a bracket to attach to the 3 TD cross brace. It was then a simple job to hang the trans in place with its new cradle and tack the angle bracket from the cross brace to the cradle bracket on the transmission. As luck would have it, even though I measured twice and cut once, I was blown away that it fit together. There was still some engineering to do to allow access to the transmission rubber mount attachment bolts, but with a little time staring at the thing and the judicious use of a hole saw, I could remove and replace the bolts and snug everything up.
The TD drive shaft needs to be lengthened to the TC length plus about three quarters of an inch. In my case, I had a TC drive shaft and shoved it in even though it was a little short. I have as part of my stock, a TD differential with an MGA 4.33:1 gear set in it. Part of that conversion leaves the pinion shaft flange on the diff about three quarters of an inch forward of the original, so voila the TC shaft fits perfectly into the conversion.
One last bit of sheet metal work remained. The TD trans cover doesn’t fit on the TC trans, so I cut the top of the old sheet metal cover off just larger than the transmission and fabricated from a sheet of aluminum, a new top. I attached the new piece with rivnuts and screws for easy removal.
by Rob Squire #11911
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Disclaimer: All Tech Tips presented here are copyright of The New England M.G. ‘T’ Register. Be advised that every effort was made to verify the validity of each tip. But as in any free advice, it’s up to the user to judge the usefulness of each tip presented here.