Clutch release bearing

Any topics pertaining to the BMC A-Series engine.

Clutch release bearing

Postby johnmcguire » Wed Apr 22, 2015 9:17 am

I have rebuilt and resurfaced the slipping clutch on my 948 and it is back in the bugeye and working fine. It appears that the clutch release bearing remains in contact with the bearing on the pressure plate even when the clutch is not "engaged" or pushed in.
There is not a return spring on the slave cyclinder to pull the piston back so the pressure plate springs push the release bearing to a neutral or touching position. However the two release bearing surfaces are still in contact although not pressed against each other. Can I assume this is the way this is supposed to be?
I understand why it is best to not sit still for long periods with the clutch pushed in as these two surfaces are then wearing on each other. But when in gear and cruising along the bearing surfaces are still rubbing on each other under a little bit of pressure exerted by the spring in the slave cyclinder.
A return spring on the clutch lever would make sense to me but evidently is not necessary.
What do you experts think?
Thanks, John
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Re: Clutch release bearing

Postby Charlie Tolman » Fri Apr 24, 2015 12:47 am


The clutch throw-out bearing on a Sprite is somewhat similar to a disk brake situation, where the design relies on a small run-out (out-of plane, or wobble) of the disk surface. With a very small residual pressure in the brake caliper piston, about 2 psi, and with the disk sometimes slightly touching the brake pad, the caliper piston is forced to retract slightly, resulting in very little contact of the disk and brake pad.

I probably would not install a return spring on the clutch arm, since this arrangement might push the piston back a considerable distance in the slave cylinder, thereby creating an extra distance for the piston, push rod, clutch arm, and throw-out bearing to travel, when depressing the clutch pedal. There might be too much "free play" in the total linkage.

Charlie T.
Charlie Tolman
Judson Supercharged
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Re: Clutch release bearing

Postby peter an5l » Fri Apr 24, 2015 2:12 pm

agrred Charlie !

and isn t there this rubber thing not only for dust protection but beeing helpfull if new, to work as a kind of very little spring helping the fork and the bearing to go free ?

( wow, hope anybody can understand my writing . )

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peter an5l
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