G50 gearbox mainshaft spline extensions - can they be done

[Iciclehead]

Gentlemen, some of you may recall that I am in the process of installing a 6 speed G50 transmission into my early 1989 Carrera (I had a thread going on about it a while back), all of which has gone fairly well up to this weekend's mockup.

To make a long story short, all is good except the splined section on the gearbox mainshaft is about 7 or 8 mm too short to allow the clutch disc to ride in the correct location.

I have two options....one I can trim down the splined section on the clutch disc from its current 33 mm depth to about 25 mm or I can disassemble the transmission again and machine the splines (they are involute splines), reharden the mainshaft and reassemble.

Advantages of modifying the clutch disc is that it is simple, reversible and ought to work although that would leave about a 1:1 shaft diameter to spline length relationship which is about the minimum for this application. Risk there is that I end up stripping the splines on the mainshaft or disc over time and make a real mess of it.

Advantages of modifying the mainshaft is that I could do so generously (extend the splines by 12 or 13 mm easily, gives me room to breath as it were, plus it retains all the strength theoretically. Disadvantages are cost (disassemble the transmission) and I am not sure whether anyone can reliably cut new splines and reharden the shaft to the correct hardness without making a pretzel out of it or, perish the thought, make it less tough and eventually end up destroying the shaft and gearbox in the process.

Any insight you lot might have would be greatly appreciated as well as any machine shops with the skills and experience to do this that you could recommend would also be of great value.

Dennis

[Iciclehead]

Just an update....

Finally got a hold of my machine shop guy, they can in fact extend the splines further down the mainshaft, but I need to remove it from the transmission. Looks like that is what I will end up doing.

They suggested rehardening was neither needed nor prudent....

Dennis