rebuilding the gear box

I have been assembling a MK3 box, everything went smoothly until it came time to shift it on the bench. 3rd and 4th were difficult to engage and would take several attempts. 1st and 2nd were OK but a little rough. I double checked the shifter forks and shaft but couldn't find any problem. I had spares so I exchanged but still no improvement. Which leaves the camplate assy. I tried backing off the detent plunger but no change. I then ordered a new camplate though there was no visable problem with the old one. I can't see any wear on the worm tracks or the outside rim where the plunger rides. The new one came in, looking beautiful and the outside rim is now highly polished. Upon installation it clicked through all four gears up and down without a problem.
This leads to a question of how many 'boxes could be improved with a new shift camplate. I really can't see anything wrong with the old one even though I've inspected it carefully. It's $100 spent on a maybe but replacement might make it shift noticeably better.

seattle##gs said:

I have been assembling a MK3 box, everything went smoothly until it came time to shift it on the bench. 3rd and 4th were difficult to engage and would take several attempts. 1st and 2nd were OK but a little rough. The new one came in, looking beautiful and the outside rim is now highly polished. Upon installation it clicked through all four gears up and down without a problem.
This leads to a question of how many 'boxes could be improved with a new shift camplate. I really can't see anything wrong with the old one even though I've inspected it carefully. It's $100 spent on a maybe but replacement might make it shift noticeably better.

Click to expand...

I am in the midst of reassembly my gearbox after a layshaft bearing replacement. While the gearbox shifted just fine before the bearing failure I will have a look at the camplate and will probably polish the edge that engages the plunger in an attempt to improve shifting even further.

Polishing up the detent plunger piston and cleaning out the bore the plunger slides in made my old gearbox shift better. The plunger in my gearbox was not moving fast enough due to just being a crude rough part and old trapped unfiltered gearbox lube in the plunger piston bore. Not a rebuild project though. Still an original gearbox with nothing done to it but putting lip seals in the outer cover for the kick start and shift lever shafts.

If the gearbox is apart a new camplate couldn't hurt. Good tip.

Polish and deburr. It's the law.

Did you replace the cam o-ring (at the nut) or bush. I replaced mine and it wasn't completely seated which pushed the cam into the gears a little and kept the gears from easily changing. Also, the GB is meant to have counter resistance (from the wheel). Try rotating the drive gear/mainshaft counter to the sleeve gear when you work through your gears. Then there's the gearchange ratchet spring (ala pawl spring)

My 750 experience (posts 185-212)


There's also a lot of info on GB's on the site.

Good luck

I had seen norton people making a champher on the edge of the camplate track and s"smoothing" / polishing those track ............