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Brakes

 
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chasb(at)satx.rr.com
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PostPosted: Sun Oct 27, 2013 11:29 pm    Post subject: Brakes Reply with quote
My RV-6A is equipped with dual brakes with Van's parking brake. Been flying for over six years with no problems. Recently I discovered that the copilot brake pedals went to the floor and provided no braking. Fortunately, the pilot side brakes worked and felt normal. Pumping the brakes from either side didn't change the situation. Investigation showed the copilot brake lines had no brake fluid in them, and the brake reservoir and its connecting lines were also empty of brake fluid. But, I can find no evidence of any leaks or spills. I drained both left and right brakes of fluid and refilled both systems. Both pilot and copilot brakes now work normally and I still can find no evidence of any fluid leaks.

But the mystery remains, where did the fluid go, and why was only the copilot brakes affected? Has anybody had a similar situation?

Charlie Brame
RV-6A, N11CB
San Antonio

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carl.froehlich(at)verizon
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PostPosted: Mon Oct 28, 2013 5:15 am    Post subject: Brakes Reply with quote
The copilot brakes are in series with the pilot - so as fluid is lost in the
system and the brake reservoir goes dry, they will run out of fluid before
the pilot side (but not my much).

Brakes are not a perfectly sealed system, leakage can happen.
Checking/topping off the brake reservoir every time the top cowl is off is
the best way to find out if you have a problem. It is hard not to have some
air in the reservoir return lines on initial fill. With time this air will
work its way out. Assuming your problem is one where there was no reservoir
change for a long time and now it is empty, I would first look at the brake
line fittings and then to the brake piston "O" ring. These do need
replacing from time to time and if they leak slow enough the fluid just adds
to the grime inside the wheel pant. If you have six years on your plane it
might be time.

On the RV-10 I had a dragging brake problem on one side. I found the piston
"O" ring had rolled (110 hours on the plane). This prevented the piston
from retracting and created some leakage as well. In just few hours like
this that gear brake pad was gone and the tire was ruined as well.

Carl

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vanremog(at)aol.com
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PostPosted: Mon Oct 28, 2013 6:37 am    Post subject: Brakes Reply with quote
Just a working theory offered for your consideration.

IIRC the stock Van's brake system is connected as a cascade arrangement that places the passenger master cylinders in a position closest the fluid reservoir. Mine is not connected this way and uses shuttle valves instead. Any downstream leak (say for instance that you haven't changed out your caliper nitrile O-rings for Viton and they are slowly seeping) would cause fluid loss and as the last of the fluid in the reservoir is sucked thru the supply line the passenger masters are next in the series chain.

Check it out. Very small leaks over a long period of time can have a big effect. As Neil Young says, Rust Never Sleeps and the same can be said of the death by a thousand cuts scenario.

-GV (N1GV)


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denis.walsh(at)comcast.ne
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PostPosted: Mon Oct 28, 2013 6:55 am    Post subject: Brakes Reply with quote
The situation you describe is the way leaks are discovered in Van's system.

1. Keep looking for the leak. Check all connections. If you have found no drips, then it may well be only leaking under pressure, or return pressure when the brakes are released. Check for these "pressure leaks" by looking at all fittings while applying pressure. If you have carpet, check very closely for stains. this will give you a clue which side is leaking. If it is leaking at the brake, it will usually evidence as drooling on the bottom of the wheel pants, but if no stains in the cockpit, you need to remove pants and check both sides under pressure.

2. Always check the brake reservoir each time you remove the cowl. It should never be down more than 1/3 due to normal pad wear.

3. My best guess would be that if the parking brake holds, then you have a master cylinder needing overhaul.

Good luck. I repeat, keep looking for the leak, because you got one.
DLW
On 28Oct, 2013, at 1:29 , Charles Brame <chasb(at)satx.rr.com> wrote:

Quote:


My RV-6A is equipped with dual brakes with Van's parking brake. Been flying for over six years with no problems. Recently I discovered that the copilot brake pedals went to the floor and provided no braking. Fortunately, the pilot side brakes worked and felt normal. Pumping the brakes from either side didn't change the situation. Investigation showed the copilot brake lines had no brake fluid in them, and the brake reservoir and its connecting lines were also empty of brake fluid. But, I can find no evidence of any leaks or spills. I drained both left and right brakes of fluid and refilled both systems. Both pilot and copilot brakes now work normally and I still can find no evidence of any fluid leaks.

But the mystery remains, where did the fluid go, and why was only the copilot brakes affected? Has anybody had a similar situation?

Charlie Brame
RV-6A, N11CB
San Antonio






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panamared505(at)brier.net
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PostPosted: Mon Oct 28, 2013 8:57 am    Post subject: Brakes Reply with quote
If you do aerobatic stuff, you will lose brake fluid as you go negative.
Need an inverted brake cylinder.

Bob
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