02 Explorer Brake Question

[beertracker]

Need some brake advise. It's a 02 Explorer, ABS and 4 wheel disk brakes.

My brakes were working fine on the Explorer then yesterday morning I started it up and the brake pedal pretty much goes to the floor. I can still stop the vehicle but it doesn't seem safe; too much brake travel and on the spongy side.

With the Explorer off, I can pump and the pedal slowly goes to the floor but as soon as I turn it on, the pedal goes to the floor.

What about air in the brake lines? I checked the master cylinder and it was filled to the FULL mark. If it is air in the lines how did air get in? Do you recommend a brake bleed?

I didn't see any brake fluid leaks at the master cylinder or wheel cylinders.

The truck has about 140K on it and the fluid has never been changed as far as I know. I wish I knew what caused this failure?

What other brake components between the master cylinder and caliper could cause this problem and how would they be tested?

The last thing I tried was replacing the master cylinder with a new one and the problem still exists. I bench bleed the master cylinder before installation and kept the reservoir full of fluid.

Thanks,
bt

 

[bizzs]

Beertracker,

I had a problem similar to yours years ago after I replaced both front calibers on my 03. You need an assistant to help out pumping the brake pedal and holding it to the floor while the bleeder is opened on each one of the wheel cylinders and calibers.

Start the cycle from the far right passenger side and you will see the air squirt out of the bleeder when opened.(Search google for assistance of this procedure.)

I have a snap on solus scan tool and the software is bi-directional. It instructs the computer to allowthe ABS system to cycle the pump and bleed the brake system automatically giving a hard pedal.

It appears that you did the right move by replacing the master cylinder, but I would check all of the brake lines to see if there is a small pin hole leak somewhere.

Hope this helps,
bizzs

 

[beertracker]

I bled the brakes today and the passenger rear had a lot of air in it. As long as the engine is off I have a firm brake pedal as soon as I start the engine the pedal goes to the floor and won't pump up firm.

Bizzs, thanks for the info. Maybe the ABS has something to do with my problem. More work tomorrow.

bt

 

[Junkmann2]

What condition was the brake fluid? If it was dark, then you probably have a sludge problem in the braking system. Brake fluid should be changed every 2 or 3 years, and flushed out of the system with new brake fluid. I'm betting that you have a bad master cylinder, and that the fluid is passing from one chamber to the next, rather than building pressure. The dual master cylinder acts like two separate cylinders, with a rubber membrane between the two halves. This membrane moves with the piston inside the master cylinder. Eventually they wear out. I would suggest a new or rebuilt master cylinder and a complete brake fluid flush. Also change the front and rear rubber hoses, if they are original or old. They don't last forever, and they deteriorate from the inside, causing blockages. Also check the metal lines for signs of rust on the outside. Depending on where you live, some states use a very aggressive deicing compound on the roads. These products cause all types of rusting problems.