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 CB400SF sticky clutch - ideas?
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alexibrow
Settled In Member

United Kingdom
64 Posts

Posted - 20/03/2008 :  21:40:08  Show Profile
I thought all my troubles were over - had the clutch replaced recently, fresh oil went back in as well as a full pattern clutch from Wemoto. The old thrust bearing went back in as it was as good as new.

Ever since then, when started from cold (ie left overnight or in the staff car park during the day) it lurches forwards when poking it into 1st gear for the first time (and yes I pull the clutch lever in!).

It's got worse now, to the extent that the engine now stalls when 1st is engaged. When I leave it in 1st gear with the clutch lever pulled in and press the starter button, it tries to drive the bike forward even with the front brake full on for a good few turns of the motor before it frees off and the engine starts. After that it's fine until I leave it to get cold again.

I ride it 4 days a week, a 50 mile round trip with plenty of gear changes and stops and starts, so it's getting plenty of use. There does seem to be a very slight vibration that I can feel through the whole bike as the clutch engages as well.

My mechanic says he's had it happen occasionally with pattern clutches, but has never worked out why it does this. Sometimes the problem seems to sort itself out and sometimes not. His R1 does the same thing!

He's taking the bike back in next week to check it over, but in the meantime has anyone on the forum come across the problem, and if so what causes it?

TIA.

Alex.

It's not karma, its bikema.

TektroG
Senior Member

United Kingdom
1009 Posts

Posted - 21/03/2008 :  19:27:09  Show Profile
I take it the clutch cable is correctly adjusted?

I've got 4 words for you sonny: ...
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alexibrow
Settled In Member

United Kingdom
64 Posts

Posted - 23/03/2008 :  21:18:39  Show Profile
It is as far as I can tell, TektroG. How could it be the adjustment though? it works perfectly once it's freed off.

It's not karma, its bikema.
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TektroG
Senior Member

United Kingdom
1009 Posts

Posted - 23/03/2008 :  22:02:53  Show Profile
Unlikely I know seeing as its only first. However the simplest things...

Just sounded as if the clutch wasn't engaging even if the lever was pulled in, which if the biting point was way off could happen.

I've got 4 words for you sonny: ...
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alexibrow
Settled In Member

United Kingdom
64 Posts

Posted - 25/03/2008 :  20:26:24  Show Profile
Ah, I see your logic. No, it's definitely not that. Once it's unstuck, I can engage 1st when stationary and it's fine, just a slight jump but hardly noticable really.

Any other ideas? I'm guessing that the new friction plates are all loaded up with nice new sticky oil, and the new clutch springs squeeze the oil out of the friction plates leaving a vacuum behind sucking the plates together. Pulling in the clutch lever in isn't enough to free off the stuck-together plates.

I tried rocking it in gear this morning with the clutch in, but couldn't free it. However, when I started it in 1st with the clutch in, it freed off much more easily. I managed to repeat my little experiment before I left work as well, so at least I know what to do now!

It's not karma, its bikema.
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gothy
Settled In Member

United Kingdom
52 Posts

Posted - 26/03/2008 :  16:55:54  Show Profile  Visit gothy's Homepage
u did use bike oil didnt you?

Honda CB400SF 1995.
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alexibrow
Settled In Member

United Kingdom
64 Posts

Posted - 29/03/2008 :  22:59:50  Show Profile
quote:
u did use bike oil didnt you?

Ah, but of course!

My diagnosis appears to be correct. The non-genuine clutch has stronger springs, which when the bike's parked up squeeze the oil from the clutch plates and the vacuum left behind is strong enough to hold the plates together when the clutch lever is pulled in.

My new solution is to cable tie the clutch lever to the handlebar grip when the bike's parked so that the clutch plates stay apart. Pain in the arse though, eh?!

Has no-one else come across this problem before then?

It's not karma, its bikema.
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BUGIE
Regular Member

Malta
505 Posts

Posted - 30/03/2008 :  03:37:50  Show Profile
might be speaking sh1t here but how about shortening the clutch cable so when you pull the lever in you can exert more force on the plates to seperate them?

.....Or try changing the springs
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alexibrow
Settled In Member

United Kingdom
64 Posts

Posted - 30/03/2008 :  20:41:54  Show Profile
BUGIE - I don't think adjusting the cable will make any difference. Unless I have this completely wrong, and I'm fairly sure I don't, the only time that force is exerted on the plates is when the clutch lever is released and the springs force all the plates together. When you pull the lever in, it simply releases the spring pressure on the plates, but doesn't physically separate them.

Changing the springs might help, but to be honest I'm going to wait to see if the situation improves with use. Perhaps when the clutch beds in properly (which I guess will take longer than with a car due to the oil cooling and lubricating everything) the friction surfaces will glaze/harden and absorb less oil, and contribute less to the suction.

I'll keep you posted and let you know how it pans out.

Thanks for the suggestion guys.

Al.

It's not karma, its bikema.
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