Low brake pedal *Solved*

Topic: Low brake pedal *Solved* (Read 5414 times) previous topic - next topic

Low brake pedal Solved

February 24, 2011, 04:12:07 PM

I need some help. I've tried a lot of different things, and I can't get a good pedal brake pedal. To start off, here's what has been replaced:

Brake Booster
Master Cylinder
80% of the metal lines
All 3 rubber lines
Rear brake shoes
Drum hardware
Both calipers
Both wheel cylinders

And the old:

Rotors
Pads
Drums (we ground down the lip on them)
Proportional Valve

The car stops, but the pedal is low. With the engine running, it has about half its travel with no resistance. I can hear air coming from behind the dash when I push it in. After it goes halfway to the floor, the pedal feels fine. That's when the car stops. The pedal does not go slowly to the floor while stopped, it holds strong.

While the car is off, the brakes work as I expect them to. I pump them 3 times and the pedal is firm and high. As soon as I turn the car on, the pedal gets soft.

I have adjusted the shoes so they just barely se the drum. Didn't help. My dad bench bled the master cylinder for me, so I think that's fine. The parking brake is not interfering with the shoes. There's no brake fluid leak, the fluid level doesn't go down. My caliper's bleeder screws face upwards and towards the back of the car. The smaller shoe is in the front of the drum (towards the engine), the larger pads in the back.

If I had the money, I'd just let a professional have a crack at it...

Low brake pedal Solved

Reply #1 – February 24, 2011, 10:53:40 PM

Do you have the primary and secondary shoes installed correctly on the rear brakes?

Darren

Low brake pedal Solved

Reply #2 – February 25, 2011, 10:05:36 AM

Yup, the smaller shoe is in the front of the drum (towards the engine), the larger pads in the back.

Low brake pedal Solved

Reply #3 – February 25, 2011, 03:24:06 PM

You still have air in the system is my bet. Here is a good read for you which will make you feel a little bit better as this guy went over six months battling his problem.

http://forums.corral.net/forums/general-mustang-tech/1258481-magical-disappearing-brakes-1992-mustang.html

The more important stuff is on the third page in Post #80 where he found the problem. The whole thread is a great read as Jack Hidley (Maximum Motorsports Guru) really gets into some detail about how the brakes work on the Fox cars.

Darren

Low brake pedal Solved

Reply #4 – February 25, 2011, 04:01:33 PM

Thanks for the link, I will try that out. Well, once it stops raining

Low brake pedal Solved

Reply #5 – February 26, 2011, 02:00:10 AM

hey, arent you the guy that was trying to power up the bird c-pillar emblem and one flashed and went out?

Low brake pedal Solved

Reply #6 – February 26, 2011, 09:34:03 AM

Haha, I think we've had this conversation before.
http://www.foxtbirdcougarforums.com/showthread.php?30675-brochures!&p=352894&highlight=#post35289

Here's the thread I made if you wanna read through it, eventually I want to try building a circuit that can replicate the output of the original inverters.

http://www.foxtbirdcougarforums.com/showthread.php?27250-Electroluminescet-Emblems

Low brake pedal Solved

Reply #7 – March 02, 2011, 01:54:48 PM

Well, now that it stopped raining, I went out and got started. And I made the problem worse; I have no pedal at all now.

I started up the car to move it to a less muddy area, everything went as expected. The pedal was low, but solid after about half its travel. Car stopped just fine as it always has.

So, I turned the car off and I jacked it up, put the car on stands. I took the passenger side caliper off the car and put a block of wood between the pads, and held the caliper so that the bleeder screw was at its highest point. With my brother as the official pedal pusher, I opened the bleeder screw. Only fluid. I tried it a few more times at different angles, still just fluid.

Now here's where I probably messed something up. I went to put the caliper back on the car, but the pads were too close together to fit over the rotor. I opened the bleeder screw and pushed the pads in a little. Some air got into the system, so I realized I'll need to bleed them regularly now. So with the caliper on the rotor as it should be after a little fiddling, I go to bleed the brakes. A ton of air comes out. At first I thought this must be a great thing, but nope. A ton of air came out every time we cycled the pedal. Topping off the master cylinder every 3 or 4 cycles, the air was not out of the system even after going through half of a large bottle of brake fluid.

I noticed that the master cylinder appeared to have a lot of little tiny air bubbles in it, but only in the larger reservoir for the front brakes. I pumped the pedal very firmly for a minute or two, and the fluid in the master cylinder was pretty much white. So what did I kill this time? Caliper? Master cylinder? I don't think a leak magically opened up somewhere...

Maybe I'll just push the car off a cliff......

Low brake pedal Solved

Reply #8 – March 02, 2011, 07:04:51 PM

That sounds like a MC issue but where the F is the air getting sucked in when you are moving the pedal and yet there are no leaks??? I would disconned the lines at the MC and install the plastic block offs and bench the MC like Jack suggests in that link I posted. Start from the MC and work your way out.

Darren

Low brake pedal Solved

Reply #9 – March 06, 2011, 10:09:34 AM

Well, I solved the problem. I must have ruined the Master Cylinder while bleeding, I guess you're not supposed to push the pedal all the way to the floor when bleeding the brakes

So I replaced the master cylinder and bought a slightly nicer one. No more bubbles in the fluid and I could get all the air out of the system. But the pedal felt exactly the same. My dad said "I wonder if it's the booster's push rod. Maybe you need to adjust it." And that was it. The rod was not close enough to the master cylinder, it is a new unit after all. I had to adjust the rod out at least 2 full turns, but the pedal feels much, much better now. I've left in about 2 inches of free play, just as a precaution. I feel much better about the car's stopping ability now.

Thanks for the help Aerocoupe, I appreciate it.

Low brake pedal Solved

Reply #10 – March 06, 2011, 08:16:08 PM

That is sweet man! Glad you figured it out.

Darren