transmission 5th gear overdrive

[jefft]

Might be going into bottom end for a rebuild. Does it require a complete exchange of transmission gears on both shafts to utilize the 5th gear overdrive in a 77D. What else would be needed? If you had the 77D transmission laying before you and lets say an 83 transmission, how would you identify which was which? What about the shift forks? Would they need to be exchanged to? Any tips?
jefft

 

[jefft]

No responses. Maybe I asked a silly question? I have been emailing Mikes XS about the reason they developed a 5th gear overdrive for only the later model XS's only. I don't know what to make of their response. They said the "failure rate" probably wasn't high enough to make it cost effective to develop a gear for those models. I didn't know the later models had a failure problem. I thought he made the gear to provide a lower rpm at highway speeds. I just don't understand why he made it for the later models only. I would think if "failure rate" was the reason, Mikes would have developed a 5th gear for them first.
jefft

 

[littlebill31]

I know Punkskalar would probably know. I believe they are basically the same, except for the XS1 and XS2, I think.

 

[jefft]

I wonder why Mike's specifically states 78-84 models then?
jefft

 

[Shakey]

Going on the basis that Heiden Tuning in Holland supply pretty much the same stuff as Mikes, this is what Jerry has to say on his site about the 5th gear replacement:

24 Tooth 5th. Pinion Gear. Replaces 23T 5th. pinion gear (Oem Ref. #341-17151-04) Gear fits to stock location and makes fifth gear taller (higher top speed in fifth but less torque and less vibration) but ratios in lower gears remains the same so that acceleration & torque in lower 4 gears remains the same. Cases must be split to install. This is a "Race" part and carries no warranty other than for defects in materials. Fits: XS650's 1978 - 1984 Only! Note: Yamaha changed the shape of transmission gear teeth from 78 on and this is indicated by lines cut into the crest of each tooth.

Hope that helps

 

[grizld1]

What was changed was the splines, not the teeth. The 78 and forward shaft (you only need to change one) will install in earlier cases. The 78 and forward application listing might be a bit of a CYA; I've seen the late setup in a couple of original D-model trannies. I'd post VIN's if I thought there was a definite cutoff date involved, but I have no reason to believe that. You have to look.

 

[arowan]

So did anyone on here go through the trouble of changing to the OD 5th gear? I just split my cases due to a “noise” in 1st gear and a few chunks found when changing the oil.... debating on swapping 5th while it’s apart.

 

[TwoManyXS1Bs]

So did anyone on here go through the trouble of changing to the OD 5th gear?
.. debating on swapping 5th while it’s apart.

Yes, there's mucho info on the "OD 5th gear".
Shaft diameter warnings, plus cautions about missing the required undercutting in that gear's pockets.

Do a forum search on "OD 5th".
Read 'em all...

 

[MaxPete]

eeeeyyyyahhhh.....not so sure I'd do that one myself.

If Yamaha changed the gear tooth profile (and I am not at all certain they did) then meshing early gears with later ones might not lead to good transmission life.

If I wanted more speed / less revs on the highway, I would simply go to a smaller sprocket on the rear wheel and do a bit more shifting of gears.

 

[Ratranger]

The difference between the "OD" and stock isn't very much. If you want to make things stronger the 3rd and 5th gears from an xs750 swap in and have larger dogs. I would only do it with a 77+ transmission so tooth profiles will match.