Author Topic: Cb750 wont engage gears (Read 6151 times)

leesfer · « **on:** December 31, 2013, 02:53:57 PM »

1975 CB750 the motor is running for the first time and I went to see if I could ride it from one side of the garage to the other but none of the gears will engage.

If I release the clutch entirely the bike will not go anywhere, it just acts like it's in neutral even if I am in first, second, third, whatever

The clutch is new and I am pretty sure everything on that side is okay, I followed these boards for installing that and confirmed everything was good. It was doing this before I changed the clutch anyway, but I thought it was a clutch issue but I guess not

Could this be a huge tranny problem or something simple?

ekpent · « **Reply #1 on:** December 31, 2013, 03:20:19 PM »

Can you describe a little what the clutch handle pull is like. Does it pull in super easy or is there some resistance you can feel from the springs. Is there a little bit of free play on the cable by the handle. Did you replace with new parts ?

leesfer · « **Reply #2 on:** December 31, 2013, 03:44:23 PM »

The clutch has some resistance, it's not easy, but not impossible to pull. No free play at the handle

I have nothing to compare it to though, my only other bike was a modern Yamaha R6 but the CB750 clutch is stiffer than that was.

All clutch parts were new.

I should also add that when shifting through gears, 1st, 2nd, 3rd are easy but it doesn't seem to want to go past that at a stand still. Though is that just because it's not moving? Not sure, again, never had a CB750 before that... this is a learning experience for me

LesterPiglet · « **Reply #3 on:** December 31, 2013, 04:10:43 PM »

If you can engage the gears whilst stationary(engine off) by rocking the bike back and forward, then you have clutch issues. Probably adjustment by your description.

leesfer · « **Reply #4 on:** December 31, 2013, 04:33:11 PM »

Quote from: LesterPiglet on December 31, 2013, 04:10:43 PM

If you can engage the gears whilst stationary(engine off) by rocking the bike back and forward, then you have clutch issues. Probably adjustment by your description.

I will try that and report back

leesfer · « **Reply #5 on:** December 31, 2013, 05:02:00 PM »

Okay if I am rolling the bike back and forth, I cannot change gears, it's incredibly hard. But if the motor is running I can shift okay through them.

I have tried the clutch adjusting nut in a ton of different settings but still get the same effect. No matter what gear I put it in, the motor runs, BUT I can tell that the gears are KIND OF engaged as the motor runs slightly harder in the upper gears.

Sounds like it could be more of a clutch issue or something else? I feel like I am in over my head with this

HondaMan · « **Reply #6 on:** December 31, 2013, 05:24:21 PM »

Quote from: leesfer on December 31, 2013, 05:02:00 PM

Okay if I am rolling the bike back and forth, I cannot change gears, it's incredibly hard. But if the motor is running I can shift okay through them.

I have tried the clutch adjusting nut in a ton of different settings but still get the same effect. No matter what gear I put it in, the motor runs, BUT I can tell that the gears are KIND OF engaged as the motor runs slightly harder in the upper gears.

Sounds like it could be more of a clutch issue or something else? I feel like I am in over my head with this

This is interesting! (?)

A broken gear (Final Drive) could do this. It's number 14 in the image below. But, for that, I would expect you would find bits of metal in the oil pan, at least, because it would have had to shear off the splines.

An over-center clutch could also do it, which seems more likely. This can happen if, for instance, a post-1976 lifter was used in a pre-1975 clutch cover (different lengths), or if the cover used is not the right year for the lifter used, that sort of thing. This can at least be tested by turning the clutch adjust screw all the way out (CCW) until it stops, to disengage the clutch hub altogether. Then the clutch lever should be very soft to pull in, like one small finger's grunt.

Or, if the clutch is not assembled properly, like the hub is not seated into the splines so it sits against the plates, the plates will never engage. But when this happens and the little bolts are all tightened, it usually breaks the hub.

LesterPiglet · « **Reply #7 on:** December 31, 2013, 05:25:10 PM »

I meant select the gears without using the clutch.

leesfer · « **Reply #8 on:** December 31, 2013, 05:37:11 PM »

Quote from: HondaMan on December 31, 2013, 05:24:21 PM

An over-center clutch could also do it, which seems more likely. This can happen if, for instance, a post-1976 lifter was used in a pre-1975 clutch cover (different lengths), or if the cover used is not the right year for the lifter used, that sort of thing. This can at least be tested by turning the clutch adjust screw all the way out (CCW) until it stops, to disengage the clutch hub altogether. Then the clutch lever should be very soft to pull in, like one small finger's grunt.

Or, if the clutch is not assembled properly, like the hub is not seated into the splines so it sits against the plates, the plates will never engage. But when this happens and the little bolts are all tightened, it usually breaks the hub.

I am using a '72 lifter plate and I've broken two of them from not having the hub correct so I know 100% that the splines are spot-on this time around. I'll try the clutch adjust screw and see how easy it is to pull

leesfer · « **Reply #9 on:** December 31, 2013, 05:46:10 PM »

Turning the clutch adjustment screw all the way still makes the lever harder than being able to pull with one finger

On a side note, I can put the bike in any gear and still roll it around the garage with ease like it is in neutral

Maybe I messed the clutch install up

HondaMan · « **Reply #10 on:** December 31, 2013, 05:50:34 PM »

Quote from: leesfer on December 31, 2013, 05:46:10 PM

Turning the clutch adjustment screw all the way still makes the lever harder than being able to pull with one finger

On a side note, I can put the bike in any gear and still roll it around the garage with ease like it is in neutral

Maybe I messed the clutch install up

That might be my first guess. If a gear was broken, there would be some nasty noises when it was running, especially when dropped into a gear?

leesfer · « **Reply #11 on:** December 31, 2013, 05:58:05 PM »

I'll re-attempt the clutch install tomorrow and find out.

