'77 GS750 Transmission problems

[77GS750]

Maybe someone can enlighten me on a problem I am having with my ’77 GS750. The engine is stock but still running really strong. The bike had a bit too much backlash in the final drive when I bought it, clunking when powering up and backing off, but shifted ok. Now it has developed a buzzing vibration which goes up and down with engine RPM’s and the shifting is somewhat more harsh. I have changed sprockets and chain and checked the clutch bearings and all I can come up with is the transmission must be in need of rebuilding. I am not an expert on this procedure. I am guessing the gear dog sets are worn. I can rock the transmission input shaft ( drive sprocket) a good 15 degrees or so.
I guess I am wondering if it is possible to get new transmission parts and if there is someone that can maybe inform me on if I am looking at this problem correctly. I really don’t want to give up on this bike and scrap it out.
Please advise.
Thanks.

[Nessism]

Backlash in the transmission parts is normal and not related to wear for the most part. One caviot though, your rear sprocket is attached to a rubber cush hub which often develops play thus increasing lash at the rear wheel. You can try to take off the rear wheel and see how the rubber looks on the hub. Even if there is play though it's not likely to cause the vibration issue you talk about.

I'm not sure what the exact problem is with your bike but poor shifting is often related to a draging clutch. Make sure the clutch plates are not sticking together and that the plates are fully disengaging during shifting.

Good luck.

[Jackrp]

Backlash in the transmission parts is normal and not related to wear for the most part. One caviot though, your rear sprocket is attached to a rubber cush hub which often develops play thus increasing lash at the rear wheel. You can try to take off the rear wheel and see how the rubber looks on the hub. Even if there is play though it's not likely to cause the vibration issue you talk about.

I'm not sure what the exact problem is with your bike but poor shifting is often related to a draging clutch. Make sure the clutch plates are not sticking together and that the plates are fully disengaging during shifting.

Good luck.

I had the clutch center hub loosen up and cause nasty noises and poor clutch action on my 1000.Some thing to check as there is a big ol nut holding that hub on.

[77GS750]

Still looking for the problem

Thanks for the replies,
The cush rubbers are new on the rear hub. The clutch basket nut was tight and the bearings and plates look good, still need to measure them for wear. The front sprocket is new and on tight and the shaft feels smooth when it is turned like the bearings are good.
The funny thing about it all is the buzzing vibration that appeared out of no where when I got on the gas one time and ran through the gears up to 70 or so and held steady on the throttle. After a mile or so out of the blue comes the buzz and it has never left. It seams to go up and down with the engine but not in the lower crankcase or the valve train. Seams to be related to the drive.
Thanks