Parking brake on runup holds at 1500 but not much above that

[Senseipilot]

PA-22 1954 with O290-D2. Original brake system. Reservoir is full. I fly from a grass strip. My parking brake holds fine at 1500 RPM, but the plane starts inching forward if I try to get to 1800. The brake pads are new. Anyone else have this? I haven't been able to find a thread that addresses this.

[stevesaircraft(Bri)]

Diaphragm and drum brakes. Adjust your drums to almost dragging. Diaphragm only puts out 350PSI at 100 pounds of peddle pressure. A booster master more than doubles the braking pressure but you are still limited to the drums. Ultimate setup is update to disks with a booster master cylinder.

I have STC’s for both.

—Brian

[walt.buskey]

And -- if you have the OEM drum brakes (which have "shoes," BTW, not "pads"), you might check to see if your felt-ring grease seals are leaking and allowing grease to get on the brake shoes.

[Steve Pierce]

Can it hold with the brake handle but just doesn't hold when you use the parking brake or just doesn't hold. Disc brakes need a break in of several cycles of dragging the brakes and get it hot and then let it cool.

[Frank Green]

You say you replaced the "pads" Meaning the linings on the shoes. Who did it and what did they use? A local "brake" shop would only have hard material used on cars. I made my own and there are different coefficient of friction pad materials. I used a fairly aggressive material from McMaster Carr and on grass landings I can lock the tires. They are actually used so little I don't worry about drum wear. The old pads were as hard as concrete after 60 years. Way cheaper than switching to discs and you actually have 3 times the amount of pad surface.

[dgapilot]

parking brakes are for one thing only, holding the airplane still long enough to put chocks under the wheels when you park! you shouldnt be using the parking brake for run up. read the placard that says the hand brake doesn't work when the parking brake is applied!

[Frank Green]

Missed the "parking brake" part in the first post. Yep what dga said. One other thing is be sure to keep an eye on the cable where it goes around a 1" pulley behind the rudder cable. If it breaks there it will make your heart beat up a tick. Also if you blow the master cylinder diaphram. Glad I had a lot of runway in front of me.

[Scott M]

Aplogies in advance for the thread detour but I would love to hear more about Franks McMaster Carr purchase. Do you remember what part number you bought ?