No brakes :(

[spddmn1]

Having a problem with the wifes brakes on her 2001 Bravada. I replaced all 4 rotors & front & rear pads, replaced right rear brake hose & caliper. No air in line & she had this problem before replacing everything listed: Driving the car & when braking the ABS kicks in on dry pavement, car very hard to stop, had both feet on brake pedal & when the car comes to almost a complete stop the brakes lock up. Was coming up to a stop sign & hit the brakes, ABS kicked in while doing 25 mph & car wouldn't stop, car slowed down & when i was at a crawl the brakes locked up & left 4 skid marks. After that the ABS light stays on. You shut off the car & restart it & the light is off. Doesn't do it all the time but enough to scare the crap out of the wife while almost rearending someone. Have a friend coming over Friday to scan the ABS. Also don't see any leaks & master cylinder is full.:bang head:

[Leeann94astro]

You need the ABS scanned, but it sounds like one of the wheel sensors has gone bad.

[old_master]

The ABS does a self test at each start up. When the vehicle is first put in motion, at about 5MPH the wheel speed sensors and ABS pump are checked. If there is a problem with the system, the ABS light is illuminated and a Diagnostic trouble code, (DTC) is set in memroy. If there are no problems, the ABS light stays off.

All 4 wheels locking up below 5MPH is normal operation, (ABS is inactive below that speed).

The low pedal when stopping is most likely due to air in the system. The system does not "recognize" air in the system as a problem, until the brakes are applied. To bleed the ABS unit, an ABS scan tool with the capability of accessing "Automatic bleed" is necessary. You might try gravity bleeding each caliper that was opened before the performing automatic bleed.

[blazee]

Originally Posted by Leeann94astro

You need the ABS scanned, but it sounds like one of the wheel sensors has gone bad.

Improper ABS activation due to inaccurate readings from the wheel speed sensors is a pretty common issue. There's a TSB about it, basically it says that you can check the front wheel speed sensors with a voltmeter. Jack the front until the tire clears the ground, set your meter to read millivolts and connect the leads to the wires coming from the speed sensor. Spin the wheel by hand at a rate of about one revolution per second, the meter should read at least 350 mv. If less, remove the sensor and clean out any debris, and retest. Repeat for the other side.

[old_master]

Chris, I think the TSB you're referring to is 02-05-25-006B. It addresses ABS activation below 5 MPH.

[blazee]

Originally Posted by old_master

Chris, I think the TSB you're referring to is 02-05-25-006B. It addresses ABS activation below 5 MPH.

The TSB addresses activation at low speeds, not just below 5MPH. I believe this is the line that you are thinking of:

"Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph)."

That's because generally people don't pay attention or recognize that they have a problem until they realize that their ABS is activating in parking lots.

[Scrapper]

Originally Posted by spddmn1

Having a problem with the wifes brakes on her 2001 Bravada. I replaced all 4 rotors & front & rear pads, replaced right rear brake hose & caliper. No air in line & she had this problem before replacing everything listed: Driving the car & when braking the ABS kicks in on dry pavement, car very hard to stop, had both feet on brake pedal & when the car comes to almost a complete stop the brakes lock up. Was coming up to a stop sign & hit the brakes, ABS kicked in while doing 25 mph & car wouldn't stop, car slowed down & when i was at a crawl the brakes locked up & left 4 skid marks. After that the ABS light stays on. You shut off the car & restart it & the light is off. Doesn't do it all the time but enough to scare the crap out of the wife while almost rearending someone. Have a friend coming over Friday to scan the ABS. Also don't see any leaks & master cylinder is full.:bang head:

if you have to push hard to stop i would think your power boosters not getting enough vacuum or booster is bad would be my first clue.

[viggy58]

yea break booster or the vacuum line to it may be leaking. one way to test is, with the car running, spray carb cleaner around the intake plenum and the vacuum connections. if there is a leak, you'll hear the idle increase as the carb cleaner is pulled in.

[Rick Norwood]

I have seen master cylinders leak back into and fill the vacuum booster up with brake fluid too. If you remove the vacuum line to the booster and carefully slide one of those fuzzy pipe cleaners into the booster, you may see brake fluid on it when you pull it out.