Need clutch advice, also possibly new tranny. Best bang for buck?

[nickels767]

1980 CB750C

So, the bike makes ~15hp above stock. I don't know how, it was built before I got to it.

Here's my current issue. The "free" tranny I got with the bike clunks its way through changes, and will on rare occasion, pop out of gear. If I want it to stay, I have to kick 1-2, 2-3, and 3-2 as hard as possible. 1-2 normally takes two attempts to make it stick.

I've also got the clutch slipping above 6500 rpm.

What's my best shot here? I've seen some built racing trans online for $200-$400, and I've seen clutch packs, basically from $40-$180.

Anybody know what I should go with? I obviously can't use factory spec parts, because the bike has too much power to play nicely (and I ride 9/10ths, all the time). I didn't buy it as a commuter.

Would like to get this dealt with before I start the visual resto this winter (don't worry, I'll start a thread, probably once I begin on the trans... I'll ride the effed clutch until it drops below freezing or it decides to completely die)

[LukeM]

Working on the clutch is easier and probably cheaper than tearing into the transmission.  Get the FSM from the home page of our little forum, pull the clutch, and inspect all the plates.  Check the basket for warpage, and check the springs. It's possible there's some weak springs in the clutch pack. If you're getting 12 more horses, that's an increase of about 20% over stock.

Getting into the trans means splitting the case halves. If you're going to re-do the cosmetics on the engine over the winter, I'd hold off on the tranny work until then.

It sounds like there's an  836 kit installed, maybe.  I don't know if the trans gears from the CB900 would fit in a CB750 case. That would be an interesting and potentially beneficial upgrade if it would work.

Luke M

[nickels767]

Anybody know anything about Cycle X's race transmission for these bikes? Decent for $225?

[Truck]

I'm not sure if 900 tranny parts would work due to the 2-stage system it uses. Would be interesting to find out.  As for a high performance tranny, that sounds a bit excesive, especially if you plan on using it for a daily driver. They are not made for nice gental shift and crusing around.  I'd personally look into checking your clutch. Shiney or Tools might correct me on this, but these biks are built pretty sturdy and a 15 hp gain shouldn't be to much for the stock parts. And as far as the hp increase is that dyno proven? any engine will lose HP as it gets older. A "performace upgrade" by a PO might just bring the bike back to stock.

[nickels767]

Not certain as to the power, it has not been dyno'd. I'm 215lb, and if I'm sitting normally, I get front tire lift at 7500 in first, and it sprints through to redline in fifth without much hassle, and then slowly goes on to about 10,500 before it starts misfiring. Does that sound about right for stock? I should also note I'm down a tooth on my drive sprocket... I do too much highway mileage to be screaming along at 5000rpm all the time. Swapped that out early on.

I know a race trans'll shift harsh, so that is where I'm having issues. I ride the hell out of my bike on weekends, but it is also my daily commuter.

I know the clutch itself is toast (slips, wobbles, etc...) but my tranny, today alone, has decided that coasting down in first is against it's will, and always spits me into neutral at around 4000rpm. It will also normally kick me out of third, requiring an upshift to get back into 3rd, or a downshift which normally lands me in neutral.

I'm open to anything. Who makes a solid reman or new tranny? Hopefully something that comes prepped in such a way to be more or less an easy job.

[TOOLS1]

nickels767 wrote

Not certain as to the power, it has not been dyno'd. I'm 215lb, and if I'm sitting normally, I get front tire lift at 7500 in first, and it sprints through to redline in fifth without much hassle, and then slowly goes on to about 10,500 before it starts misfiring. Does that sound about right for stock? I should also note I'm down a tooth on my drive sprocket... I do too much highway mileage to be screaming along at 5000rpm all the time. Swapped that out early on.

I know the clutch itself is toast (slips, wobbles, etc...)

If that is all it will do, you are down 15 +/- horsepower. Dumping the clutch at 7500 RPM, that bike should flip right over, and slam your skinny butt right down into the pavement! Also, no wonder your clutch is bad!
The clutch being out like you describe can, and will cause all the shifting problems you mention. Fix the clutch before replacing the transmission. You might not need to touch it.
TOOLS

[nickels767]

Sorry bud, rolling along at 7500 is where I have lift.

I'm sure that if I could drop the clutch, that I would flip over doing 6000rpm. 4000rpm is as high as I'll normally rev it to get rolling, again, my clutch won't take any more.

So yes, if I punch it from 2000rpm in first, I get lift around 7500 rpm. If I'm tucked, I get no lift.

Let's pretend the bike is stock (because despite being told it was tuned... it doesn't feel it to me). I will spice it up later so I'd like whatever parts I throw into it to be able to handle a 25% bump in power.

[shinyribs]

There are two CB900's. On has a standard 5 speed gear box and the other is that funky hi-lo 10 speed setup.

The standard 5 speed 900 tranny and clutch will fit your 750 cases just fine. I have an '80 750 with those 900 parts in it.

As far as aftermrket clutch plates,IMO,save your money. Put a good set of springs on there and get stock replacement plates. I've been abusing(dropping the clutch at 6k+ quite regularly...aka:daily) stock plates on my '76 for a long time now with zero issues. But I am using EBC springs. <-I think they were $14 shipped to me.