G

garrys

Active Member
Every 3 or 4 weeks I have to bleed the air from my brake lines, as they get mushy and ineffective. I'm not loosing any fluid, just sucking in air. Some airport bums say it's a bad connection where the nylon (?) reservoir line connects to the master cylinders on the rudder pedals.

I'm not too keen on the cheap Nylon lines. Has anyone ever converted over to braided stainless steel flexible lines? If so, do you have a source for the lines and various fittings needed?

If by chance the airport bum theory is wrong and there's another explanation for my air sucking..........please speak up! lol

Garry Stout
Tampa, FL
 
Mine too

I had the same problem for the first two years -- affected the brakes pedals on the right side, but would have eventually affected the left side if I neglected to rid the lines of air. I replaced the plastic tee on the reservior with a BRASS TEE and have not had a problem since.

Bill Gill
RV-7 N151WP
Lee's Summit, MO
 
Are you absolutely sure you don't have a tiny leak on the pressure side? I doesn?t take much air to make it soft.

I had a chronic soft pedal on the right. Nice and hard after bleeding, but got soft after a week. Finally found a tiny leak at the fuselage bulkhead feed-through fitting. The fluid was running back along the bottom wing skin overlap and was barely noticeable. No drips or puddles. Of course, that was the most difficult fitting to get to in the entire plane. Had to grind down a wrench to tighten it up.
 
I ordered replacement lines and fitting from Bonaco today, so yes, you can convert them over.

When I first put in the plastic lines while building, I could see the air bubbles at the top of the crossover line. It took some doing to get that out of the lines. You could still have some air in the lines that worked its way to the top.

BTW, the first setup I used to pump the air into my system had the air pump in the brake fluid. Each time I pumped it up, I would put air bubbles in the fluid. I changed my pump setup and now the air pump is well above the fluid.
 
master cylinder leak

Gary,

I had the same issue when I first started using my brakes during testing, after the master cylinders had aged. I could get the lines totally filled with no air bubbles, then when operating the brakes bubbles would appear. No fluid leaks anywhere. The cylinder seals were leaking from the air side, drawing the bubbles in without leaking out. I had them rebuilt (Matco rebuild kit was only $10) and tested. After the reinstallation the problem was solved. Here is the thread that I passed along the details on.
http://www.vansairforce.com/community/showthread.php?t=50708&highlight=brake
Took a lot of trouble shooting to eliminate everything else, but successful in the long run. No issues since then and 75 hrs of operation.
 
ditto on master cylinder leak

or a leak on a seal somewhere. I was rebleeding mushy brakes every few weeks in the first 50+ hours. Rebuilt everything with new o-rings. No more mush. I still have the plastic T and plastic lines on the pax side of the system.

Bon Chance.

Don
 
Found this problem on a corvette. check that there is no rotor run out, (warped) the pulsations on the caliper piston can pump air into the system with no pressure being applied to the hydraulic side of the seal in the caliper.
 
Brake bleeding

I put bleeder screws at the high point on the cool side of the firewall during building. Bleed from the pedals up and blled from the wheels up. Never used them again Yet!! Do'nt have any brake pedal problems.
I have aluminiun lines down to the wheel and used swaglok fittings.

ZK RVG
 
You would think the air being sucked in would displace the fluid somewhere. Is the reservoir more full now?
 
The air leak on the reservoir side of the master cylinder, which is what I describe above, does displace the fluid in the reservoir, but this is a very small amount. You can get spongy breaks from the air bubbles without significantly affecting the actual level in the reservoir, although you are correct in that the bubbles will displace a small amount.
 
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