Topic: Need help with CB750K2 Transmission trouble after rebuild

[FridgeRaider]

I have run into an issue that I can't figure out after closing the cases and installing the shifter mechanism on a '72 CB750K. I'm hoping that someone with more experience with these transmissions can help me understand what would cause the following. When I go to try to shift through the gears, it only wants to do half shifts. It feels like the gears only mesh up in certain spots once I rotate the final drive shaft (front sprocket) by hand.

This is the sequence of the events happening: shift from 1st to 2nd -> half shift up -> shift back to 2nd -> spin final drive shaft a bit -> shift to 3rd -> shift down to 2nd -> now I can't shift back down to first. Sometimes I have to do this to shift up and down through each gear, sometimes I can shift a couple of gears before it will half shift again.   

Another interesting part is if I try to shift from neutral to 1st it will sometimes half shift. It acts like it is still in neutral until I spin the final drive shaft a couple of rotations and I can actually feel the gear engage the clutch shaft (I dont know the technical term) and then I can actually shift it fully into 1st gear.

Half shift to 1st:


1st (sorry for blurry pic, you get the idea):


I tried loosening the neutral indicator thinking it might be to tight and pinning the shift drum but no change. Let me know your thoughts or if more information is needed from me.

[itsahonda4]

You will never get an accurate analysis of the shifting while trying to do all that by spinning the shaft. Can you put the chain on and have someone spin the rear wheel while you try everything. But to my mind from your pics everything appears OK. My 71 wouldnt shift preoperly from 1st thru neutral to second and it took me a couple of goes with different springs on the shifter drum assembly to get it right......

[FridgeRaider]

You will never get an accurate analysis of the shifting while trying to do all that by spinning the shaft. Can you put the chain on and have someone spin the rear wheel while you try everything. But to my mind from your pics everything appears OK. My 71 wouldnt shift preoperly from 1st thru neutral to second and it took me a couple of goes with different springs on the shifter drum assembly to get it right......

I can get it to shift through all 5 gears with manipulation, just not smooth up and down. Its out of the frame and still needs the top end put back on. Here's some pics of it right before I put them together, let me know if something looks out of place.

[754]

Part of the reason it cant shift good, is you have to support shaft behind shifter arm so that it moves properly..
 Did you try maknge the oil jets for your topend...going to need about2 bux worth of aluminum, and a some small drills.

[PeWe]

Shift thru all gears is possible when moving the outgoing axis with front sprocket.
No clutch in will not make the trans to rotate either.

I assembled my engine with bottom down and all axes in. I helped gear shifting by move the clutch hub. photos
When I assembled top case, the outgoing axis hang in the chain oiler plate fastened on top case.

If you know everything sits correct it must be OK. Normal to not get all gears in that easy without moving the trans axes.

[FridgeRaider]

Did you try maknge the oil jets for your topend...going to need about2 bux worth of aluminum, and a some small drills.

That's a big step for me to make my own. Bill Benton thinks he might have a pair from an old head, just depends if he can get them out without issue.

If you know everything sits correct it must be OK. Normal to not get all gears in that easy without moving the trans axes.

I believe everything sits ok, but I have no previous experience to base it on. I'll proceed with the rebuild and see once i get it back in the frame and possibly running.