Are the mainshafts & layshafts on the M20 foot change Boxes from 1937-on interchangeable ?
Obviously 48 onward had the speedo drive off the layshaft but can that layshaft be used on the very earliest boxes & just ignore the fact it has the drive cut into the shaft?
Ive just read Neales gearbox info on this site & that includes some nice info & I didn't know about that selector fork change.
I've always been aware of the changes to inner & outer covers & return spring ETC but its not completely obvious to me if the late mainshaft & layshaft will fit straight into the early box, I'm fairly sure they will but would like confirmation.

Hi Fred..I know the very early boxes had a more heavily constructed selector fork shaft..not sure about the other shafts though, I've never had to work on one. I've run the speedo drive layshaft in the 38 on box without problems and the mainshafts from then on were identical...It is an interesting question though regarding the very first 36/7 boxes...I'd like to know the answer myself just for the record...Ian

email (option): ian@wright52.plus.com

Thanks Ian, I realised after I posted that I have parts books for 36 -7 -8 so I wasn't thinking it through, I can simply look at them : D

Edit, yep mainshaft 15-4260 & Layshaft 24-4394 all the way back & on other 1936 models.