Pulsing brake pedal, clunking sounds, and almost dieing...

So my XJ almost killed me today.

1999 Cherokee Sport
4.0 Liter, 6 cylinder, 4x4 231 TC.

I was driving to work on a road that runs 100% straight down a mountain, has crazy turns, and has very few guard rails. (Rist Canyone Rd, Fort Collins, CO)

Aaannd my brakes died. Not completely, but if I pressed the pedal down more than an inch the brake pedal would start pulsing under my foot and lose pressure. At first I thought it was my ABS acting up, but no, my brakes were not working correctly. I had to pump the brakes all the way down the mountain and apply the hand brake on almost every turn. It was definitely one of the scariest experiences of my life. But fun too.. since I'm still alive lol.

Anyways, my brakes don't work and I need to fix them. Here are the symptoms:

- The brake pedal pulses (like its gasping for breath? its hard to describe) when I apply any real pressure.
- There is a clunking noise coming from somewhere under the car. However, It only starts making the noise when I apply the brake really hard or I exceed 35-40mph.
- thunk thunk thunk thunk thunk.

The feeling I get when I press down on the brakes is hard to describe, but its like the brakes are skipping.

I have no idea when the last time the brake pads were replaced or any work was done to the brake system. The car has about 150k miles on it. Any and all advice/comments are welcome. Also, if anyone here is from CO, a reccomendation to a good brake tech would be sweet. Thanks guys.

Buy a Haynes or Chilton's service manual and perform a brake job. At the minimum, replace the disk brake rotors and pads, and the rear brake shoes. Have the drums turned or replaced, and install a new rear brake hardware kit. You may need new soft brake lines or rebuilt calipers. You should also replace the brake fluid completely and bleed the brakes.

It does not sound like you need a brake job. I think your ABS is malfunctioning. I had similar happen on my non-XJ vehicle. First the ABS warning light came on. Then, sometimes when I hit the brakes, the pedal would start skipping under my foot and I heard grinding type noises. And the brakes would hardly stop me.

The ABS computer thinks the wheels are locking up so it modulates the pressure to the brake cylinders at the wheels. The most common reason for this is crud on the individual wheel sensors or the sensor just gone bad.

Just pull the fuse for the ABS. Then test it in a safe area. It should work fine. Then you can decide whether to chase the ABS issues or just use it with the fuse out like I have chosen to do. The dealer can put it on a computer and pull the fault codes from the ABS computer.

I don't think your brake system needs to be fully overhauled. My first thought was leaky booster- then I saw it's only a '99. Still could be the booster, just not that likely. It's somewhere on the upper end of the system (not wheels), so do that ABS-turn-off trick. If that fixes it, great you're done for now.

Leaking boosters rob the intake of vacuum air which could cause your low idle. Mine was leaking really bad- it made a loud whooshing noise whenever the motor was running. It sounded kind of like static on the radio. Then I'd have to pump the pedal to build pressure before a stop. Then it would drop idle pretty low sitting at the stop. Replacing the booster isn't that big of a deal. They go about $85, but I had to use a remanufactured one as new ones are hard to find.

So I guess check for codes, try that ABS thing, check the fluid level in your master cylinder, look for leaks all around, try to figure out if booster is bad.

HenryKrinkle said:

I don't think your brake system needs to be fully overhauled. My first thought was leaky booster- then I saw it's only a '99. Still could be the booster, just not that likely. It's somewhere on the upper end of the system (not wheels), so do that ABS-turn-off trick. If that fixes it, great you're done for now.

Leaking boosters rob the intake of vacuum air which could cause your low idle. Mine was leaking really bad- it made a loud whooshing noise whenever the motor was running. It sounded kind of like static on the radio. Then I'd have to pump the pedal to build pressure before a stop. Then it would drop idle pretty low sitting at the stop. Replacing the booster isn't that big of a deal. They go about $85, but I had to use a remanufactured one as new ones are hard to find.

So I guess check for codes, try that ABS thing, check the fluid level in your master cylinder, look for leaks all around, try to figure out if booster is bad.

Click to expand...

You seem to be thinking brake booster because of the "almost dieing" in the title. I think he was talking about HIM dying. Not the XJ motor.:explosion

1. You don't seem to have much in the way of brake skills, so don't screw around, get it to a professional technician.

2. Skip the Haynes/Chilton and purchase an FSM for your vehicle and LEARN, but don't start by trying to learn now--it is not the appropriate time.

If you are inclined to tackle the problem yourself, start by reoving the wheels and giving the entire brake system a good look-over. Look for worn pads, worn/gouged/or half missing rotors (Ive seen it before), leaks from any of the hard or flex lines front and rear, check master cylinder for fluid/leaks, and with the engine running have someone pump the brake pedal while you check the booster diaphragm for large fluctuations with a vacuum gauge. Tap into it right outside the booster.

X2!

Ground that Jeep, till its checked out and fully repaired -PERIOD!

That bad could lose all at any time. Your mountain drive was your warning - heed it.

Lets summarize: mountain road + pulsating brakes, equals warped rotor ?

The clunking could be heat induced a hard spot in the rotor, (that happened to me on the Vail pass) or an out of round drum.

Fading brakes is probably from boiling the brake fluid (mountain pass again) or glazing the pads.

A brake job is certainly not rocket science and for few dollars the OP can have the confidence that his brakes are at 100% effectiveness.


With a 99 the ABS light on the dash would indicate any ABS malfunction.

Disabling the ABS is a good diagnostic check, trouble light or not... I would do it to see what happens, on a 99 it's quite safe to do.

I also agree on boiling brake fluid, I suggest a full flush. Should be done every two years anyways and almost no one does; once water gets absorbed into the fluid it will boil and produce vapor pockets in the lines while under heavy use which makes your brakes act like they have not been bled.

Looking over the rotors/pads/everything else is a good idea too, as posted above. If there is anything you don't feel comfortable working on yourself, bring it to a mechanic... I know a few on here are from your area so they could probably recommend a trustworthy mechanic.

The ABS light is not on. I'm going to check all the basic stuff today before I commit to a mech shop.