Cessna 210 brake issue.

[Ron Stowell]

Evening all, I have a Cessna 210L in the shop. This AC has all new hydraulic hoses, power pack. The right brake if you with force use the right brake its rock solid. No leaks anywhere. When you lightly depress the bake the pedal goes to the floor. Then second pump its solid. This brake has new o rings at the caliper, new o ring on the 45 fitting on the top of the caliper. New o rings in the MLG bolt at the upper gear let attach point for the pass through of the brake system.

New swivel fittings on both for the brake system. And a new from Textron right brake master cylinder. Bled the brake several times, bottom up and top down. New vent cap. Any other with this problem??

 

[Bell206]

The right brake if you with force use the right brake its rock solid. No leaks anywhere. When you lightly depress the bake the pedal goes to the floor. Then second pump its solid.

Usually when pedal application forces cause a difference in braking action it is an internal master cylinder issue. And is normally due to harden seals. What was the shelf date of the new master?

 

[NordicDave]

Usual suspects are air in the brake line, flexible brake line expansion, fluid bypassing internals of master cylinder.

Easy for bleed lines to have air reintroduced through fittings and defective brake pistons or master cylinder. Incorrect fluid causes issues as well, though not likely from the description of symptoms. Maybe an O ring is rolled?

Bleeding that brake side again would be telling from a diagnostic standpoint.

 

[Let'sgoflying!]

Light pedal force makes it bleed down.
Heavy force, it holds pressure.

Sounds like an o-ring is not doing its job well; it expands and holds well if it is suddenly jammed, but is not making good contact at rest.

 

[Dan Thomas]

On the 210 there are no hoses on the caliper end of the system. If those solid aluminum lines get bent while the caliper is off, once they're reattached they can put a bit of outward force on the caliper, causing the piston to move inward and move fluid up into the master's reservoir. Then it will take an extra pump to close the lining/disc gaps up again before you get a hard pedal. So now you need to disconnect that line and see where it wants to rest. If it's outboard of the fitting, bend it back so it's a little inboard of the fitting, to keep the outboard lining against the disc and avoid any pressure on the inboard lining and piston.

Sometimes this shows up only while taxiing or after a flight. The vibration enables the movement of that piston more easily.

 

[Rob58]

On the 210 there are no hoses on the caliper end of the system. If those solid aluminum lines get bent while the caliper is off, once they're reattached they can put a bit of outward force on the caliper, causing the piston to move inward and move fluid up into the master's reservoir. Then it will take an extra pump to close the lining/disc gaps up again before you get a hard pedal. So now you need to disconnect that line and see where it wants to rest. If it's outboard of the fitting, bend it back so it's a little inboard of the fitting, to keep the outboard lining against the disc and avoid any pressure on the inboard lining and piston.

Major kudos to Dan for this rather brilliant observation. After a complete overhaul of my brake calipers I noticed something very similar to the condition reported by the OP. I have a flexible hose which attaches to my caliper, not a hard line. In the domain of unintended consequences I discovered this: the pins that allow the brake assembly to move in and out on the torque plate where dirty prior to the overhaul and thus did not allow the moving liner plate or the pistons to retract without some positive force. However once these pins were cleaned and lightly greased even the small amount of force exerted by the brake hose cause the pistons to retract just enough to require a little extra pedal movement on the master cylinder. This can be rather easily observed with a flashlight. Mystery solved... thanks Dan! Of course Dave's comments (both "Daves") are golden as well.

 

[Dan Thomas]

Major kudos to Dan for this rather brilliant observation. After a complete overhaul of my brake calipers I noticed something very similar to the condition reported by the OP. I have a flexible hose which attaches to my caliper, not a hard line. In the domain of unintended consequences I discovered this: the pins that allow the brake assembly to move in and out on the torque plate where dirty prior to the overhaul and thus did not allow the moving liner plate or the pistons to retract without some positive force. However once these pins were cleaned and lightly greased even the small amount of force exerted by the brake hose cause the pistons to retract just enough to require a little extra pedal movement on the master cylinder. This can be rather easily observed with a flashlight. Mystery solved... thanks Dan! Of course Dave's comments (both "Daves") are golden as well.

Even that hose can exert significant outward pressure if its geometry is about right and the B nut is tightened so that the hose exerts a twisting force on the caliper that can move it outward. It helps if you collapse the piston a bit by pushing outward on the caliper, then playing with it a bit to see if it wants to spring outward. Loosen that hose nut and let the hose relax a bit and retighten. Sometimes you need to hold the hose assembly so the tightening nut doesn't twist it. Old hoses are also stiff and can cause more trouble.

The hard lines often get bent because the mechanic didn't disconnect the brake line to replace the linings. He pulled the caliper out far enough that the pins came out of the backplate to let the inboard lining come off, and then when it was pushed back in, that aluminum line now has a built-in outward spring to it.