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MG MGA - Gearbox 1st Pinion Shaft R&R?

The gearbox in my 59 1600 needs to be overhauled. It jumps out of second and sometimes sticks in first, have to rock the car to free it.
I have a spare MKII gearbox that's been rebuilt, acquired in a group parts purchase. I'm thinking about putting the 1600 input shaft in the MKII gearbox and putting it in the car. I can't seem to find a description of how to remove the input shaft. The shop manual calls it the 1st Pinion Shaft but I can find where removing and replacing it is discussed. Check the archives and Guru site but couldn't find it there either.
Can this be removed from the front, as it appears, or will the gearbox have to be totaly disassembled?
Any problem with using the MKII casing in the 1600? Don't recall if the tailshaft splines are the same or different.
Input is appreciated.
G T Foster

You don't need to change the input shaft. Just use the clutch disc that matches the splines. does have full tech information on overhauling a gearbox.

You cannot R&R the input shaft without doing more disassembly, as the front gear sprocket on the laygear interferes with removing the input gear. Attempting to shortcut gearbox disassembly is fraught with pitfalls, so you might spend more time that way than disassembling the whole thing.

Minimally you need to remove the front cover and layshaft to drop the laygear to the bottom of the box before the input shaft can be removed. When the input gear is removed 18 needle bearing rollers fall out. With side cover removed you might be able to fish the rollers out of the gearcase with a magnet. Then stick the rollers into the new input gear with grease for reassembly.

Then comes the near impossible stuff. Without removing the shift rods and forks (and maybe reverse gear) it would be very difficult to reach inside to reposition the laygear and two thrust washers before reinstalling the layshaft. When you finally get frustrated enough you might remove the remote shift housing, rear flange, speedo drive gear, tail housing, and withdraw the shift rods to get the forks out of the way. Then reverse gear is just one small bolt holding the shaft, giving access for your hands to reposition the laygear. That's about 90% of total disassembly. So if you want to change the input shaft, you might as well plan on disassembling the whole thing for inspection while you're at it. Otherwise, return to the first paragraph.
Barney Gaylord

If it jumps out of second, then a new bearing at the joint between the two gearbox casings is probably called for, which means a total strip down and rebuild. As Barney says, just use the MarkII box with a suitable clutch disc. I use a B clutch cover with a standard A friction plate on a 1500 box.

dominic clancy

I ran into another cause of jumping out of 2nd gear. One time I had a gearbox where the 3rd gear retaining thrust washer had come loose from the mainshaft, allowing parts from 3rd gear through 2nd gear and the 1-2 sliding hub to move axially on the shaft. It would go okay under load, but it would pop out of 2nd gear on overrun, when you let off the throttle with engine braking. The difference in thrust direction comes from the angle of the helical gear teeth.
Barney Gaylord

Use a different clutch disc? That's way too easy...:)
Thanks for the tip.
PS: It does go OK under load and jumps out when you let off.
G T Foster

This thread was discussed between 26/01/2008 and 28/01/2008

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