In a message dated 6/22/01 6:08:07 PM Eastern Daylight Time,
tomomalley@meganet.net writes:
<< 1. Is there any reason that regular hydraulic oil could not be
substituted for the DOT 3,4,5 etc., in the clutch MC of my '74 Spit?
(Please note: I am not considering trying this. Just curious.)>>
Hydraulic oil is usually thicker and it isn't compatible with the rubber used
in the slave system ( or the brake system ). Hyd oil will swell the cylinder
seals to 2x their size. Conversely brake fluid will swell rubber designed
for hyd oil, in fact, automatic transmission "fix it in a can" contains
chemicals found in brake fluid! (Never add this to a transmission if you
intend to use the car as a reliable transport. Sometimes it works but
usually not.)
<< 2. My slave cylinder contains an internal spring that acts on the
piston, always pushing out. It appears that the design intent is to
provide a self-adjusting clutch where lost motion is taken up
automatically. What, if anything, keeps the throwout bearing from
constantly touching the pressure plate release fingers under this
light spring pressure? >>
Nothing keeps the fingers from touching! This is a desirable condition that
will reduce finger and bearing wear. When the bearing in light contact with
the fingers, bearing speed tracks with engine speed. Since the force is very
light, bearing wear is minimal. Since the slave cyl has extra travel towards
the bottom of the bore, the clutch is self adjusting without fear of
overloading the bearing or causing clutch slippage.
In a system where there is a gap, the bearing must go from 0 RPM to 6000 RPM
in a split second. This causes finger wear from the bearing face slipping
before high pressure is applied and allows the bearing balls to skid on their
races as they get up to speed.
My around town car is a 82 Ford Escort that I've owned since ~ 91. It has ~
150,000 miles on the original clutch and release bearing. ( I purchased it
from a customer so I knew it's service history.) I changed the engine at
around 110,000 took the bearing apart, added some wheel bearing grease and
all was well. The clutch system on this car is a constant contact / self
adjusting cable type so the system does work.
Harold
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