Potential major gearbox issues with my 1976 Honda CB750...

[lowdercaleb1108]

I just got my first ever classic bike (and first ever CB750) 2 days ago, stoked as hell and super happy with it.


However, I have encountered an issue I've been having ever since I bought the bike 2 days ago. When I shift up from 1st to 2nd while in motion, the higher my rpm, the more it... clanks... it has a very ratchet-y feel to it. It doesn't clunk into gear, it grinds a little then it engages, it's like that with every gear, downshifting is fine, it clunks and it doesn't grind going down.

I just rode it 45 minutes ago and I was testing each gear, riding the bike hard and seeing if the gears would jump out, when shifting from 3rd to 4th, it put me in neutral and it did not engage, I was being firm with the shifter. Later on, I took the bike down a long straight road and decided to wind it out a bit and under heavy load in 4th gear, it jumped out and put me in neutral, couldn't upshift or downshift into gear, would just grind like hell so I slowed down a little, then upshifted and it got into gear.

I'm not the most mechanically inclined neither am I super knowledgable about these bikes, this is my first one, but this may be an internal issue. I don't think it's the clutch, it's properly adjusted and has the right amount of slack. Yes, I changed the oil yesterday, I put Rotella T4 15w40 in it.

Is it worn gear dogs? Broken/bent shift forks? Damaged shift drum? Bad transmission bearings? I mean the bike only has 21k miles on it, can these things break that easily with this many miles on the bike? I am aware that if I need to inspect (and replace/fix the troubled parts if there are any) that I would need to take the engine out of the bike and split the case. If there is anything that is broken and needs to be replaced, where do I go about getting gearbox parts? Can't find anything on the aftermarket except for refurbished NOS parts from other CB750s.

Please help. Thank you in advance, I spent alot of money on this bike and assumed that it would mostly be in good working order, seems like that may not be the case.

 

[UK K6]

Have you checked the clutch adjustment (inside the right side cover)?

Dangerous to talk about oil....
I don't know Rotella. Is it JASO MA2 spec (which is the stuff meant to be suitable for a wet clutch)? Also, the spec for our oil is 10W40 and 20W50. I have tried both and in hot weather I think, possibly, the gear change is smoother with 20W50. The engine is slightly quieter too. But, that may all be in my head...!

 

[dirtdigger]

I saw your post on facebook, glad you came on here. Anyway, yes it could be any of the things you mentioned, worn dogs, shift forks shift drum worn bearings.....all of these could cause harder shifting and or jumping out of gear. yes engine needs to be pulled to fix any of these issues but you can flip it upside down and pull the lower case and leave all the engine intact. These dont shift light like modern bikes they need a firm shift. have seen people light foot the shifting and then pop out of gear. It does sound like yours maybe does have some worn dogs or other issue though causing the poping out of gear. Although I am not fond of your oil choice it wont cause jumping out of gear. 1 to 2 shift will always be more clunky then other gears as you are shifting through neutral. You can pull the side cover and make sure the pins on the end of the shift shaft arent loose and can inspect the shift lever linkage but thats all you can do without splitting the case. Cycle xchange is the go to for cb750 parts. If you have worn dogs then get their undercut transmission and you wont have poping out of gear issues but you still have to inspect the shift forks and the shift drum and bearings.