kearney
Joined: 20 Sep 2008
Posts: 563
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 Posted: Fri Feb 10, 2012 7:49 am Post subject: Leaking brake cylinder fitting |
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Hi
I installed by brakes per Van's plan eons ago. My only problem was a weeping leak at the bottom on one master cylinder that I couldn't fix. What I was experiencing was a zero pressure leak, just a weeping leak that would form a drop of fluid after a few days. Then I would get a drip on the floor pan.
To solve, I tried changing the fittings and then, at the suggestion of Matco, I used Loctite 567 thread sealant. Still no luck. My fear was I had over tightened the compression fitting and damaged the threads.
Anyway, I pulled the cylinder and installed a new one. I sent the original back to Matco for inspection.
I just had a very interesting call from Matco where they explained what happened. First, they did a zero pressure test and duplicated my problem. Them they cleaned the treads and tried again. They still had a problem.
Finally they disassembled the cylinder and really cleaned it with acetone. WARNING: don't use solvent if the rubber fittings are in place as they will be damaged. They found hardened sealant at the bottom of the fitting hole that was preventing the Loctite 567 from doing its job. They said there is a leak path at the bottom of compression fittings that the Loctite seals. The old hardened sealant was preventing this from happening. When completely cleaned and reinstalled using Loctite 567, the cylinder functioned perfectly.
Page 38-3 of the Van's plans suggest using fuel lube or a similar thread sealant to seal the fittings. Matco's recommendation is to use Loctite 567 which is a very different product. This also matches the recommendation of my local A&Ps.
The only really good thing that came out of this is I can now bleed my brakes in under 5 minutes - practise does make perfect.
As a side note, they mentioned that there was dust / debris on the top of the cylinder that accumulated during my build. They cautioned that this should be cleaned off as it could cause a problem with the seal where the shaft exits the cylinder. Although I have been cleaning fairly often, I never even thought about the top of the cylinders. It is something to keep in mind.
Cheers
Les #40643
I can almost see the light at the end of the tunnel
PS: Matco was very, very helpful throughout all of this. [quote][b]
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