Brake issues...

[Hathorite]

Hello everyone. I'm trying to fix a '98 explorer for my in-laws. They brought it to me saying the brake pedal went to the floor. Said it was braking fine and all of a sudden it just went to the floor. I checked for leaks and there were none. Pulled the rear wheels off and the pads were non-existent. Replaced those and still no pedal. Bled the master cylinder with the bleeder valve on the side, and bled the rest of the system, starting at the pass rear. Still nothing. Any suggestions? Could it be the master cylinder? On a budget because Michigan's economy blows right now and want to be sure it is bad before throwing parts at it.

Thanks,
Bryan

 

[marragtop]

Was the master cylinder every dry, and is the brake light on? If the cyl wasn't dry, it sounds like a bad master cyl. Also, make sure that the line across the rear axel isn't leaking. Keep in mind that a fluid leak can come from more than just a wheel.

 

[Hathorite]

1

 

[Hathorite]

Sorry. I forgot to mention I had already traced the lines and they were fine. No lights are on. As far as I know the MC was never dry. I pulled the MC off and opened it up. All the seals look fine. Bled it at the lines and bleed valve, then all the wheels again and nothing.

 

[Dan Whitaker]

Just throwing this out, but could it be a bad brake booster?

 

[Hathorite]

If it was the booster, wouldn't it cause the peddle to be harder? Nonetheless, how would I test it?

 

[Dan Whitaker]

The booster relies on vacuum to operate. It's possible there is an internal leak in the booster causing the pedal to go the floor.

You could check this by hooking a vacuum tester to the booster and see if it holds or bleeds off.

 

[Hathorite]

That would make sense seeing as the pedal is firm when the engine is off, disappears as soon as the engine is started. I'll have to go and pick up a vacuum tester tomorrow. I'll keep everyone posted on the results. Thanks for the replies.

 

[pservecc]

I have a related question... My pedal is spongy whenever the engine is running, but when it's off, a couple of pumps will firm it up nicely. The first one does go down to the floor, however. Is that indicative of air trapped in something, or worse?

 

[NHale623]

I have a related question... My pedal is spongy whenever the engine is running, but when it's off, a couple of pumps will firm it up nicely. The first one does go down to the floor, however. Is that indicative of air trapped in something, or worse?

Yes. A spongy pedal is an indication of air in the brake lines.

 

[Hathorite]

Well I picked up a vacuum tester and hooked it up to the booster. Couldn't even get a reading. I then disconnected the vacuum line from the engine and plugged it and the pedal stiffened right up. Spongy, but another bleed should take care of that. Thanks everyone.