Another wild-hair thought.... will this work??..
What if I use the bike's tranny for all of the 'normal' shifting duties, but put a small, light manual car tranny 1/2 way down the driveshaft to give me reverse and 'overdrive' (using it's 5th gear)?..
The car tranny (rear wheel drive) would have no clutch/bellhousing.. it would just be a u-joint in and a u-joint out.. In my tiny brain, it seems it would work if you only ever shifted the car tranny while stopped.. For example, you'd basically leave the car tranny in 4th gear (1 to 1 forward ratio) almost all the time (remember, the 'normal' shifting duties are performed by the motorcycle's internal tranny)... ocassionally you'd shift the car tranny into reverse when needed (back up, stop, then shift it right back into 4th gear to get your 1 to 1 forward ratio back).. and if ever you knew you were going on a freeway trip, you could put the car tranny into 5th gear (overdrive) before you took off on your way.. Best idea ever, right
There is an issue trying to shift a manual car tranny without a clutch, but again- if you did all of your (car transmission) shifting at a standstill, could you not coax/force the shifter through it's travel? There's also a weight penalty, but maybe you could remove the car tranny's unused 2nd and 3rd gears for some weight savings?
If this could be made to work, maybe you could plan for your car tranny's only forward gear to be overdrive (5th gear), which would allow you to take out 2, 3 AND 4th gear (more weight savings), and maybe then use a rear differential that would have eluded you before due to gearing (i.e. a Miata IRS diff with it's 'undesirable' ratios)?? But wait, there's more! If you (ok, this is all about me..) could use that Miata diff (because I'm now in 'constant' overdrive), I could save so much weight using it (Miata Diff) instead of the Ford 7.5 diff I have now, that I could conceivably come out 'even' on my aformentioned weight penalty!?!!?
Solved the puzzle, didn't I?!?
Alright, go ahead and tell me it can't be done..
Strip me of my dreams and reason for living- I can take it...