Jimmy - Brakes (Please Help!)

[danfman]

Sometimes when my 1998 GMC Jimmy is decelerating at speeds between 7-2 miles an hour I can hear a noise almost like a cow's moo. There is no pulsating or other problems when brakes are applied at higher speeds. The noise doesn't come every time, but probably most. When I hear the noise and if I try the brakes they don't work properly. The peddle is real stiff and braking is very hard. Then without warning the noise goes away and the brakes work fine. I've had mechanics already replace the pads, rotors, flexible brake hose, and front left caliper. None of these helped. No one seems to know what is going on. Sometimes when my 1998 GMC Jimmy is decelerating at speeds between 7-2 miles an hour I can hear a noise almost like a cow's moo. The noise doesn't come every time, but probably most. When I hear the noise and if I try the brakes they don't work properly. The peddle is real stiff and braking is very hard. Then without warning the noise goes away and the brakes work fine. I've had mechanics already replace the pads, rotors, flexible brake hose, and front left caliper. None of these helped. No one seems to know what is going on.

[ChrisGood]

Looks like you hit that paste button one too many times, anyway no expert but there are only a couple things left, one being the master cylinder.....

[danfman]

I did a little more investigating last night. I unplugged the ABS fuse and the system started working fine. Does anyone know if it's possible to get an accurate scan even if the ABS fault light isn't on? How else would I determine the problem with the ABS?

[drdd]

how about the brake booster? you got any small vacuum leaks? that would cause tough braking. you got a cow stuck in there? that would cause it too.

Originally Posted by danfman

I did a little more investigating last night. I unplugged the ABS fuse and the system started working fine. Does anyone know if it's possible to get an accurate scan even if the ABS fault light isn't on? How else would I determine the problem with the ABS?

[adamdinat]

Originally Posted by danfman

I did a little more investigating last night. I unplugged the ABS fuse and the system started working fine. Does anyone know if it's possible to get an accurate scan even if the ABS fault light isn't on? How else would I determine the problem with the ABS?

I had this problem on my 2000. The ABS would engage on low speed stops with a mooing or groaning sound. You could feel it in the pedal. I believe the dealer replaced the ABS sensors.