Hydraulic Clutch Bleeding Made Simple

[Scott Fisher <sefisher@cisco.com>]

> 2)  I have never known a car that has a combined brake/clutch 
> fluid resovoir.

Not *modern* cars, probably, but it was common in British cars of the
Fifties and early Sixties.  The M.G. MGA and Austin-Healey Sprite, for
example, used such a setup, but they have their own mailing lists.

However, in such cars, low fluid level could introduce air into either
the brake master cylinder, the clutch master cylinder, or both.  The
common brake/clutch reservoir disappeared from BMC sports cars by about
1965.

> If I do have to replace the slave cylinder, what is the proper 
> method for bleeding?

Proper method for bleeding clutch slave cylinders is:

1.  Get a friend to help you on this.

2.  Attach a length of tubing (probably 1/4" rubber hose, clear) to the
bleed nipple on the clutch slave.  I usually try to slip a box wrench of
the appropriate size over the slave bleed nipple first, then put the
rubber hose on, in the theory that if my hands slip off the wrench,
it'll at least stay on the car.  Half the time, what happens instead is
that the wrench pulls the rubber tube off the nipple, spattering brake
fluid everywhere.  Place the free end of the rubber tubing in a suitable
receptacle, something clear but not breakable, like a plastic
water-bottle or plastic cup.

3.  Instruct your friend that when you say "Press," you want him or her
to push the clutch in all the way, and that when you say "Release," you
want him or her to let up on it.  Instruct your friend further to say
"Okay" or otherwise acknowledge on *completing* the action requested.

4.  Say "Press." 

5.  When your friend says "Okay," open the bleed nipple and let air, old
brake fluid, black schmutzy goo and other detritus go squirting out into
the tube.  Then tighten the bleed nipple.

6.  Say "Release."

7.  If you have performed steps 4, 5 and 6 more than about six or seven
times, have your friend check the clutch hydraulic reservoir and top up,
if necessary.  (There are few sounds more disheartening than the
slurping, sucking sound of a clutch master cylinder pulling in air when
it empties out.  It means you have to start again from scratch.)

8.  Return to Step 4 and continue until the brake fluid coming out of
the hose is clear, free of bubbles, and clean looking.  When that
happens, ask your friend to feel the clutch action and see how it
feels.  If he or she says it's about right, then it's time to try a
running test: put the car in neutral, start it, then depress the clutch
and try to put the car in gear.  If it goes, you're done.  If not,
return to step 2 and repeat the process.

That's the basics.  Don't overlook Step 7, that's the heartbreaker.

Note: if you haven't got a friend, the role of the person in the car can
be performed by one's wife, using her crutch (acquired because she is
recovering from a torn meniscus in her left knee) to depress the clutch
pedal.  It is traditional to reward such wives with champagne, flowers,
and compliments in email postings for decades to come.  Or if not
traditional, it's at least a damn good idea...

The same method, by the way, can be used for bleeding brakes, with the
exception that you want to start with the brake that is the farthest
from the master cylinder -- or more to the point, the brake that has the
longest distance of tubing between it and the master cylinder.  On cars
with solid rear axles, this is usually the rear brake opposite the
driver (but not always -- check the length of tubing that crosses the
top of the axle, if any, and see where the common rear brake line tees
into it).  On IRS cars, look under the car and see.  

--Scott "If I wrote the Bentley, it'd be 24,000 pages long" Fisher