I wrote some of this up for Lydia, and now it seems Ross could use it.
I think I'll post to all before everyone has a clutch failure...
----------------------------------------------------------------------------
Hydraulic Clutch System Operation
Rev. 6/15/90
Roger Garnett
|-----|
|-- --|
| |
| | <- Fluid Reservoir
| |
| |
| |
------------------ -------------------| Fluid Outlet (pipe)
Pedal Push Rod | ||----------|/ \__________
===============|| || <- Piston & __________ to slave
| ||----------|\ Rubber Seals / cylinder ->
--------------------------------------|
Clutch Master Cylinder
Normal Operation:
1) At rest, fluid is free to flow from the hole below the reservoir
into the cylinder. (or visa-versa)
2) When you step on the pedal, it moves the push rod/piston assembly
to the right. This first covers the inlet hole, and then procedes
to push fluid through the outlet pipe, to the slave. (Which in
turn pushes a piston in the slave, and moves the clutch arm.)
3) When the pedal is released, the piston returns, due to back pressure
from the clutch springs on the slave, and (in some cases) a return
spring in the master clyinder. Fluid flows back into the master
cylinder from the slave/pipe. When the piston is fully retracted,
the inlet hole is once again uncovered, and fluid may flow in to
make up for any losses. (or out, if the slave has returned farther
than it's previous position.)
Possible Master Cylinder Failures:
-Front seal fails, or pitting of cylinder wall. Fluid leaks back
towards the reservoir instead of pumping out the outlet pipe.
This will result in reduced or no slave piston movement.
The effects may vary with a borderline seal. (rebuild or replace
master cylinder)
-Air in system- master, line, or slave cylinder. Air compresses,
resulting in reduced piston movement, as above, & soft pedal.
(bleed system)
-Rear seal fails, fluid leaks out the back of the master cylinder
body, possibly onto the drivers foot. (R/R master cylinder)
-Piston doesn't return completly due to crud or rough surface. Cylinder
remains partially pressurized, and slave doesn't return, leaving
clutch in intermediate state. This may leak back slowly. (R/R master
cylinder)
-Blockage of inlet - shortage of fluid, reduced piston travel, mushy
pedal. (R/R master cyl.)
-Blockage of outlet -Hard pedal &/or fluid blows back past front seal.
(R/R master cylinder)
Clutch Slave Cylinder:
++ <- rubber boot
+---------------------------| Fluid Inlet (pipe)
Push Rod + \|-----| |
_____________________________|| | \__________ <-----
(_____________________________)| | __________ from master
to clutch + || | / cylinder
<-- arm + /|-----| |=] bleed
+---------------------------| nipple
++ ^piston w/
rubber seal (may also have a return spring)
Operation:
1) Rest.
2) Step on pedal- fluid master cylinder pressure pushes slave piston
(to the left), which pushes the push rod, and moves the clutch
arm which pushes the throw-out bearing into the pressure plate
to disengage the clutch.
3) Release pedal. Fluid pressure from master cylinder is relieved.
Spring force of clutch/clutch arm, (and piston return spring, if
fitted) pushes the slave piston back to the rest position, which
forces the fluid back into the master cylinder.
Failure modes:
-Seal fails, fluid blows past piston (and eventually begins to leak
out of the boot. Noticible as fluid loss in the master cylinder
reservior) Piston travel is reduced or eliminated. (this
can result from a torn or rotted seal, or pitted cylinder, etc.)
-Piston seizes or drags. Clutch may be engaged, disengaged, or
sluggish, depending on the position and amount of movement
of the piston. Caused by corrosion, crud, shredded seal, etc.
This may result in a hard pedal, and/or failure of the seal.
This could also destroy a weak seal in the master cylinder.
(R/R slave cylinder)
-Air in system. Reduced piston travel, clutch won't fully disengage.
(bleed system)
Comments:
-Cylinder repair kits are cheap. Even a new cylinders can be reasonable.
-Remember- USE CASTROL LMA GTX DOT4 eq. or better brake fluid, NOT DOT3 in your
British car!
-DOT5, Silicon is OK too. I'm currently running some long term tests on it.
There are some who say it may be a problem in high braking situations,
such as auto-x. It should perform much better for a low usage or stored
vehicle as it won't absorb water, and therefore should result in very
low corrosion levels. So far, so good.
-Brake systems are similar- they just have more cylinders, tubes, and other
fittings to deal with.
________
/___ _ \ Roger Garnett (garnett@tcgould.TN.CORNELL.EDU)
/| || \ \ Agricultural Economics | The All New:
| |___|| _ | 3 Warren Hall | South Lansing Centre For
| | \ | | | Cornell University | Wayward Sports Cars
\| \ |__/ / Ithaca, N.Y. 14853 | (607) 533-7735
\________/ (607) 255-2522 | SAFETY FAST!
|