cessna 210 mushy brakes

[henryinparadise]

1973 Cessna 210 has 1 mushy brake. No external leaks. Lock o seal has been replaced. Lines have been
bleed many times. At times it works fine. At times very poorly. Mechanics are stumped. So am I?
One pattern is: After bleeding the brake its great. Then after flying that brake seems to go mushy.
Is it possible that something about flying can put air in the lines?
Any ideas out there? Thanks for any input.

 

[unsafervguy]

first guess is master cyl's need to be rebuilt.

 

[Clip4]

You may have a leaking brake pivots or ,although not that common in 210s, you may have a cracked landing gear pivot assembly.

Easy to determine if this is the issue. Open up the floor and see if you have fluid present. You also might see hydraulic fluid dripping from the drain holes in the belly near the main gear.

Cessna Flyer Association - Q&A: Leaky brake pivots, and landing gear maintenance and inspection for Cessna 210s

Landing gear maintenance and inspection for Cessna 210s

www.cessnaflyer.org

McFarlane Aviation SWIVEL ASSEMBLY - Part Number: MC1280111-1

FAA-PMA parts for Cessna, Piper, Grumman, and Beechcraft aircraft. Products include cables, engine controls, steering rods, seat rails, engine controls, rudder pedals and many more airframe parts.

www.mcfarlaneaviation.com

 

[Anthem]

ive been told this is frequently a brake master cylinder needs to be rebuilt or checked (sometimes they dont hold ) - although if it works after being bled/flushed - then that might eliminate the master brake cylinder.

 

[Dan Thomas]

Look carefully at the caliper on the problem side. Does it have a metal hydraulic line to it? If so, that line may have been distorted when the mechanic had the caliper off to replace the linings, and the line is pushing the caliper outward, which pushes the piston inward and makes the brake pedal go low until you pump it up. This will often happen during the vibration of takeoff and landing, and the brake will stay OK otherwise when the airplane is sitting still.

The fix is to get that line re-formed so it doesn't push that caliper around, or try to twist is so the linings wear unevenly. Disconnect the line, bend it so it lines up with the caliper's fitting properly, and reconnect it. Might have to bleed the brake again.

Clip4's suggestion of the leaking pivot fitting is valid, too. It doesn't show in that diagram. It's a small hydraulic fitting that screws into the inboard end of the swivel. Expensive, too. That's in addition to the seals and stuff shown in his diagram.

 

[Clip4]

Shown now.

 

[Steamflyer]

1) vacuum bleed seems to work better
2) brake swivels are often a problem - can be replaced if needed
3) master may be tired and need new o-rings

If the system is not working right in a 50 year-old aircraft, I’d do all three at once. Very expensive and downs the airplane repeatedly to scattershot the fix.