Parking Brake Valve trouble potential

[SierraYankee]

Dear Skymaster pilots and mechanics;
what are the possible troubles a malfunctioning parking brake valve (the entire unit) could cause ? This is for a P337H, SN P33700305
Could a leaking valve cause brake pressure loss in both L & R sides ?
Could a 'broken' valve cause air to entrain into hydraulic lines, or oil leaks.

Any conceptual thoughts would be of help.

Thanks in advance

[mshac]

My understanding is the parking brake valve closes the brake line while pressure is held on the brakes, allowing the brakes to stay "set", with the pressure remaining in the line.

A failed parking brake valve would potentially keep you from setting the parking brake, but unless its also leaking fluid, I don't see how it could affect your brakes.

Attached are a few relevant pages from the P337H service manual:

[SierraYankee]

Thanks for the informative reply and relevant pages.

Can the parking brake valve (if physically damaged) cause air to be entrained in the brake lines ?
My brakes keep losing pressure and oil, and every 4th-5th landing the master cylinders need to be replenished. No oil on the floor or belly (unless it is squirting out on the runway during landings).

[mshac]

It certainly could. Have you removed the cover panel and inspected the valve for leaks? That brake fluid is going somewhere. You may find your sound deadening fiberglass near the valve is saturated with 5606.

[SierraYankee]

No oil leaks evident from the brake valve

[mshac]

5606 is red out of the can, but if exposed to air and light it will turn clear. I would take another hard look a the entire brake system. Any fluid could be your leaking 5606, and it may not be obviously red.

[SierraYankee]

Greetings Folks;
anyone have a diagram or sketch of the C337 parking brake valve.?
Need to see if a worn valve could leak 5606 fluid simultaneously from both Left and Right hydraulic lines.
THANKS in advance

[Dan schultz]

Yes it can if the seals are bad. Mine had a bad bore and I sleeved it. Make sure to undo the fittings to get the small pins out so you can pull the actuator rod out. The actuator rod has the seals on it.

[SierraYankee]

Thanks for the info Dan.

[Kim Geyer]

I’ve had to reseal several valves. As a matter of fact I had a spare valve I would rotate around

[Charlie Lyford]

Hello,
I went through this on my P337. The parking brake valve can leak internally but not let fluid out. With one of the reservoirs being higher than the other the fluid gravity drains out of one and over fills the other. You will find the missing fluid in the insulation outboard of your left foot, it will hide a lot of fluid. New seals in the valve stopped the problem.

[Learjetter]

This is applicable to 337 G & H models with the lever-type parking brake handle.

The service manual and the parts manual have no procedures to rebuild the parking brake valve. So my buddy dared me to open it up and see if it's rebuild-able. It is, with standard o-rings suitable for 5606 fluid.

Use Service manual procedures to remove the valve from the aircraft.

Remove two lower hydraulic fittings, exposing valves, rods and springs. Remove circlip from cam lever and pull cam out. Replace 7 o-rings and re-assemble in reverse order, then reinstall in aircraft per service manual.
Good wrenching!

[SkyMac]

Hi

Same as learjetter, found it difficult to find info, ended up using a diagram from McFarlane for what i considered was an identical valve they were selling which described parts (O rings), with the clear images, I decided to remove and rebuild.

Why, fluid bypassing valve and overfilling lower reservoir, every few months I was refilling the top reservoir. Found the insulation to be soaked in oil when I removed the carpet.

It’s actually quite a straight forward rebuild, took about 30 min, made sure dual inspections were done before final assembly. Longest time was removal and reinstalling the valve.

I also purchased another valve and rebuild that unit for a spare. O-rings are only a few dollars.