Topic: CB750 Clutch Slipping Need Help

[chewbacca5000]

The clutch on my 1976 CB750 slips really bad and the RPM shoot right up when I hit the throttle hard at highway cursing speed 70+ MPH. 
I am planning on fixing it tomorrow so if anyone knows what could be causing this it would be greatly appreciated.

[Magpie]

What oil are you using? If it says "Energy Conserving" on the bottle, it may cause the clutch to slip. Have you used any oil additives? Or, friction plates in the clutch worn to the backing? Cliff.

[chewbacca5000]

No slippery oil.  Not sure what the friction plates look like.  Will find out tomorrow. Can you describe what a good friction plate should look like.

[Magpie]

Your manual will tell you minimum thickness of what the friction should be. The picture is of my K0 clutch with plates that are in spec. Hope this helps. Cliff.

[HondaMan]

Good friction plates will have a porous look to the cork, without scratches or chunks. The plates should measure no less than 0.138" thick, with 0.141" being normal. There should not be any uneven, shiny marks on the faces of the pressure plates or steel plates.

There are a number of oils and additives that can make the wet clutch slip. One of the biggest ones: STP Oil Treatment. Also, some high-detergent motor oils like the relatively new Castrol "No Sludge Buildup" formulations, among others. Use of a motrcycle oil like the Castrol 4T is best, but there are others: you want a low-detergent oil. The 750 should use 20w40 or 20w50 oils unless it is deep winter cold: then a 10w50 is easier to start. 10w40 oils lead to rapid clutch and cam wear in these engines.

Hint: if you have my book, check the Clutch section in the Inspection or the Reassembly chapter for pictures of good plates and also worn parts.

[chewbacca5000]

Thanks Magpie and Hondaman,

The pictures help and Hondaman your description of the pressure plates really clears things up.  So if the pressure / friction plates are not porous looking and appear to be shinny or glazed then they will need replacing?

[Patrick]

From what I have seen - and I am not the guru that Hondaman is - but that if you are using the right oil, most of the time clutch slip is caused by one of two problems. Either your clutch cable is getting sticky or your clutch springs are losing their tensile strength. Try this: disconnect the clutch cable at the bottom end; move it with the lever or just tug on the wire. Does it move freely? If it is binding at all it can be preventing your clutch from properly engaging. If that is OK, pull your clutch cover and remove the star plate and the springs (you do not have to remove the clutch basket, so no heavy lifting necessary). Measure the length of the springs and compare them to the spec. If they are shorter than spec then they could be worn out. Even if they are not shorter than spec they may have lost their springiness. I always replace the springs before I go messing with clutch plates - especially back when I didn't know what a clutch plate looked like.

If both of those are fine, then look at the friction plates. FWIW, I have never run into a friction plate out of spec. I've replaced many of them, but mainly because they were old and dried out and in danger (or actuality) of disintergrating and messing up my oil pump screen.

But again, Hondaman has seen of lot more friction plates up close and personal than I have.

Good luck. You will fix it. It is not that hard.

Patrick

[chewbacca5000]

Thanks Guys! I will do a followup post tomorrow.  Think I got enough to go on for now.

[Big Jay]

http://cbrzone.com/clutches.html

Check out our extra plate clutch. You will not be able to mslip it.

[dave500]

umm?how about trying a proper clutch adjustment first,i dont think this has been suggested yet?

[chewbacca5000]

Dave,

I would try adjustment, but the engine is already on the workbench.  You see I got stuck in 1st gear over the summer and thought something was wrong with the fork ears.  Little did I know it was just the shifting mechanism that was binding up on me.  I will have payed for a semester of quality education at the school of hard knocks by the time this job is over.  O well I don't care it's my day off and my project for today.  Will let you guys know how I make out.

Much Thanks!

[Rigid]

If the clutch is slipping, and the adjustment correct, looking at the plates won't bring them back.  The slipping is all the proof you need to buy new plates.

[josephus]

mine used to slip when passing and hitting the gas heres how i fixed mine. make some shims to go under the four clutch springs make sure to shim equally. i know the clutch will get stiffer to use but i am sure honda  changed the spring stiffness.and make sure that you do have the right steel plates if it was bought from someone ive found some have a double steel plate riveted together and others that didnt have one just single steel plates. 

[Bowswell]

http://www.salocal.com/sohc/tech/clutch/cth1.htm

[chewbacca5000]

Ok it looks like the slipping problem has been going on for some time before I got the bike as the PO put in what appears to be Heavy Duty Springs.  Honda Springs are a min of 30.5.
1. 35.50 mm
2. 35.19 mm
3. 35.06 mm
35.07 mm

Friction disc are as follows:
1. .135
2. .139
3. .136
4. .138
5. .135
6. .140
7. .124

So I guess it is time to get some new plates. Does anyone know if these will work for my 1976 k engine.

Honda CB750 Clutch Friction Plate SOHC #1 OEM Ref. #22201-300-000
http://www.ebay.com/itm/Honda-CB750-Clutch-Friction-Plate-SOHC-1-OEM-Ref-22201-300-000-/190605515638?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item2c60f95b76

Thanks for all the help.

