Topic: No gears - Dead on the shoulder

[strawhouse]

So I got the bike towed home today... died on the on ramp onto the highway.  I was picking up speed and when I went to shift into 4th when all of a sudden it seemed to have gone into neutral.  I slowed down and pulled over... shifted into first and all I could hear was chipping metal and the slightest movement of the bike trying to move forward.  Every gear did this.  The more I tried the less it wanted to move.  The drivetrain made noise with the clutch engage or disengaged, it didn't matter.  It would shift into gear with ease but man it sounded noisy and mean when it went into gear.  There is no visible damage any where on the exterior of the bike.  When I pushed the bike onto the flatbed you could hear a clunking even though it was in neutral...   I know this thing is toast but what in the world happened?

78 CB750F 28,000 km's

[Garage_guy_chris]

Only thing i can think of is the final drive or the two gears from the counter shaft to the output shaft? Once you figure out whats up let me know i may have some parts to fix it. Im in the East end of Toronto and I have a seized  F motor that supposedly has low hours on the bottom end and may have some good trans parts to get you back up and going.

[scottly]

How do your chain and sprockets look?

[strawhouse]

Thanks for the offer.. I may be getting a hold of you in a couple of months.  The drive chain etc is all intact and looks fine.  As I said nothing external looks damaged at all... not even a drop of oil on the ground.  What I am going to do is start the hunt for a running motor to put in this thing and rebuild the F motor over the winter.  Need transportation!!

[MoMo]

I have been having a problem with 4th gear in the F motor that is in my  Red Rider.  I have to shift very deliberate and slow or there is a loud clunk sometimes followed by a false neutral.  Mine shifts fine until the motor gets hot and then becomes difficult.  Good luck with your rebuild...Larry

[timmangan]

Hey man,

I also have tones of parts just sitting around.

When time comes to it hit me up, i most probably have all the parts you want, not looking to make any money, parts are free if it gets you back on the road

Party on

[PeWe]

Find another engine?
CB750 complete or parted seems to be very cheap over there.

[timmangan]

Sorry mate, all of my parts are for 550's, my bad.

Good luck in the hunt.

[strawhouse]

Found out what is wrong... the final drive shaft is worn smooth.  Ripping that apart will be a winter project for sure.  Now onto looking for an engine to get me through until winter.

[madmtnmotors]

The actual shaft, or just the sprocket?

Picts!

[strawhouse]

Its the shaft...

[scottly]

Yeah, we want pictures! This is very unusual..

[MoMo]

Yeah, we want pictures! This is very unusual..

I'd like to see that too, it'd be a first...Larry

[strawhouse]

I will get a couple of pictures up later... just in the middle of doing a transplant.  Hopefully later tonight.

[strawhouse]

http://forums.sohc4.net/gallery/14135-110814182728.jpeg

[Bailgang]

Wow, the a first for me.

[70CB750]

Good enough for the hall of fame

You can find a replacement easy enough, it is the work that will be extensive.

[scottly]

Well, I figured it was sprocket related, but I never would have guessed the spline!

[MoMo]

Wow, the a first for me.

me too.  Never seen it on any bike in over 40 years, as Prokop said you're in the Hall of Fame

[ekpent]

There still might be some kind of jam up in the tranny to cause the spline to shear the ribs off like that or maybe improper fit of the sprocket. Did you ever replace that sprocket in its history ?  Anybody over in the drag race community ever see that problem before from all their power take offs ?

[scottly]

There still might be some kind of jam up in the tranny to cause the spline to shear the ribs off like that

If that were the case the rear tire would have simply skidded before the spline sheared. This is really odd...

[ekpent]

There still might be some kind of jam up in the tranny to cause the spline to shear the ribs off like that

If that were the case the rear tire would have simply skidded before the spline sheared. This is really odd...

That's true Scottly, just over thinking it I guess. Pretty strange malfunction.

[strawhouse]

Awesome... Hall of Fame!   
I was just as surprised, there was absolutely no sign of any resistance or jamming at any point riding the bike.  All of a sudden it just sounded like a bag of hammers going 60km's an hour.  As for the engine as far as I know its all original, but its 36 years old and I have only had it for 10.... so who knows what has happened during its life.  I will split the engine and get the shaft replaced but that is a winter project.  If I can remember I will get some pictures when I split it open.  As for the bike at this point.... the new engine is almost ready to go, hopefully a maiden voyage this afternoon.

[70CB750]

You can flip the engine and take off the bottom half and repair your transmission - there is a thread on it here somewhere.  No need to take off jugs if you dont want to.

[lrutt]

weld her on and ride the rest of the year, make it a winter project. what do you have to lose. you'll end up replacing the shaft and seal anyhow.

that's what I would do. The Honda XR650L has a bad habit of eating countershaft splines and there are a LOT of instances of guys just welding them on and riding until it wears out then doing the rebuild.