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MG MGA - Gearbox inspection

I'm about to assemble gearbox to rebuilt motor. I really don't want to do a complete strip down of the box, unless I have to, or unless it is easier than it looks after reading the WSM. What are the simple checks I can do, looking in the inspection holes, etc? BTW, I have never driven this car, so no experience of noises etc. It has sat unused for about 25 years. The speedo has 58000 miles. I had to helicoil one of the clutch cylinder holes, but otherwise it seems in good condition from outside.
Art Pearse

Art-
I used to do lots of these, sometimes several a week. They always need a 2nd synchro ring, but what kills them is layshaft and bearing wear. If layshaft and bearings are changed soon enough, you get a lot more miles out of it - after that it all goes bad quick! 58,000 is about the maximum limit for shaft and bearing replacement without also replacing nearly every other piece in the box. With the trans blocked vertically upright, bell housing end up, Layshaft can be checked by removing the front cover and pulling the shaft straight up. !!!DO NOT tilt or turn the box while the shaft is out!!! If you do that, thrust washers will fall down inside and you get to take it all apart. Not that it really matters much, since the chances of finding a good layshaft on a box that hasn't been rebuilt in recent mileage is next to nil, zero, ain't happening. If the shaft is bad, the bearings are too, so that's a take apart. If the shaft is good, thank all the Gods and make many offerings of appreciation. Be sure that the flat on the layshaft is oriented correctly with respect to the front cover, or you will have the mother of all oil leaks, and probably a broken cover to boot.

FRM
FR Millmore

I would tear down enough to do a good inspection, and to replace all of the gaskets and seals. You wouldn't want to end up with oil leaks from the transmission and have to pull the engine again to fix the leaks.


Ed Bell

Far a 5-page detail on inspection and rebuild of the MGA gearbox, see here:
http://mgaguru.com/mgtech/gearbox/gt203a.htm
It is not as tough as it may first seem. No special tools required, and anyone can do it if you pay attention to details. There is additional information in the same vicinity:
http://mgaguru.com/mgtech/gearbox/gt1.htm
Barney Gaylord

A superb write up from Barney - follow it!
I would add as follows.

On page GT-203c:

Extract the mainshaft assembly out the back of the case. There is a thick plate ring mount around the ball bearing which should come out with the assembly. This ring carries an anti-rotation dowel pin which engages the rear housing and must be properly aligned during later reassembly.
***ADD: Use a punch or small chisel to accurately mark the relationship of bearing carrier to case - it helps a lot on reassembly. ***
The bearing carrier will likely also be a snug fit in the case and may need encouragement, but at least the mainshaft assembly comes out in tact with no loose parts, almost.

***At least when they hadn't been apart a million times, the rear carrier was tight enough that there was no way you were going to "tap it into alignment" as mentioned later in the reassembly discussion. If you insisted on trying, you destroyed the alignment dowel, and it still wouldn't go.***

FRM
FR Millmore

Thanks for the info guys. I guess that's one more on the task list.
Art Pearse

Hi Art. I just finished rebuilding the tranny on my 1500 roadster, just before the paint job. Your layshaft and bearings, and probably other bits WILL be worn! I would definitely pull the layshaft. Any visible or feelable wear is grounds for a new layshaft and bearings. Second gear synchro WILL also be worn and should be replaced also. Ditto for the seals, gaskets, clutch release bearing, and the clutch disc if necessary. Best of luck, Glenn
Glenn Hedrich

This thread was discussed between 02/10/2009 and 09/10/2009

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