intermittent loss of power brakes?

[fastasleep]

I had a torn passenger front CV boot. I replaced the entire axle. Everything looks good.

I go to test drive the car and all seems fine, right up until I bring the car to a complete stop. I get this noise/vibration in the brake pedal just before coming to a complete stop, combined with a slight studdering/jerking of the car. It's like the power brakes are going in and out just before the car stops.

I know that it's a problem with the front brakes because I can e-brake the car to a stop and it never does it. I don't get this noise/vibration at any other time during the braking process - only right before the car comes to a hault; which, is why I don't think it's a warped rotor or pad not seating correctly. I would think if it were either of those issues, that I would feel it throughout the time that the car is braking; as opposed to this noise/feeling that comes on like a light switch just before I stop.

I went to test drive it again today, and was able to determine that the sound is identical to the sound that you may hear after just starting the car, where you can feel your brakes become 'power' brakes. This sound is the same sound that I get before coming to a complete stop, only accompanied by a jerking of the car and grinding/vibrating feeling in the brake pedal.

I just uninstalled and reinstalled the new axle and didn't come across anything strange. It went smoothly, and everything is back together as it was (and should be). Yet, the problem remains.

Basically, I think I can accurately describe it as: an intermittent loss of power brakes just before coming to a stop.

What would cause this?

 

[toybreaker]

Did the old c.v. shaft have a torn outer boot?

The moly gease that's in the c.v joint can get flung around a bit, and some may have gotten on the inner friction face of the rotor, and some of this grease may have transfered to the inner pad. This will give a symptom very similiar to what you are describing.

The right way to deal with this is to replace everything that was contaminated. Of course, that gets expensive quickly. You might be able to get away with a thorough cleaning, but that's your call.

Some brake clean and a blue shop towel, followed by some scuffing with a scotch brite pad will remove most of the rotor contamination. Be sure to hose it down well with brake cleaner and continue to wipe with a clean blue shop paper towel until nothing transfers to the towel.

I'm not completely sure that you can clean a pad that has been contaminated with grease.

Brake clean on a towel will get most of the surface contamination off. I would not spray the pad directly, as it will disperse the grease into the pad.

I have had some luck using rough (~ 120 grit) sandpaper on a smooth, flat surface to break the glaze off pads to allow them to reseat on a freshly turned rotor. A piece of glass, window, or the outside of a sliding glass door works well, but remember the dust is bad stuff, (asbestos or not), so be mindfull of what you're doing. I usually rinse the pad with water, and allow it to air dry.

This technique may remove enough contamination for you to determine if this is your problem.

It might be worth a try to see if it's your problem. If cleaning the rotor and pad helps, it may be time to machine the rotors, and fire in some fresh pads, in order to have complete confidence in your braking system.

I think it's very possible to have a trace level of contamination intrained in the pad, and it will boil out/come to the surface at the most inoprotune time. (like during a high speed braking event )

DON'T TAKE A CHANCE ON YOUR BRAKES WORKING!!!!!!!!!

While you're in there, please be sure to completely clean the caliper, the carrier and anything else that could allow the grease to re-contaminate the system.

 

[fastasleep]

I appreciate the response, although it was my inner boot that tore, and nothing in or around the hub assembly got near any grease.

I'm starting to think I fubar'd the ABS sensor and it's tripping out...

 

[motomattxxx]

Sounds like abs is activating because that wheel is locking before the others, this might just be because of brake pads or something though.