Brake pedal movement.

[Nathan K. Hammond]

J-3
Original master cylinders
Grove brakes.

After nearly going for a swim in Ohio, I installed new pads and topped off the masters with 5606 last night. Did the trick of pulling the pedal back as far as possible while filling the reservoir. But now I've got about 1/4"-1/2" of pedal travel before they get firm. It's not squishy, as if air is in the line, more like there's air trapped in the reservoir. The brakes work great now, but in order to get on both brakes hard, I have to bend my toes backwards or dance the brake/rudder back and forth.

I've lifted the tail, gone flying, everything I can think of; but when I pull the cap, fluid is at the top. Anybody have an idea why the pedal is moving before it gets firm?

nkh

 

[behindpropellers]

J-3
Original master cylinders
Grove brakes.

After nearly going for a swim in Ohio, I installed new pads and topped off the masters with 5606 last night. Did the trick of pulling the pedal back as far as possible while filling the reservoir. But now I've got about 1/4"-1/2" of pedal travel before they get firm. It's not squishy, as if air is in the line, more like there's air trapped in the reservoir. The brakes work great now, but in order to get on both brakes hard, I have to bend my toes backwards or dance the brake/rudder back and forth.

I've lifted the tail, gone flying, everything I can think of; but when I pull the cap, fluid is at the top. Anybody have an idea why the pedal is moving before it gets firm?

nkh

What do you have for hoses in between the master and the line on the legs?

 

[mike mcs repair]

yup you have a bubble trapped, very hard to remove...
completely drain fluid and blow out with air compressor to get rid of bubble, then refill from bottom, at fast rate too....

 

[mike mcs repair]

also you sure you put right pads on, and they are not hitting or binding/bending caliper at first, this will show as funky at first till you 'press' on them and they take up the slop

 

[bob turner]

What Mike said. Some facilities have pressure bleeders that can flush these things out really quickly. But for most of us, just drain completely, then fill from the bottom, using a hose at the top into a jar. Have a girl on top watch to make sure no bubbles come out of the top after about 30 pumps on the can at the wheel.

By the way, those pumper oil cans are not getting any better - keep your eyes peeled for the older large NAPA can. You have to machine the nozzle to fit the hose.

 

[Nathan K. Hammond]

New lines a couple years ago.

Correct pads and installed correctly. Slop was removed after first push of the pedal.

I guess bleeding them up is the next step. Mike, why do you flush them with air?

nkh

 

[skywagon8a]

I guess bleeding them up is the next step. Mike, why do you flush them with air?

When the complete system is not blown out with air, an air bubble can (but not always) become trapped somewhere. Then when you bleed it the fluid runs around the air bubble. The fluid will run clean out the top leaving you to think that it is clear. The air bubble will still be down inside somewhere so that when you step on the pedal the air will squish, thus poor brakes. This problem is more common on planes with brake lines that have a level routing or with a hump in it somewhere. Think about the air bubble which floats at the high point so that the fluid runs under it.

 

[cruiser]

Another .org'er suggested a pump made out of a windshield washer bottle with integral pump and raising the tail of the airplane to sort of level things out for flow. That solved my soft pedeal. Jim

 

[bob turner]

What Mike says makes sense. We had a recalcitrant Super Cub a while back with Blue River/ single puck (like Grove). Nobody could make it work. All we did was let every drop of fluid out, and pump it back in from the bottom. Presto.

Doesn't cost much, because you can re- use the fluid on brakes without complicated check valves.

Lately I always hook the tube on the top - a clear tube, so I can see what is going on. Think fish tank, or model airplane fuel line.

 

[behindpropellers]

I used to use the pump from the bottom method....

Now I use the suck from the top method with a vacuum oil changer pump I have. If you do it this way, you do not get any bubbles in the system.

Tim

 

[mike mcs repair]

I used to use the pump from the bottom method....

Now I use the suck from the top method with a vacuum oil changer pump I have. If you do it this way, you do not get any bubbles in the system.

Tim

?????? pictures????

 

[Monte]

What fitting do You use at the top of the master cylinder to hook the hose to?

 

[Roger Peterson]

Tim, I think that is the best idea I have heard. Really hard to pump pure fluid and never get a bubble.

 

[mike mcs repair]

i would think any SMALL leak(too small for even fluid to leak, maybe just a stain) might suck in air with the vacuum method???

never tried it for this.. just thinking out loud...

but fought that(sucking air in while trying to suck fluid in strut) allot on front struts of edo anphibs with those floating pistons and old cleavland bleeder valves....

 

[Roger Peterson]

i would think any SMALL leak(too small for even fluid to leak, maybe just a stain) might suck in air with the vacuum method???

never tried it for this.. just thinking out loud...

but fought that(sucking air in while trying to suck fluid in strut) allot on front struts of edo anphibs with those floating pistons and old cleavland bleeder valves....

Mike, off subject, but just timed my new plane with the cell phone method and worked great. Used a app that spoke the deg so it was real easy.

 

[bob turner]

I rarely have serious problems, but that Super Cub I mentioned got me. We put reservoir masters on it, and I never did get enough air out to make them safely work. I put the North Rivers back on and had them working in ten minutes. Then I made a test setup with identical calipers, same lengths of copper and rubber, etc., and had the test setup bled on the first attempt. Maybe it has loops inside the covered gear legs.

I drained and filled, drained and blew out and filled, hooked on to the master and ran a gallon through from the bottom as fast as I could, ran the same gallon through as slow as I could - never got it. Gave up.

Today a different problem on a J-3. Grove brakes. Wouldn't grab. Looked at caliper - no problems obvious. Putnew pads on. Wouldn't grab. Scuffed the disc. Wouldn't grab. Loosened the caliper to make sure the piston was working. Not working. Looked at master. Not moving. Replaced master. Not moving.

It was the pedal itself. It had been gouged out and would lock before it pushed the piston rod. Never seen that before. This was the pedal/master cylinder with the least number of landings, so I can only assume a casting flaw. Will polish it up tonight and test tomorrow.

 

[mike mcs repair]

Mike, off subject, but just timed my new plane with the cell phone method and worked great. Used a app that spoke the deg so it was real easy.

cool! I never did finish that project.... one of my many "started" projects...

 

[skywagon8a]

I rarely have serious problems, but that Super Cub I mentioned got me. We put reservoir masters on it, and I never did get enough air out to make them safely work. I put the North Rivers back on and had them working in ten minutes.

Bob, Here are a couple of pictures of the North Rivers with a reservoir installed.

The filler cap was replaced with a manual needle valve from ACE. Very simple, easy to bleed.

 

[Gordon Misch]

Bob, Here are a couple of pictures of the North Rivers with a reservoir installed.
View attachment 9893View attachment 9894
The filler cap was replaced with a manual needle valve from ACE. Very simple, easy to bleed.

Looks like a real good idea. Also looks like a minor alteration?

Also, looks like a ball valve on the output of each cylinder - parking brake? Can you reach that from the seat?

 

[skywagon8a]

Looks like a real good idea. Also looks like a minor alteration?

This one is in a homebuilt however, I see no reason why it could not be a minor alteration or on the original 337 with a deviation.

Also, looks like a ball valve on the output of each cylinder - parking brake? Can you reach that from the seat?

That is a 1/8"npt stainless ball valve (special order from ACE). It is in the same location as the original Scott valve and is reachable while in the seat.

The reservoir was made from a 2" diameter piece of plexiglas rod. Turn it slowly on a lathe.