mike21091

The question I have is how likely is it that air in the clutch line could cause slippage?

The symptoms I'm having are clutch slippage only when above 7000rpm AND more than 3/4 throttle.

But then I noticed something odd, so here it goes..

I took off hard and once it hit 7000rpm it immediately shot up into the redzone and I shifted into 2nd. I repeated that a second time less than a minute later. Less than 30 seconds after that I took off again and it didn't slip at all that time.

Here are my thoughts.

- The clutch springs are worn.
- The clutch could be worn.
- There is air in the line and the heat of a couple hard runs made it firm again.

Sorry if I didn't explain it well enough but I'm just wondering what anyone else thinks about this? It'd be nice if it would just be a case of bleeding the line but a clutch wouldn't surprise me because of the mileage (46k) and the age (15yr).

Tweety

Start with a fresh oil change (wet clutch) and then fresh clutch fluid with a good bleeding... If that doesn't fix the problem, check the slave cylinder seals... Once you have gone through that, then it's time to suspect clutch plates and springs...

mike21091

Thanks, and the oil was changed when I got it 500 miles ago. I used Mobil-1 Racing 4T synthetic 10w40 since the previous owner included it with the bike.

Wicky

Try flushing the synthetic out and replacing with semi-synthetic as Honda recommend for the bike.

A problem with the hydraulic clutch such as a air in the system, low fluid would alter the bite point bringing it closer to the handlebar where the clutch engages /disengages not cause slippage par se. i.e. If there wasn't any fluid you wouldn't be to engage the clutch to change gear. Still best to change and bleed the system if the fluid looks dark and if you don't know when the it was last changed.

NHSH

Your explanation is detailed, no worries on that, I would suspect it's the clutch as well, but it is always a good practice to eliminate the easy and cheap stuff first, as mentioned above. That would be also an opportunity to give a fresh service to the bike, I bet the clutch fluid was not replaced in years, it's one of the most neglected items on the service list. Also, synthetic oil should not be an issue, but in some cases it's known to cause some slippage due to the Teflon additive.

8541Hawk

As for the oil, I've been running the Mobil 4T for years with no issues so that is not the problem.

Also the clutch in this bike is pretty stout.... I still have the stock plates in mine (though I did replace the springs a little while back) and it has close to 100K miles on it.

smokinjoe73

I agree that air in the line would have the opposite effect. It wouldnt "ride" the clutch like you describe, it would make you have a hard time getting it in or out of gear. (poor mechanical transfer of force due to compression of air). Plus, unlike a brake system the cluth does heat its fluid the same way.

If it winds up to be slipping (which by your account it is) you can tilt the bike on its side (jack stands or a pile of tire w/blanket) and remove the clutch cover to inspect.

In the race paddock it is common to carefully remove the plates and scuff them like you would do to resurface a brake rotor. (I use a ball hone) but you can use fine(ish) sandpaper on the steel plates. Check the friction plates like you would brake pads as really thats all they are. If they are SUPER thin, replace. (I think we share plates with the cbr900rr). If they arent scuff them too with slightly rougher paper (220) and repack the whole thing.

For sure at high milage the springs will wimpen (tech term) but you can put new ones in for just a couple $ or get barnets (stronger) but it will be a harder lever pull. OR...you can alternate barnet and stock to get desired put but new stockers should solve the issue..

At those miles you are ahead of the curve but it depends on how it was ridden.

smokinjoe73

Oh, as if that wasnt enuff.

My 2 cents is replace them since you are mucking up you hands anyway, but depends on your frugality.
92 95 Honda CBR900 Friction Clutch Plate Set 1206 | eBay

but the cbr uses a different number of plates in the pack so check it

smokinjoe73

Oh yeah surfer, thats true especially in dodgy winter condition. Doubtful, but something to consider

chemomche

8541Hawk

Also as counter intuitive as it is, I have had the same issue a long while back.

I had a air bubble in the slave cylinder and when I got hard on them throttle the clutch would slip. Bled the system and it went away.

E.Marquez

Mike your right, it makes no sense when you look at the design and theory of the system... But your real life experience and others that have observed the same thing support the recommendation of bleeding the clutch system (or better, dissembling the master and slave, cleaning, back together and then bleeding) to ensure no air is in the system causing slippage.

Wolverine

IMO stick with the M1 4T, best shifting feel.

And I'll +1 or +3 bleeding the clutch. Make sure you don't let the res run low(out), it's pretty easy to do.

mike21091

Thanks for the input, I'll be bleeding the clutch soon. On a side note I just installed my MCCT's today and the bike is much quieter.

Old Yeller

late to the conversation, but for what it's worth, I had your problem under hard excel. I replaced the springs with HD ones and problem went away. my clutch plates were fine.

CrankenFine

Had the 'Hawk out today for only the second time since Thanksgiving after performing repairs from Turkey Day low-side crash. I had the same experience the OP had. It never had this problem before. I wonder what he ever found in his case?

Bleeding the clutch is due anyway since the fluid is dark and I think I'll inspect the slave cylinder for gunk.

The bike only has 10K on the clock and only had 4K when I bought it so I am doubting the clutch itself. I am running ordinary Castrol GTX 10-40 for oil and it's nowhere near due for a change.

8541Hawk

Open up the slave cylinder and clean it.

Then bleed the system well and I would bet the issues go away

E.Marquez

+1000

It has fixed every SH I've worked on that had this issue but one,, and it needed a MC repair.

CrankenFine

Thanks for the quick replies. Attention deficit disorder nothwithstanding, I'll report results.

matt365

Looks like I'm getting the same clutch slippage problems.

in 3rd or 4th, at around 6,000 rpm, it jumps under hard acceleration.

I bled the clutch MC, cleaned the gunk out of the slave, and its still doing it. Inspecting the clutch is next.

Should I get a new gasket, does it have a tendency to come apart when the clutch cover is pulled?

jmathern

A new gasket is required if you are pulling the right crank-case cover. There are two spots that use "Sealant" so it is very likely that it will not make it out in one piece for you.

I'm a newb, but have pulled mine twice. lol
~Jon

CrankenFine

Finally remembered to post my resolution.

I did bleed the clutch hydraulic system since the fluid in the reservoir was very dark. BUT - I also dumped the engine oil and filter and switched to a motorcycle specific oil. Problem of slipping under hard acceleration is gone.

Since I did not disassemble or rebuild the slave cylinder, I suspect it was the automotive motor oil I had used previously that was causing the problem in my case.

SIRR1

One way to tell if your clutch is fried is to simply smell the motor oil.

Take a sniff from a freshly opened bottle of motor or gear oil, it should have a sweet and clean aroma to it.

Now remove the filler cap on clutch cover and take a good sniff of the underside of the filler cap.

You will know instantly if there is a problem because fried fiber clutch plates have an odor that really stinks and smells nothing like gear oil and it can't be mistaken for anything else!

Another smell or odor coming from used motor oil would be a mild gasoline smell to it from normal operation.

This comes from years of experience but the first thing I do after removing the oil filler cap is to smell the motor oil and to look for signs of water or coolant in the motor oil.

Hope this helps!

SIRR1