Early/Late clutch swap question

mick71b

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I need to buy new clutch plates for my 71b, and was wondering if I can/should change to the later (78) clutch hub/basket setup for a little better operation. I already have the parts to swap, so if it's a good idea, I'll do it now and be done with it.

Thanks
 
Hey, Mick, curious as well, will be watching your thread. All I can offer is:

Be mindful of plate thicknesses, both fibres and steels.

Something I need to check on mine, the fit and squareness of the pushrod mushroom into the pressure plate. Some pics on this forum reveal strange looking surfaces in the center of the pressure plate, wondering if it affects disengagement feel...
 
Mick,

According to the parts fiche the outer basket is the same through the entire model run so if you do decide to change over to, what I am guessing you are after, the later "spring loaded" clutch all you would need to change would be the inner clutch boss and pressure plate. Hope this helps at least a little bit.
 
Thanks guys, I guess I'll just tear them both apart and see what I can do. The early plates are no longer available, so I have to get the later ones and make them work.
Any recommendation on what brand of plates I should buy or avoid?
 
****Warning this is a shameless plug****

If you are willing to be a guinea pig and do a little measuring for me I could set you up with an 8-pack clutch that uses Alto friction plates at cost. According to the math there should not be any machining needed for the Alto 8-pack clutch to fit into the early (70-73) clutches but I do not have one of those clutches to test on. The 8-pack clutch fits perfectly in the mid run clutches and the TX750 clutches with no machining and they fit the late clutches with just a little modification of the inner clutch boss. PM me if you are interested.
 
On the very early clutches the fiber plates were thicker, 3.5 mm and had rubber O-rings between them to help absorb some of the shock of engagement.
The mid years used 3 mm thick plates and left out the rubber O-rings. They added another fiber and steel plate to make up the extra space.
The later added the spring loaded plate on the hub and deleted a fiber and steel plate.
I haven't used the very early clutch so I can't say much about it. I have used the mid year and later clutches on my 750 kitted 75. The main difference in feel is the mid year clutches engage a bit harsher on initial take off but once under way you won't feel much difference.
The later clutches have the spring loaded first plate that absorbs this harsh engagement so you notice it a lot less on initial take off.
One thing I di recommend is that which ever way you go look at the steel plates, they are stamped out. This leaves a rounded edge and a sharp edge. Use a 150 or so grit sand paper to break thus sharp edge, make it match the rounded edge. This lets the plates slide easier on the hub and basket. You can check the fiber plates for the sharp edge and remove it too.
While sanding the steels sand the entire surface to remove any discoloration and rough up the surface. This will improve the grip.
I replaced the worn clutch springs with new 70 lb. Kibble White springs. The stock were around 50 lbs. new but after 35+ years I doubt they were even 45 maybe 40.
Use a well lubed cable and worm, proper adjustment and it should work well and a two finger pull, mine does.
No slippage under the extra power of the 750, easy to pull and find neutral, what more can you ask.
Leo
After a bit of trial and error I finally replaced the clutch plates with Forodo plates.
 
On the very early clutches the fiber plates were thicker, 3.5 mm and had rubber O-rings between them to help absorb some of the shock of engagement.
The mid years used 3 mm thick plates and left out the rubber O-rings.

The steels were also thicker.

Conversations I had with some Yamaha mechanics 40 years ago implied that the o-rings were to help spread the 'sticky' plates during disengagement, perhaps because of the nature of the early cork-based compositions. These o-rings were unique to the Yamaha, never saw them on other bikes. Always wondered about them and where those mechanics got their info.

... I replaced the worn clutch springs with new 70 lb. Kibble White springs. The stock were around 50 lbs. new but after 35+ years I doubt they were even 45 maybe 40.

Leo, is that the installed pressure, or the spring rate in lbs/inch, or something else?

(And why are the post font sizes unpredictable? )
 
Thanks again, guys. I'm going to go with the Ferodo plates and tear it and the '78 down and see what I have. I'll make sure to post up some pictures when I do it.

I have a stocker that doesn't get run very hard, so I'm thinkin' the 8 plate setup would be overkill for me, but surely appreciate the offer.

Mick
 
The later dampened hub is the bomb. Short of a rear wheel swap to one with a rubber mounted rear sprocket, it's the best you can do to ease the strain on your clutch hub damper springs. It doesn't matter whether you're running it hard or not. Every time you let the clutch out, it "jolts" the hub. Eventually, that breaks springs.
 
The lbs. of a spring such as clutch, valve springs is the lbs. of force the spring exerts at it's installed height. In the case of clutch springs each spring would push against the pressure plate with the 50 or 70 lbs. of force, 6 springs and you have 300 or 420 lbs. of force pushing the pressure plate. Or swap in what ever number for your springs.
To determine the psi of the pressure plate you will need to determine the area of the pressure plate gripping surface then divide the total weight of the springs by the area.
Not really important. Know the spring weights is enough. Stronger springs push harder and clamp the clutch closed harder.
I agree with 5twins on the later hub, it can soften the engagement and transmit less "jolts" to the springs.
Leo
 
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