Brake fade and recover ....

[Jim Sower]

Hey all,

I'm trying to troubleshoot my brakes on my Velocity FG (Clevelands driven by Nissan clutch

master cylinders). When I start out, they are pretty good. Not crisp and stiff like I'd prefer,

but they stop and steer acceptably. On landing, particularly when I brake hard to make the

midfield turnoff, they fade and go almost to the floor. I have pretty marginal steering back to

the hangar, but they're back OK the next day (or after a couple of hours rest on turnaround.

There's no fluid loss. Just very bad brakes after a hard use that come back to not good, but just as adequate as they ever are.

 

The bleeding nipple is on the top of the caliper so they have to be bled down from the master

cylinder, and I know that's bad and I'm going to change it so I can backflush the system and

move the bubbles out in the direction they want to go anyway instead of oscillating them up and

down in the strut.

 

Anyway, I had a failure last night. After fading on rollout, they steered back on the taxiway but

the right side failed utterly in front of the fueling station. I had to shut down to stop at all. It did NOT come back at all after fueling.

 

What I can't figure out is where and how the failure could be happening if there is no loss of

fluid. I'm leaning toward the master cylinder since that's the only place I can imagine at all that could switch back and forth between adequate and bad with no fluid loss.

 

Everything together seems to contradict Mr Newton.

Why does this crap always happen to me?? Jim S.

[unick3]

I am confused. Is it just you peddle goes to the floor (have you tried pumping it? which would indicated air in the system, or is the brakes just fading you (due to heating up) when you land. To me it seems like we need to define is it brake fade or peddle drop... or both...

[unick3]

For kclongez...

 

You may want to check where your brake line may be heating up near the rotors

and causing a soft area in the lines. Just a thought, I'm not familiar with

the brake system on a Velocity.

 

Good Luck,

 

Kerry

[unick3]

From Jim S

 

From the fuselage out to the calipers, Velocity is the same as EZ, Cozy. I did check that and found no sign of "aneurysm". I don't know, but my guess is that nylaflow would rupture before it would "stretch" very much. Otherwise, how would

it be useful as brake line?

 

Thanks for the heads up .... Jim S.

[Jim Sower]

<... peddle goes to the floor (have you tried pumping it? which would indicated air in the system, or is the brakes just fading you (due to heating up) when you land....>

 

Both actually. The pedal starts out OK, but as I slow down, it gets lower and fades. Doesn't seem to go all the way to the floor, but close. If it's true that air in caliper will expand when hot and the increased volume will allow more pedal, then that's what's happening. however, that diesn't make much sense, because the air in the caliper is trapped, and to increase volume, it must also *vastly* increase pressure, which would have the *opposite* effect. Just compressing the air in the caliper back to its original volume would require a great deal of pressure. The hotter the air, the more pressure would be required to keep it at it's original volume. But my brake pedal gradually drops toward the floor during rollout.

 

I'm shotgunning it now. I have inverted the calipers and rebuilt the master cylinders so far. I am going to bleed some more and see what happens. If I can find an appropriate fitting, I will stop up the cylinder and see if it holds hard pressure in the master cylinder without leaking.

Get's confusing .... Jim S.

[John Slade]

Jim

Lets have the "rest of the story....."

[unick3]

I had a similar problem. The peddle would go all the way to the floor but when I pump the brakes a few time they would "pump up". Only occurred when I had the wheel pants on. As it turned out the wheel pants pushed on the brakes slave cylinder and caused the fluid to be forced up into the master cylinder.

 

1. Do you have wheel pants.

2. Have you disassemble the master/slave cylinders and checked the seals? You could have corrosion in the cylinders causing leakage.

3. Air will cause a fade until the bubbles are compressed. Pumping the brake peddle will test for this. Heating and cooling does not make a difference to the pressure.