Right brake locked (72 GCBC)

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gregpwyatt

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May 9, 2021
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wyoming
Any idea how to release the brake on one side? Gremlin must have set it. The parking break cable was partially engaged. Went to move it and tried to release the parking break and the cable moves like its working but will not release the break. How do you access it? I just want to do away with the dam thing. never ever used the one in my Husky
 
That's why in another thread about brakes I asked about pre-landing checklist items including "parking brake off".
Landing with the parking brake on allows you to put the brakes ON but when you release pedal pressure the caliper(s) doesn't let go...
Chris
 
What mostly happens is the pressure between the parking brake valve and the caliper make the parking brake valve arm hard to move. Add a marginal or poor installation of the push/pull cable allowing it to bend and flex instead of pushing/pulling and the parking brake gets stuck in the ON position...
Chris
 
Lately I have taken to using the one in my Decathlon. I crank it up, taxi about 50 feet from my hangar to the runup area, set the parking brake, and then buckle in my parachute and harness while the engine warms up. It's handy.

How would a parking brake get set in flight?
 
depress the brakes and pull the handle?

I saw a CFI reach in and push the rudder pedal by the door before pulling the parking brake handle. He did it by the fuel pumps and I've adopted it for myself when I'm on level ground and want some brakes applied for fueling or a walk-around.
 
Big Ed said:
Lately I have taken to using the one in my Decathlon. I crank it up, taxi about 50 feet from my hangar to the runup area, set the parking brake, and then buckle in my parachute and harness while the engine warms up. It's handy.

How would a parking brake get set in flight?
Click to expand...
It really depends on the type of brake valve. The "spool" type of valve used in some WW2 birds (A20 and B25 come to mind) would only block in the vent "release" direction... to set the brakes you could either do the pedal press/pull the PB handle -or- pull the PB handle THEN push the pedals...the spool allowed hydraulic pressure into the brakes but it couldn't get out. 😳. I've seen that type of arrangement on civilian planes but I don't really recall which ones...Cessna's I think...
Then there are the brakes on Grummans; they have a locking tab on each brake master that actually locks the shafts on the master cylinders. With that you pull the brake handle and depress the toe brakes...the tabs keep the cylinder shafts from releasing. As you can imagine, most of these have had the pull chains cut and the parking brake placarded "INOP" .
In our planes I think the PB would have to be manually set or somehow migrate to the closed position. I don't think our type of valve (port blocking) would allow the brakes to self-set.
I do wonder if, with the Parking Brake pulled, can you apply the brakes at all? That might prove an interesting experiment.

Chris
 
Chris, you're right about our brakes, they work like a check valve that is held open by a cam action in the valve body. When the brake is off the ports are being held open and the brake fluid flows through the parking brake body to the calipers. Pulling the handle rotates the cam action shaft and the spring loaded ports are allowed to close blocking the fluid from returning to the reservoirs. Older valves had ball bearings that seated against o-rings, the new ones (early seventies I'm guessing) had a piece in there that was designed to sit on the spring and seal against the o-ring. I forget what the parts diagram refers to it as.

I think if the parking brake were set you could apply more pressure to the calipers even though the pressure would work against the springs to open the ports and unseat the check valve components.
 
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The other day I was doing a run up and decided to see if the PB was strong enough to hold. When I got above 1600 RPM the aircraft began creeping forward. Additional pressure on the pedals stopped the motion. Based on that behavior, the answer is yes.
 
if anyone needs a parking brake valve, i have two extras from my project. one is the ball bearing type, the other is the newer style. both need o-rings but they're complete and ready to be reassembled and put back into use. accepting reasonable offers. ;)

photos in the for sale listing show the parts that we're discussing above

Gerdes A-850-1 Parking Brake Valves FS

Have two for sale, see details below, both were lightly cleaned with 100LL and a vinyl bristle brush. First one is the later style that uses machined plugs for the check valves that make the unit function. Includes the inlet AN fittings and a new snap ring. O-ring kits are available from...
champcitabriadecathlonforums.com champcitabriadecathlonforums.com
 
Well, living in Louisiana it's easy to forget the whole world ain't flat as a fritter (pancake to you Yankees and others).
Parking brakes are seldom needed around here...though I could see wanting one if I were in the more lumpy parts of the Country...😳

Chris
 
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