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MG MGA - Replacement Transmission

I currently have a bastardized Datsun 280z 5-speed in my '62 roadster that was installed by the previous owner. It is not the "Rivergate" conversion, he did it years before that was available. The clutch pedal needs SO MUCH PRESSURE to shift between gears you practically need to stand on the pedal while shifting...sort of like pedaling a bike up a steep hill.

I recently replaced the clutch and the hydraulics are just as stiff as before. Seriously considering:

1) changing to a Ford Fiesta 5-speed
2) changing to an early MGB overdrive
3) reverting to the original A gearbox

I loved the overdrive in my old MGB but know how problematic they can be, curious as to how much to install/modify one. I suspect the Fiesta conversion is the most costly? An other advice appreciated...
Jim Paul

Jim, considering the cost of the options other than reverting to the original 4 speed, I'd suggest just checking out the rivergate kit for the Datsun transmission. One of my fellow club members here in KC recently did this conversion and loves it, no problems with the clutch. Perhaps fitting their clutch parts would solve your problem for not too much money and few hassles.
Bill Young

Jim, check the piston diameter on the Datsun slave cylinder if it is smaller than the stock mga cylinder this may well be the reason for the high pedal pressure. It is also possible someone put it a very heavily sprung pressure plate. To put an mgb overdrive in requires many modifications including changes to the transmission tunnel sheet metal shape.
John H

The original MGA master cyl has a diameter of .750 in and the slave diameter is 1.25 in. The area of the surface of the master is .4418 square in. The area of the slave is 1.227 square inches. That difference creates a mechanical advantage of 2.78 times. I believe that the Datsun slave is 3/4 in (.750) What that means is that assuming that the clutches take the same pressure to move it is 2.78 times harder to push the clutch in. I had the same problem when I used a Mazda RX-7 engine,trans,clutch and slave cyl in my 58 MGA. To fix the problem I made a piece to replace the piece that that connects the clutch push rod to the clutch pedal arm. The piece connected the pushrod to the pedal lower on the pedal arm (closer to the pivot point of the pedal arm). I could take a picture or send you a drawing if it would help. No major work was needed to get an acceptable pedal. Just a few minutes on a Bridgeport. E-mail me offline and I'll give you my # to call.
Randy
PS I know that the length and pivot point of both release arms should also be included in the formula to be totaly accurate. but what the hay ?
R J Brown

Bad news if you have a 3/4" bore master cylinder in your MGA. -- MGA properly uses a 7/8" bore master cylinder. The 3/4" bore unit was used in the 1098cc midget. If installed in the MGA, the 3/4" bore master cylinder results in abnormally long pedal travel, having to bury the clutch pedal in the carpet to get full release of the clutch, and having to double pump the brakes.
Barney Gaylord

I measured one in a box of old part that came with one of my MGA's. I' guess i won't use it in the future, thanks. I also forgot to leave my e-mail for Jim.
R J Brown

Let me know when you want to test drive my car to see how it feels. It has the Ford Serria.
JEFF BECKER

This thread was discussed between 31/08/2005 and 01/09/2005

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This thread is from the archive. The Live MG MGA BBS is active now.