I have a complete '72 basket ready to go, this will be a direct fit for a k5 right?

HondaMan · « **Reply #12 on:** December 31, 2013, 07:57:27 PM »

Quote from: leesfer on December 31, 2013, 05:58:05 PM

I'll re-attempt the clutch install tomorrow and find out.

I have a complete '72 basket ready to go, this will be a direct fit for a k5 right?

If it is the clutch basket that has a steel ring welded to the outer ends of the "fingers", it will fit directly. Check the shape of the ends of the "fingers": if one has U-shaped ends and the other are squared-off ends, you may find that you need one more (or less) friction plate in the end. One type of basket-hub combination in the K2 era (i.e., leftover K1 clutches) had 6 friction plates, while the later ones have 7.

ekpent · « **Reply #13 on:** January 01, 2014, 09:01:40 AM »

The way you describe it it sounds like the clutch is acting like it is engaged all the time if your saying that when you "put it in gear" it still freely rolls around without using the lever.
Did you mention in an earlier post that you had these same symptoms before you replaced the clutch with new parts ? Did you or do you know if the shifting mechanism has been fiddled with or maybe the cases were split before you got it ? Have you ever officially driven the bike out on the road since you acquired it ? May be something more than just the clutch.

leesfer · « **Reply #14 on:** January 01, 2014, 10:29:24 AM »

Quote from: ekpent on January 01, 2014, 09:01:40 AM

Did you mention in an earlier post that you had these same symptoms before you replaced the clutch with new parts ? Did you or do you know if the shifting mechanism has been fiddled with or maybe the cases were split before you got it ? Have you ever officially driven the bike out on the road since you acquired it ?

I've never ridden the bike, as far as I know the case has not been split, but I have fiddled with the shifting mechanism.

Now that I think about it, I do remember cranking it in gear and it would roll before so at some point it was working

leesfer · « **Reply #15 on:** January 01, 2014, 11:12:11 AM »

OKAY! I pulled my clutch out and replaced the entire basket with the '72 one I had and now with it all back together, I can hit the starter and it lurches forward... so far so good

I am waiting on a clutch cover gasket to finish it off and test it fully

Don R · « **Reply #16 on:** January 02, 2014, 09:27:32 AM »

That's a good sign. Good luck, you're on the right track.

LesterPiglet · « **Reply #17 on:** January 02, 2014, 10:54:26 AM »

Try selecting all the gears now, engine off, without using the clutch. To make sure selection is fine. No oil or gasket needed to try this. Remember to push the bike back and forth to help the gears slip in.

leesfer · « **Reply #18 on:** January 05, 2014, 01:49:51 PM »

I finally got a gasket and put the clutch cover back and and now I have a new problem... The clutch plate/pusher thing does not touch the clutch itself so it just spins in place and when you pull the clutch lever there is too much room so it does not push the plates

Any idea what is going on?

martin99 · « **Reply #19 on:** January 05, 2014, 02:07:55 PM »

Sounds like you have exactly the opposite problem to what you started with, in that you've gone from permanently disengaged to permanently engaged. Is the clutch plate/pusher thing you're referring to the lever where the cable end is located? Try adjusting it by the book. Slacken off the cable at both ends. Screw the adjuster in (clutch end) until you feel resistance, then back it off 1/8 to 1/4 turn. Tighten the locknut. Adjust the cable (clutch end again) until you have about 3/8" to 1/2" free play at the lever, before you have to apply any pressure to pull it in. Use the adjuster at the lever for fine adjustment only. If this doesn't fix it I would guess you've done something wrong during the clutch install. Good luck!

leesfer · « **Reply #20 on:** January 05, 2014, 04:51:59 PM »

I'm a massive idiot, I had the clutch adjuster all the way out... I just needed to screw it back in to engage

bjatwood · « **Reply #21 on:** January 06, 2014, 08:25:43 AM »

Your not an idiot...you just restore stuff like most of us do the first time...wrong. When you finally get it right it makes you a subject matter expert. So, when someone else has a clutch issue, you can help them make it right!

Ellz10 · « **Reply #22 on:** June 23, 2023, 05:53:34 PM »

Quote from: LesterPiglet on January 02, 2014, 10:54:26 AM

Try selecting all the gears now, engine off, without using the clutch. To make sure selection is fine. No oil or gasket needed to try this. Remember to push the bike back and forth to help the gears slip in.

Are you saying that you should be able to shift gears without pulling the clutch?

HondaMan · « **Reply #23 on:** June 23, 2023, 07:02:22 PM »

Quote from: leesfer on January 05, 2014, 04:51:59 PM

I'm a massive idiot, I had the clutch adjuster all the way out... I just needed to screw it back in to engage

Good job!
Feels good, don't it?

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Author Topic: Cb750 wont engage gears (Read 6151 times)