REFLECTOR: Master Brake Cylinder Bleeding

[Brian Michalk]

Two weeks ago I did some high speed taxiing and blew a brake line. This 
weekend, I replaced the lines and added inserts in the compression 
fittings, and then proceeded to bleed the brakes.

The left side bled fine and is firm.  The right side continues to pull 
bubbles in from that I assume is the primary cup seals on the retraction 
stroke.

I pulled the cylinder and took it apart.  There is a very strong spring 
that on the reservoir end pushed a rubber disc against a hole to the 
reservoir.  Pushing against the opposite end are two cup seals.  Now, 
this spring is very strong.  I think what is happening is that after a 
power stroke, the cup seals have been pushed towards the reservoir 
seal.  Releasing the pedal causes the cup seals to make a vacuum in the 
cylinder until enough force is generated to overcome the spring and 
allow fluid to flow past the reservoir seal.  Unfortunately, the spring 
is too strong, causing excessive vacuum, drawing in air across the cup 
seals.

I plan on calling the manufacturer today, but don't have high hopes that 
I'll talk to anyone useful.  To fix the problem, I can reduce the spring 
tension, or increase the cup seal force.  It's a run of the mill 5/8 
bore, so I should be able to find a lot of various seals.  Any 
experience with this problem here on the reflector?