Zumie722

Hi there. I am very lucky to have Zumie my 96 4wd 5 speed XJ. She is having major brake issues. The pedal has no resistance at all, and no stopping power in the front. Thank the jeep gods for the e-brake!! I took a look and the pads need to be replaced and rotors turned, but I am well aware that the problem is bigger than just that. Fellow Jeepers, I call upon you for guidance and some insight. Is it the booster? Master cylinder? Both? Something else? Please help me out, poor thing is sad sitting in the driveway on these hot summer days. She just wants to drive thru the creeks and get all cooled off😊💦💦💦

PatHenry

You have a hydraulic leak from the sounds of it. This could be a leaky brake line, leaking wheel cylinders/calipers or the master cylinder.

A bad brake booster usually presents itself as a heavy resistance on the pedal (in other words, you have to push very, very hard on the pedal and it's hard to push). This is not to say that the booster couldn't also be bad, but I'd start with the primary problem.

I'd start by looking for brake fluid leaking along the lines and end-points and see if it's obvious and then go from there. It's not necessarily the front that's bad, you just feel it more there since the front is something like 70% of the stopping power.

Zumie722

The fluid level is constantly full. I thought of leaky lines and calipers and checked the whole thing. All checks out. Now just before all the pressure went out of the brake pedal there was major resistance one minute and very little the next. Not long after that there was no resistance at all.

PatHenry

Sounds like classic symptoms of a bad master cylinder. If it were me, I'd replace the master cylinder, make sure it's nice and solid and then do the front pads and rotors.

Of course, if anyone wiser than myself has any additional thoughts....

Tobey

I agree. If you're not losing fluid, a bad MC is about all it could be.

GreaseMonkey17

fb97xj1

Could be the master cylinder if the seals are bad. Thats called an internal leak. When that happens, the fluid isnt being pushed thru the lines as it should. Instead, it leaks past the seals, and you lose pressure. Dirt or rust in the fluid and/or a corroded cylinder bore can damage the seals. Even if the bore was coated, they dont last forever. Doublecheck the booster for any signs of fluid leaking from the back of the master cylinder. You may or may not see anything. Sometimes it takes a while to show up. Doublecheck the rear brakes, specifically the wheel cylinder boots. They should be bone dry.

I had this happen in the Mustang once, and turned out to be the master cylinder. The seals were shot, and the cylinder bore was badly corroded. Old fluid didnt help as i found traces of rust in it.

Bugout4x4

Yep... The worn cup lips will try to flare back out against the bore for just a second and work, then they realize they are too worn to do it and allow fluid to flow by too fast. lol

Zumie722

Thank you, next step master cylinder.