the only way i have ever bled brakes is by pumping up and holding pressure,
and then releasing the pressure
at the brake piston bleed point. Generally this requires two people, as the
pedal/lever should be allowed to follow
the pressure and sink right out to full travel, but NOT allowed to return
until the bleed point at the brake is locked up tight
again. this is normally done as many times as needed to ensure all air is
purged from the line. Its not a bad idea to switch
brake fluid to one of a different colour if you can get it part way through,
that way you know you have pushed out the entire
contents of the line and master cylinder when you see the colour change.
Some master cylinders will self bleed to a small degree, which i bet is what
you are seeing when you stand yours on its end. Unless you have a small leak
somewhere, possibly on the seals in the master cylinder
itself, once the lines are free of air, you shouldnt have any further
problems. You also mentioned the remote reservoir, If that is tightly
sealed then once you suck a vaccum in it with the first bleed, then the
system could find a weak point and suck air around a seal or fitting.
You may laugh at this, but remember, a hydraulic brake system can have
several hundred PSI of pressure in it or more, so you could potentially be
creating a few hundred psi of suction. This would account for the level not
dropping after the first bleed.
good luck
craig
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com]On Behalf Of DR TERRY
DAWSON.
Sent: Sunday, 30 December 2007 6:48 AM
Subject: Europa-List: Bleeding Jamar finger brakes
Im having a devil of a time with my Jamar finger brakes in my
tri-gear motorglider.
I can only bleed the brakes when the master cylinders are oriented
vertically with the back of the Jamar master cylinders higher than
the front. As soon as I mount the brakes horizontally, they no
longer bleed after one effective stroke the lever no longer pumps
brake fluid.
Heres some data which may help you help me get this problem solved:
Im using DOT 5 brake fluid.
I mount a reservoir filled with brake fluid about 9 inches above the
master cylinders.
The Jamar squirts fluid from both sides when the levers are pulled
back while he Jamar master cylinders are horizontal on my bench and
when mounted horizontally in the plane.
When the Jamar is mounted in the plane and the brake lines are
disconnected from the ends of the master cylinders then the cylinders
squirt brake fluid when the levers are pulled back. However as soon
as I connect the brake lines from the cylinders to the brakes, the
brakes dont work. (This makes me suspect the problem is in the
brake lines probably air bubbles.)
When one side is working and the other side isnt, if I disconnect
the brake lines and switch the line which isnt working to the side
which does work, then that the side which didn't work now does and
the other doesn't. (I therefore again suspect the problem is in the
line rather than in the Jama but I could very well be wrong.)
I bleed the brakes in two different ways. The first way I connect a
clear tube filled with brake fluid with no bubbles to the brake
nipple. I open the nipple and, using about 20# of air pressure, blow
brake fluid up the brake line to the Jamar. I have loosened the
brake line connection at the master cylinder and watch the brake
fluid leak out. At first I get bubbles, then, when only brake fluid
is leaking, I tighten the connection at the master cylinder and close
the nipple. The Jamar system then works. The brake lever is not at
all spongy. However, over a long period of time with many
applications of the brakes, the lever must be pulled further and
further back and the brakes get spongy, needing bleeding.
The second way I bleed the brakes is by pulling back on the brake
lever while both connections (the brake line to the master and the
brake line to the brakes) are tight. When pressure builds on the
lever, I loosen the nipple and brake fluid gushes out the nipple into
the clear tube Ive connected to the nipple. I then close the nipple
and release the lever which returns to its forward position on its
own. I can see brake fluid leaving the nipple on the first stroke
and I can see the fluid level in reservoir go down.. However, on the
second pump theres no pressure against the movement of the lever, no
brake fluid leaving the nipple and no descent of the fluid level in
the reservoir. This is when the Jamar is horizontal. However, when
I have the Jamar master cylinders vertical the brakes bleed well
using this technique. (I really don't understand this at all but I
guess that air in the master cylinder is pumped out the "top" end of
the cylinder and therefore the brakes work.)
When both sides are working and mounted in the fuselage horizontally,
I try the bleed the brakes. I pull back on the lever the first time
while the nipple is open and I see fluid leave the nipple and the
fluid level in the reservoir drop. On the second pump the lever has
little resistance, no fluid comes out of the nipple and the fluid
level in the reservoir doesnt drop.
Why is it that I can successfully bleed the Jamar only when its
aligned vertically?
Id like to be able to bleed the brakes without having to orient them
vertically or having to disconnect the brake line from the master
cylinder and blow fluid up from the nipple, letting the master
cylinder to brake line connection leak.
11:51 AM
11:51 AM
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