81 gearbox, clutch carrier fit 78 R100/7 or 77RS?

[moosehead]

Have access to good 5 speed box, clutch carrier and swingarm/drive shaft and rear drive (drum) from an 81RS that came in to me riding buddy John(boy)'s shop. Was a front end write off thanks to a deer hit (rider OK but lotsa damage to front end) but from engine back there are lotsa good items so johnboy picked it up from insurance co. after accident and towed to his shop.

My R100/7 basket case has spun clutch plate splines and instead of redoing clutch was wondering if the complete rear end (clutch carrier, gearbox, swing arm, drive shaft, and rear drive (drum)) could bolt up to either a 78R100/7 or maybe 77RS?? I like the cush drive shaft of the post 80's bikes and 5 speed boxes were nice too. Think I read somewhere re: length of input shaft on post 80 vs pre 80 bikes?

Guess one answer would be to see if it will bolt up to the /7 but before do that just wondering if you gurus have some insight first.

PS: the smucked bike had 79,000 on the clock but the tranny had been redone AT 74,000KMS according to PO!

[Garnet]

I'm not completly sure, but I think as long as you stay drum to drum, everything should swap from the swing arm back. Swapping the new clutch carrier and 5 speed for the heavy flywheel is a pretty common swap and should only need new flywheel bolts (which should be changed every time anyway.). The shifter up to 77 is different than 78 on but they are interchangable.

[mattcfish]

I'm not completly sure, but I think as long as you stay drum to drum, everything should swap from the swing arm back. Swapping the new clutch carrier and 5 speed for the heavy flywheel is a pretty common swap and should only need new flywheel bolts (which should be changed every time anyway.). The shifter up to 77 is different than 78 on but they are interchangable.

I swapped to an 83 tranny and clutch setup on my 75' R90. You need to use the post 80clutch and flywheel (carrier). The pre-81 clutch and flywheel won't work right because of the shorter input shaft and different lever travel. You also need a 9 tooth starter.
The post 80 tranny and clutch are a big improvement. Easy to pull, quicker revs, and a better pressure plate.

[moosehead]

Thanks to both for quick responses. So I guess will give it a go this winter. Its an 81 clutch carrier and gearbox so should work. I'll have to look at swap out of the starter as well going to 9 tooth. Thanks for that heads up! There was one n the junked 81 RS so can use that.

Going to do complete swap out of the rear end as well.

[SteveD]

Would it be easier to put one of your front ends on the wreck? Of course if there are questions of the frame being bent....

[Garnet]

Pretty sure the 9 tooth starter started in 77.

[moosehead]

Would it be easier to put one of your front ends on the wreck? Of course if there are questions of the frame being bent....

Took a direct front end hit with the deer. Every fairing piece cracked or destroyed along with bent front end and frame headstock bent as well. Even the down tubes to the cradle are out of whack as well. This guy was lucky when you see the results...only bruised thigh and forarm from going over the handlebars...yikes.

[Jean]

Your '77 should already have a 9-tooth starter. Mine does.
The '78 does for sure.
Did your friend GET the deer (for the freezer?).

[moosehead]

Ha ha... don't know. Think he was more pissed at writing off a lovely RS than worrying about road kill.

Can't believe he was lucky to walk away from this hit after seeing the bike. He did say he had no chance. No braking or avoidance but wham, right straight at it. He thinks that's probably why he got away with relarively minor injuries. If he had swerved or laid it down on the tight, tree lined back road, hitting the trees would have been worse for him. All he remebers is the hit and then flying over the handle bars and deer right down the middle of the road. Riding gear saved him more damage. Lucky.

Thanks for 9 tooth info. The 78/7 I checked is 9 tooth. Decided not going to do this transplant to 77RS...just leave it stock....for now.