In the process of returning an MGA to the road, I experienced an unusual
problem with the hydraulic clutch. I found that after about 10-15 miles
of driving I would encounter clutch slip. It would get to the point
where gentle acceleration up a slight grade would cause slippage.
I noticed no other symptoms of oil on the clutch facing, i.e., no judder
or roughness when engaging the clutch from a standing start. This led
me to thoroughly examine the hydraulic system. Besides, I really did
NOT want to pull the engine until I was absolutely certain that the
hydraulics were functioning properly.
When I rebuilt the clutch and brake master cylinder (combined on a
pushrod MGA) I followed John Twist's advice about relieving the front
cover gasket to allow the brake m/c piston to come back just a bit more
to insure that the compensating port was not covered by the primay cup.
You simply relieve the front cover gasket to allow the piston to come
back about 1/32 in more. All the discussion about this problem centered
on the brake system and how the brakes would lock up. I'm here to tell
you that the problem can affect clutch operation, also.
I noted that if I let the car cool down completely, the slippage would
not be present until I had driven a few miles and things warmed up.
This morning, I got under that car to check out the slave cylinder.
Opened the bleeder screw on the slave and a few drops of brake fluid
dribbled out. Took the car out for a hard drive, until I experienced
slippage. Upon return to my garage, I jacked it up, crawled under and
opened the slave bleeder - to be met by a fairly strong spurt of brake
fluid. Hmmmm.
My guess was that the clutch m/c primary cup was covering the
compensating port, or at the least obstructing it significantly.
(Remember, after it cooled down, all was well.) I also guessed that
engine compartment heat was causing the clutch hydraulic fluid in the
line to expand, thereby actually activating the clutch enough to cause
slippage.
Operating on that theory, I managed to get the front cover gasket off
without too much aggravation and relieved the clutch side as well. Have
just returned from another 20 mile test drive - and this appears to have
done the trick.
Realize this is a bit wordy, but thought the MGA crowd would appreciate.
Bill
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