AMC gearbox trouble

My gearbox is very difficult to shift into & out of 3rd gear, it is the standard AMC box in a '57 Norton model 77 similar in most respects to the gearbox used through the Commandos (not a laydown, or upright box). Chain tension is correct, clutch is working properly. I removed the outer cover & moved the quadrant manually, difficult to move into & out of 3rd. Removed the inner cover,gears (as many as I could with the gearbox still connected) & shifting forks. All gears slide effortlessly on the shafts, the quadrant & cam gear go through all positions easily once the forks & gears are removed. I don't see anything out of the ordinary with the gears, bushings, dogs, etc. & cant find the smoking gun!!!!! Just wanted some input before I take off the entire primary, clutch, sprockets,chains, etc. & remove the box from the bike.

Thoughts???????????????

Skip Brolund

There are many things happening from 2nd to third and 3rd to forth. Un-dogging one and dogging another at the same time in various orders respectively.

I would say your problem is either or both worn bushes and/or worn shaft where the bushed gears have worn a ridge in the shaft. Which one is a 50/50 guess.

Perhaps if you can pinpoint which particular action effects or causes the malfunction will give you an idea on which componant might be failing.

There could also be an issue with the shift detent plunger and cam plate relationship.

Study these picture to see the function on order and get a real feel for what is going on on there.
Scroll down the see the gear cluster in each of there positions fron N to forth.

http://www.oldbritts.com/gearbox_info.html