REFLECTOR: Master Brake Cylinder Bleeding

[steve korney]

Are both the cup seals facing the same way..?   Maybe you can turn one around so they seal in both directions...


Steve 

> Date: Mon, 8 Oct 2012 10:34:47 -0500
> From: michalk at awpi.com
> To: reflector at tvbf.org
> Subject: REFLECTOR: Master Brake Cylinder Bleeding
> 
> 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?
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