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Old 11-07-2011, 05:33 AM   #1
MotoJ OP
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Question Airhead clutch slip in the cold

Hi,

Starting to get very cold in the mornings hereabouts. Lately my 1978 R80/7 has had some clutch slipping problems in the morning that seems to go away after the bike has warmed up (and after I start smelling clutch!).

Is this a question of trans input shaft not lubricated enough? That was done about 3000 miles ago, and it all shifted like butter up until the recent cold. New cable at that time too, which is still properly adjusted. Bike only has 15K original miles. She's been pulling a hack for a couple months now and the old girl has been complaining in various ways after having her easy way solo for so long.

What should I have in mind if I start taking this apart?

Thanks!
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Old 11-07-2011, 05:44 AM   #2
OldPete
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As an old diesel mechanic, my guess is the plate is down to the rivet heads.
Doubt the clutch disk has bonded friction material.

The guys in the hack forum might suggest a sintered material disk.

I'd check the disk before the rivets eat into the flywheel & clutch plate. Just me though.

Note: gotta lube the splines on my K75s.
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Old 11-07-2011, 06:02 AM   #3
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Probably over lubed the splines and contaminated the disk. It's a bonded disk, no rivets.
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Old 11-07-2011, 06:19 AM   #4
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Hmm...

Quote:
Originally Posted by robtg View Post
Probably over lubed the splines and contaminated the disk. It's a bonded disk, no rivets.
Why wouldn't it slip at all times, then? I was thinking too little lube and it doesn't start moving until everything warms up, like oil.
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Old 11-07-2011, 06:32 AM   #5
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Have you adjusted the clutch freeplay? If not enough, it could slip when cold and as the trans case heats you would have more clearance.
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Old 11-07-2011, 07:14 AM   #6
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Eureka!?

Quote:
Originally Posted by robtg View Post
Have you adjusted the clutch freeplay? If not enough, it could slip when cold and as the trans case heats you would have more clearance.
I will take a look at that. I suspect it's something simple.
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Old 11-07-2011, 08:12 AM   #7
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check tranny oil

front seal leak can get on clutch disc
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Old 11-07-2011, 09:22 AM   #8
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There needs to be free play in the clutch at both ends. Free play at the left lever that pulls the cable. And free play at the throw out arm on the rear of the trans that operates the clutch.

It does seem that it would slip all the time if you had over lubricated the splines.

Even with the addition of a hack it seems total mileage is too low to actually need a clutch but maybe you are driving the thing like a motorcycle instead of a chair? (just kidding)

I would check what the hack people are using for clutches. I think the stock clutch in my R90/6 is only marginal. So far I'm on the good side of that margin but I think I could burn it up pretty quick if I wanted to.

Charlie
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Old 11-07-2011, 10:47 AM   #9
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If I had a hack, even slightly hot rodded airhead, or even a completely stock one, I would run a '81 on BMW clutch. They are WAY better on a lot of different levels.

I would guess over lubed from the story. It happens all the time while doing a lube job that usually does not need to be done in the first place.
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Old 11-08-2011, 04:50 AM   #10
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Aha!

Quote:
Originally Posted by robtg View Post
Have you adjusted the clutch freeplay? If not enough, it could slip when cold and as the trans case heats you would have more clearance.

ding ding ding! And the winner is........Robtg! Gave it some more free-play at the bar and things are much improved. We'll see how long this lasts.

Thanks for all the replies- I'm going to keep my eye on the lubing methods in the future anyhow. Too much lube is not always a good thing apparently....
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Old 11-08-2011, 08:27 AM   #11
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When lubing the transmission input splines, if you lube the splines, it is important to put the grease (whatever you are using) on the input shaft male spline member only. Do not put lube in the clutch female splines.

A little bit of excess lube will then be pushed out towards the rear when the parts are put together. This excess will adhere to the front of the trans maybe or be flung out by the flange on the disk. this flange is raised so the grease here does little harm.

If grease is placed inside the female splines of the clutch it will be pushed forward when the parts are mated again. This grease will have no where to go except the friction disk when it is flung out by the spinning engine.

Only lube the male input shaft splines. Use small amount of grease. Tiny amount. Try to get to all the splines but don't glob it on.

Have you checked for free play at the throw out arm on the rear of the trans? I wouldn't harp on this but you say you adjusted the clutch lever. Well, all the work is being done by the other end of this contraption.

Charlie
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Old 11-08-2011, 09:41 AM   #12
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Of course, there are other ways of getting the same results. I lube male and female splines but I spread it thinner in the front of the clutch. I spread mine real thin with a tooth brush with shortened bristles.

I have seen so many clutches fried for letting that free play disappear. I don't understand how you can not check that free play every time you pull in the clutch. At least the first time every ride?

supershaft screwed with this post 11-08-2011 at 10:00 AM
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Old 11-08-2011, 07:21 PM   #13
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When I was regularly riding my hot-rodded '77 R100, the clutch would slip every year as cold weather began (In Vermont, that's about August 10th-in a good year). This was cured with a Luftmeister sintered-bronze clutch plate and hardened pressure plates, which are no longer available. As SuperShaft says, the '81 on clutch is a superior item, if pricey.

If you must use the '70-'80 clutch, you might consider Southland's clutch repair, or at least having the mounting bossesof the pressure ring ground to increase spring pressure.
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