[HondaMan]

Ok it looks like the slipping problem has been going on for some time before I got the bike as the PO put in what appears to be Heavy Duty Springs.  Honda Springs are a min of 30.5.
1. 35.50 mm
2. 35.19 mm
3. 35.06 mm
35.07 mm

Friction disc are as follows:
1. .135
2. .139
3. .136
4. .138
5. .135
6. .140
7. .124

So I guess it is time to get some new plates. Does anyone know if these will work for my 1976 k engine.

Honda CB750 Clutch Friction Plate SOHC #1 OEM Ref. #22201-300-000
http://www.ebay.com/itm/Honda-CB750-Clutch-Friction-Plate-SOHC-1-OEM-Ref-22201-300-000-/190605515638?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item2c60f95b76

Thanks for all the help.

Yep, those work fine. They are coming via Thailand, have used 2 sets of them so far.

Those springs: it sounds like they are F0/F1 springs. You may wish to switch back to "K" springs for a smoother clutch engagement, lest it be sudden with those new plates.

Don't forget to at least drop those plates in a coffee can (or something) of oil to completely coat them. If you start out dry, they will destruct in just a few miles.

[chewbacca5000]

Thanks!  Do you know why I need 1 different friction plate with the swirl pattern on the 76?  Looks the same as other k clutches what is different about the 76 clutch.  Also, the basket had some sludge which is the consistency of heavy grease kinda sticky like glue would that have affected the clutch operation causing slips?  Thanks Again!  Looks like I better treat myself to your book for Christmas.

[lucky]

No slippery oil.  Not sure what the friction plates look like.  Will find out tomorrow. Can you describe what a good friction plate should look like.

You must measure the thickness of the friction plates.
Remember tolerance stack up issues. If each friction plate is-.002 and you multiply that times 7 plates then you have a .014 deficiency.
Replace the springs. Put in new friction plates.
If you keep driving it with a slipping clutch the metal plates can get hot,turn blue and get warped. Then you will have to buy new metal plates too.

It also does not hurt to check the thickness of the 30 year old metal plates. Even if they are flat.

Check the metal plates by putting them on a flat surface.  Like a glass plate, or machined surface of a drill press etc.,.

[lucky]

umm?how about trying a proper clutch adjustment first,i dont think this has been suggested yet?

You can NOT adjust a clutch.
You can only adjust when the clutch engages.

[chewbacca5000]

Thanks Lucky!

I put all the steels on a piece of glass and one or two was a little off, but no where near the service limit of .012" listed in the factory manual.  I will order more and start with the stock springs, and if I am unhappy I will switch to the Heavy Duty springs.  I really want my rear tire to hookup and not slip at cursing speeds.  I see what you are saying with the cumulative deficit of .014. 

From everything I am reading clutches are about having enough material.  People try to compensate for lack of material with Heavy Duty springs or spacers under the stock springs, but their is no substitute for having enough meat on the friction disc.

Thanks!

[Patrick]

At what speed do you start cursing? I usually get happier as the velocity increases.....

[chewbacca5000]

Yeah don't we all!  To answer your question around 65 or so I notice the slipping.  Worn disk just a matter of getting some new ones then the chore of putting the engine back in.  Thinking of waiting till March or April for that one.  Winter is time for me to fix the 4 broken engines in my basement. 1 down 3 to go!

[Don R]

Maybe you can not adjust the clutch but an improperly adjusted lifter or cable will cause a good clutch to slip. It happened to me. I posted here and no one asked if I adjusted the clutch lifter. Until I was on a trip, nearly stranded, a little light bulb lit up over my head and I tried it. It's been fine since.
 Good luck and trust your instincts.

[Retro Rocket]

umm?how about trying a proper clutch adjustment first,i dont think this has been suggested yet?

You can NOT adjust a clutch.
You can only adjust when the clutch engages.

I am absolutely sure that Dave knows that.....

[HondaMan]

Thanks!  Do you know why I need 1 different friction plate with the swirl pattern on the 76?  Looks the same as other k clutches what is different about the 76 clutch.  Also, the basket had some sludge which is the consistency of heavy grease kinda sticky like glue would that have affected the clutch operation causing slips?  Thanks Again!  Looks like I better treat myself to your book for Christmas.

Actually, you don't, unless the 2nd metal plate from the back of the stack is one of those double-steel-with-leaf-spring-between plates. This will be an extra thick plate. Some were changed out to be the Gold wing backing plate instead, to reduce clutch rattle: most of the time you are better off with using 7 cork and 6 steel plates instead.

Honda made the top friction plate into the slanted-cork plate for the F0 engines in 1976. Some of the later K6 bikes got these as the earlier clutch parts began running out: i.e., the K6 is sort of a morphed K5-F0 inside. The slanted plate is there to reduce the solid lockup in the lower gears because the F0 and later tranny had a taller 1st gear, so it needed a bit of slip to make Honda's warranty department happier. This top plate wears out QUICK in these later clutches, then causing the others to wear as well. I never reinstall the slanted-cork plates, myself, but rely on the intelligence of the rider to be intelligent about his bike. The 1st and 2nd gear dogs on the F0 and later bikes wear out more quickly than the earlier trannies because of this steep ratio: this is what Honda engineers were trying to work around by slipping the clutch pack a little longer if the clutch was dropped too hard. The down side is that the clutches also wear out sooner on the later bikes. Typically, in the K0-K5 bikes the clutch is good for more than 80k miles unless flogged or improper oils are used: in the later bikes they seldom make it past 25k miles in any case.