In a message dated 8/12/99 7:59:52 PM SA Eastern Standard Time,
danray@bluegrass.net writes:
> This is the brake M/C, not the clutch. There must be air getting in
> somewhere...constant air bubbles using the suction method, not the pedal
> pump method.
There will always be air bubbles using the suction method. The reason for
this is that the bleed screw seals on a conical surface at the end of the
screw. When you open the bleeder and apply suction to the bleed nipple air
is drawn down past the threads and in with the fluid that is being pulled out
from the caliper. I have tried suction bleeders when I was working in a shop
and considered them to be just slightly less than useless. (IMHO)
> I've tried that method too and got better results, but air
> seems to get in after, leading me to believe there's a leak along the
> line/caliper/bleed valve route. And no, I haven't touched the calipers at
> all and they grab fine with the "double-pump" of the pedal to build
> pressure-
I am a firm believer in the pump it up and hold it method (described below)
However there is one area that could induce air back into the system under
the correct conditions. If your caliper pistons are pitted, when the car is
driven and the pads push back the pistons into the caliper some air could be
introduced. For this to happen several conditions would have to met I think.
First, the pistons would have to pitted, secondly the rotors would have to
have some runout to them that causes the pistons to be pushed back past the
normal running clearance supplied by the caliper seals reforming to their
normal shape. come to think of it if you have too much runout in the rotors
the rotors would cause the pistons to retract and it would require excessive
pedal travel (double pump) to get the pads back out in contact with the
rotor. Question, when you come to a stop, and let off on the brakes for a
few seconds without moving, and then step on the pedal again does it take a
double pump to reapply the brakes, or do the brakes feel normal until the car
drives again?
If the answer is that they feel normal until driven, check your wheel
bearings, they may be toast.
> so that would seem that the caliper rings are ok. Of course, I've
> learned that on a long drive, double-pedalling eventually builds heat and
> pressure to lock up the brakes! (duh!)
?? Where did you get this? The only way for the brakes to lock as you
describe is if the master cylinder does not return to the released position
(it has a spring) and block the bypass port. The danger here is not locked
brakes, but rather an emergency on the road and no time to double pump (ask
me how I know this)
> Guess I'll try the soapy water air-finding trick...This will be tantamount
> to the "divining rod" method of finding water, I'm sure.
I have no clue how you could find a leak that is pulling air into the system
by putting soapy water on the outside. (unless of course you get a very small
gerbil with SCUBA gear and put him inside the brake system and you apply the
soapy water to the outside :-)
Before you blow your brains out try to bleed the system my way.
Get an assistant.
Have assistant sit in drivers seat.
Make sure master is full
have assistant pump up pedal unit good and hard and hold foot on it.
Start with the fittings at the master cylinder. Loosen one fitting slightly
and allow some fluid to escape (put a shop towel under the fitting) do not
let assistant take foot off brake. Retighten before assistant's foot hits
floor.
Repeat two or three times until you are sure there is no air at master.
Repeat with other master cylinder fitting. If there is air in the master the
fluid will make a sound as it comes out. (listen to your car, this is a big
clue.) Many times air caught in the master will NOT bleed down to the
calipers, but can be bleed from the fittings at master.
Now go to each wheel in turn have assistant pump up bakes and hold it and
then loosen bleed screw and allow some fluid to escape.
Don't let the master go dry!
Do all four wheels this way
pedal should be high and hard, if there has been some improvement but still
not perfect, repeat.
Don't forget out of adjustment rear shoes will cause excessive travel in
pedal also. (pull e-brake on, if pedal travel is normal now rears are out of
adjustment.)
I learned this system from Dick O'Kane in his great book "How to Repair Your
Foreign Car" subtitled "A Guide for your Wife, the beginner, and the
Mechanically Inept" This is possibly the funniest book ever written on auto
repair.
Good luck
Rick Ewald
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