Hi all..I am rebuilding an M series gearbox. The problem I am having is that there is a slight tight spot in it when the main shaft is rotated. It selects gears ok. I added more gaskets which did loosen it up but still a tight spot and now too much play in the selector arm. The Main and layshafts look straight. I am thinking perhaps re-bushing everything, might fit the issue but the bushes look ok to me. As well does anyone know where I can get hold of some new gear selector dogs as the ones in the box are worn.

Hello Bryce,

I have just finished rebuilding an M20 gearbox from most NOS part,
Including the shafts and a NOS dogs.

I found NOS dogs on eBay. they do come up from time to time.
My gearbox also came out a bit tight, mostly in one spot, (But I could turn it over manually)
And I thought I might have bent it, as I used some real force and heat to fit few of the new gears to the shaft.

I have also asked here, and the reply was that tight gears boxes eventually seizes,
But as I had no choice, I topped it with oil and installed it.
It shifts fine and all looks great.

So far I have done over 250Km on it and all is fine.
My logic is that the more it is used, the less is the probability for seizing,
So I hope it will do fine,
But basically the gearbox should be very free to turn.

Hope it helps...

Noam.

Thay's interesting, Noam.
Wonder if the box will hold after many more miles.
Let us know how you get on, oke ?

And Bryce, are you sure you have all the many rings and shims inside and on the right place ? It's very important to get the box working properly.

I must say i have rebuild gearboxes of triumph, Norton, Ariel etc, but never had any problem. BSA's need much more care and attention...

Hi Bryce, If you place one shaft at the time you can figure out if its the main- or layshaft.

You can also find tight spots when the sleeve gear is not properly rebushed.

Good luck! Michiel