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Discussion Starter · #1 ·
Hey all. I have a 1972 CB350. Just recently the transmission has started slipping while I'm driving in 5th gear. It acts as if the clutch were being pulled in and released periodically despite not actuating the clutch. I have adjusted the clutch tension to where I feel confident that when the clutch is released there is no pressure pushing the plates apart. My question then is this. What are the chances that I just change out the clutch plates? What is the possibility that the actual transmission is failing? I would rather not change out the clutch plates only to find that I am still going to need to split the cases to replace the gears and shafts. The bike only has around 15k miles on it. It's hard to imagine that the transmission is failing but then again the same goes for the clutch plates at that point. Any insight/advice on this problem would be much appreciated. Thanks so much.
 

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There is nothing wrong with your Transmission. The bike is 46 years old so my guess is clutch friction and drive plates. Also only use motorcycle oil with Jasco rating. The use of automotive oil in bikes with wet type clutches will cause them to slip. Hope this information helps. Sincerely . Jeff
 

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If you get up to speed in 4th gear and then pull in the clutch, give the engine a burst of revs and let the clutch out quickly (as if you had powershifted to 4th) and the clutch slips, then it's the clutch (or, you could just powershift from 3rd to 4th as a test). If it doesn't slip noticeably in 4th under a heavy load like that, but does what you've described when you go to 5th gear, it's possible there is wear on the 5th gear engagement dogs causing it to try to jump out of 5th under load. Clutch slip doesn't go in and out under acceleration... if the clutch is bad enough to slip in higher gears, it's a continuous slip that only finally grips when the throttle is rolled off a bit, reducing load on the clutch. Yes, oil or additives not suited for wet clutches can absolutely be a part of the problem if it really is the clutch, but your description sounds as though it could be 5th gear engagement itself
 

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Discussion Starter · #5 ·
I've put wet clutch motor oil in the engine. Maybe today I'll try accelerating hard in 4th gear and see if I can get it to slip under those conditions. If my understanding is correct that would mean that it is indeed the clutch. If it ends up being the transmission though I have to split the case to change these out, right?
 

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Yes - if it's the trans then the bottom end will have to come apart. The clutch can be replaced easily while the engine is in the frame
 

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If it's the clutch, it may also be possible the clutch springs became weak, and the plates are alright. I think you can buy harder clutch springs for most older bikes. I never did this (never actually had a clutch issue yet), but if you open it up, I suggest you first measure the springs, if they are in the right specs. If you replace the plates, I'd probably not be a bad idea to also replace the springs. It will make the lever a bit harder to squeeze, but then I think the clutch shouldn't slip on its own, even if you use synthetic oils.
 

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Top gear is where a failing clutch starts to show. This is where the most torque is required between the engine and the ground. Based on your confidence in the clutch adjust ment I would try and oil change and if that doesn't do it, pull the side cover and check the clutch. I would expect the springs to be soft. Unless it has been driven hard or the clutch allowed to slip a lot, the disks might be OK. If it was me I would just replace everything with new OEM parts if possible.
 

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Much/many "bits" in the oil and or filter, sump floor also.

Gear selection selecting properly/positively ?

Seems to be "jumping out of gear" then jumping back into gear ?

Does it only seem to do it on half or more throttle, or all/any of the time ?

Does it do it on very light throttle ?

Does it do it on the overrun ?

Is the clutch cable fouling/tight on steering lock to lock ?

Has it been "crunching" gears, difficult to get into gear etc. ?

Does it do it in any other gear ?

Check gearbox shaft end float.

Suspect gear dog problems.......check what gears/dogs involved in 5th gear, you know of cmsnl ?

Suspect jumping out of gear
 

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>98% chance it is the clutch. You do not OEM parts to fix it. Barnett makes excellent clutch components but can be pricey. EBC and others also have friction plates. No special tools needed except, possibly, a hand impact driver if the engine side case has never been removed and still has Philiips head screws.
 

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Hi Eric,
I have a CL450 that I have rebuilt, and it recently started experiencing the same issues as your bike. Did you ever find out what the true issue was? If so, how did you resolve it?
 
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