gearbox interchangeability?

[SeanW]

Have done a couple of 100 miles on GS since rebuild - all going well apart from has developed minor leak from gearbox output shaft in last 2 days (probably; need to get rubber boot off to check, but this seems more likley than leaking bevel box?)

also, not entirely convinced the gearbox sounds healthy when you spin the rear wheel in neutral

didn;t touch the box during rebuild - just put new oil in, so it could well have been poorly already; also the previous owner had been running it for ages with a massively shagged driveshaft - don;t suppose that would have done the gearbox output shaft much good?

had my 1979 R80/7 box rebuilt last year, so was thinking the best /cheapest bet short term might be just to stick that in the 100GS - if it's a straight swop (80 is in need of a new bottom end so isn;t going anywhere just now)

Anyone know if this is possible? Are the ratios wildly different or in the same ballpark?

 

[Voyager]

We need Rob Farmer here .

I have a feeling that a 1979 box would be for a 'heavy flywheel' bike, in which case the input shaft is different to the later ones. They can be modified but they're not a straight swap.

A full set of bearings, seals & springs is coming-in at around £250 these days. so re-furbing your existing box should be a viable option. That assumes that all the pinions, selectors & shafts are OK of course.

I've just finished one so PM me if you want me to take on another

Bob

 

[Steptoe]

Anyone know if this is possible?

No - input shafts are different as is the clutch pushrod and operating mechanism etc.

 

[Beemerboff]

Is it possible to change the complete clutch, gearbox and flywheel ?

 

[SeanW]

I've just finished one so PM me if you want me to take on another

Bob

Thanks for offer; may well take you up on that.

Woudl I be right in thinking that to replace the seal you have to take the backplate off whatever?

 

[Voyager]

Would I be right in thinking that to replace the seal you have to take the backplate off whatever?

No, the Output Shaft seal can be replaced without stripping the back off the box.

You will have to remove the speedometer drive gear (easy) and the drive flange (special tool needed) though. When replacing the drive flange, the nut has to be torqued-up to 161 ft/lbs.

Kenny was doing one on his Paralever, his experiences would be useful .

Bob.