More Brake issues- intermitent pedal issues

[dickeypjeep]

My GF's 92 ford explorer had horrid brakes (there was a metal ring that was the outside of the rotor that fell off when I checked the brakes... scary!), so I replaced all 4 wheel's brakes. Calipers, wheel cylinders, rotors, pads, shoes, and wheel bearings. The front lines looked old but not terrible. I bled the system fully twice.

I took it around the block after doing this and adjusted the rear brakes until I felt like the pedal was about right. I also checked each brake for heat to make sure they were all engaging.

The car seemed great after this- brakes worked well, no problems. But now twice the pedal has just gone to the floor on her without the brakes engaging at all- no resistance, no stopping. She pumped them the first time and the brakes came back. The second time she pumped and pumped with no success, so she had to use the e-brake to stop and park the thing.

I had her check for leaks 45 minutes after this second time and there were none, but the brakes had magically returned to fully functioning .

I'm thinking its got to be the master cylinder, but I've never seen one fail personally so I don't know the symptoms. Am I right or is some ABS nonsense responsible?

thanks a bunch in advance!!

 

[Blacksheep Josh]

Whats the fluid level look like? Fill it up after you bled the brakes?

 

[dickeypjeep]

Whats the fluid level look like? Fill it up after you bled the brakes?

Yeah, filled it after each bleed. It is weird because what I took out bleeding didn't seem like the same amount I put back in (put back less). I didn't measure so who knows.

I saw a red streak in the brake fluid this morning when messing around with it. Not sure what that is...

 

[Tony H]

Red streak is probably some of the old dirty fluid rising into the reservoir. no worries.

Here's what I'm guessing; the Master was probably good until you replaced everything then had to Bleed the system. What happens is the cylinder in the master can rust in the section that the Rubber plungers never touch. But doing a complete bleeding will allow you to press the pedal to the floor causing the rubber plungers to run across the rusted part of the cylinder. This kind of screws up the seal of the plungers.
Sometime if you stop the pedal hard, the brakes will hold but if you step on the brake, not hard, it will drift down to the floor? then Master is bad.
Your GF is pretty level headed to slow it down with the E brake.

 

[dickeypjeep]

Red streak is probably some of the old dirty fluid rising into the reservoir. no worries.

Here's what I'm guessing; the Master was probably good until you replaced everything then had to Bleed the system. What happens is the cylinder in the master can rust in the section that the Rubber plungers never touch. But doing a complete bleeding will allow you to press the pedal to the floor causing the rubber plungers to run across the rusted part of the cylinder. This kind of screws up the seal of the plungers.
Sometime if you stop the pedal hard, the brakes will hold but if you step on the brake, not hard, it will drift down to the floor? then Master is bad.
Your GF is pretty level headed to slow it down with the E brake.

That is good info. I think that means that I need to just replace the master cylinder and rebleed it . I'm thinking I'll just open a bleeder on the left front wheel and keep filling the new master cylinder to flush the system out to ensure there's no more bad fluid in the system.

I was really impressed by my GF- I give her a ton of credit for just staying calm and using the e-brake. I guess she knows not to trust my mechanic skills

thanks again for the information. I'll swap the cylinder tonight!

 

[Tony H]

If you Bench bleed the new master you should not have to rebleed the lines at all.
You can Benchbleed on the car. I prefer it.
Mount the new master, keeping the brake lines off. They sell cheapo bleeder fittings and hoses that basically run the fluid from the fitting back into the reservoir until you have no air bubbles. hold the brake pedal down a little as you unscrew the bleeder and Screw in thebrakelines .
Then go to the Passenger rear and bleed a bit to clear out the old fluid.

 

[dickeypjeep]

Just reporting back- I swapped the master cylinder (bled it on the car- way easier than the bench- thanks!), and flushed out the fluid at every point on the car until it ran clean. Now the pedal is about the same, still a *little* spongy, but is consistent now, and hasn't dropped to the floor.
I'm considering it fixed!

thanks again everyone.

 

[Tony H]

Just reporting back- I swapped the master cylinder (bled it on the car- way easier than the bench- thanks!), and flushed out the fluid at every point on the car until it ran clean. Now the pedal is about the same, still a *little* spongy, but is consistent now, and hasn't dropped to the floor.
I'm considering it fixed!

thanks again everyone.

How did you bleed at the wheels? I've had great luck with a small tube coming from the Bleeder down into a jar with enough fluid in it so the end of the hose sits in it. Loosen the bleeder and have someone pump the pedal about 5 or 6 times (until you see no more bubble ) then as they hole the pedal down, tighten the bleeder. It seems to do a better job then the 'pump up the pedal, loosen the bleeder, pump up the pedal routine.
I'm glad it appears you got it squared away.

You own a Jeep?

 

[dickeypjeep]

I actually bought a 5 dollar 'one man bleeder' kit at NAPA. Its basically just what you said except is has a magnet in it so it can sit higher than the bleeder. I don't think it makes any difference but I didn't have a jar or a hose

Yeah, got a few FSJs and a CJ7 riding on 39's for rock crawling. Fun stuff!

 

[Tony H]

I actually bought a 5 dollar 'one man bleeder' kit at NAPA. Its basically just what you said except is has a magnet in it so it can sit higher than the bleeder. I don't think it makes any difference but I didn't have a jar or a hose

Yeah, got a few FSJs and a CJ7 riding on 39's for rock crawling. Fun stuff!

Love and miss the Real Jeeps Loved the J20

I have a '75 CJ5. The 'X' is just a commuter, The CJ is my fun vehicle