[larry1]

Has anyone ever heard of this? The abs system slowly applying force to the brakes without me stepping on the pedal. I just get out and let the pressure off by opening one of the bleed valves on any wheel and this solves the problem for a little while, 10 miles or so depending on how much I use the brakes, yet It keeps coming back. Even happened going down the freeway without using the brakes at all. Recently changed a master cyl. and did get air into the system but I bled them and even fliped the front calipers in front to make sure there wasn't air in them. The abs light is on in the instr. cluster so I will have to have the dealer put the abs system in bleed mode but in the meantime if anyone has dealt with this or has any ideas what the #$%^ is going on give a shout. Thanks larry

 

[ChrisH]

The master cylinder is supposed to release the pressure in the braking system when you let off the pedal, not the ABS. The ABS can release pressure while you are braking, not apply it. It sounds to me like your new master cylinder is deffective and allowing the vacuum booster to slowly engage when it shouldn't (maybe a valve to the vacuum booster not fully closing - I think that vacuum valve mechanism is in the master cylinder, but I could be wrong as I didn't look it up recently).

 

[larry1]

The master cylinder is supposed to release the pressure in the braking system when you let off the pedal, not the ABS. The ABS can release pressure while you are braking, not apply it. It sounds to me like your new master cylinder is deffective and allowing the vacuum booster to slowly engage when it shouldn't (maybe a valve to the vacuum booster not fully closing - I think that vacuum valve mechanism is in the master cylinder, but I could be wrong as I didn't look it up recently).

Thanks chris, I pulled the abs fuse this evening and it still did it. I'm gonna change the booster(got an extra) tomorrow and see if we developed a problem there. Still gotta have the abs bled, stomped on brakes today to activate the abs and succeded in locking the front wheels, not the rears:crazyeyes so obviosly there is air screwing up stuff.

 

[R T]

Sounds like maybe the pedal is adjusted to engage way too soon so it is slightly actuating the master cylinder (not letting the system pressure completely bleed back to the reservoir).

 

[Dragon]

Sounds like maybe the pedal is adjusted to engage way too soon so it is slightly actuating the master cylinder (not letting the system pressure completely bleed back to the reservoir).

+1

There should be a little bit of play in the adjustment rod... If it's tight then the piston will not return to the rear position and allow the pressure back in the reservoir... Simple and easy to do except for the part where you have to maneuver your body on to the floor and reach up under the pedals...

 

[spectre]

My abs was kicking on the front (left front actually) turned out to be the sensor and the main abs computer. Both replaced and has been perfect since.

 

[karajabola]

If you feel the need, you can disable the ABS controller by disconnecting a front wheel speed sensor (there should be a 2-pin connector somewhere around the suspension bits) Note, in this scenario, you may still have DRP enabled (Dynamic Rear Proportioning, a function performed by the controller that replaced the need for prop valves not too long ago) If you want to disable DRP, you'll want to disconnect a rear wheel speed sensor also.

Disclaimer: DRP is a safety feature to prevent rear wheel lockup, I'd avoid disabling it if you can.

 

[Dragon]

If you feel the need, you can disable the ABS controller by disconnecting a front wheel speed sensor (there should be a 2-pin connector somewhere around the suspension bits) Note, in this scenario, you may still have DRP enabled (Dynamic Rear Proportioning, a function performed by the controller that replaced the need for prop valves not too long ago) If you want to disable DRP, you'll want to disconnect a rear wheel speed sensor also.

Disclaimer: DRP is a safety feature to prevent rear wheel lockup, I'd avoid disabling it if you can.

This will also more than likely disable or cause issues with traction control as well if you have it installed since they also rely on the wheel speed sensors.

 

[larry1]

Has anyone ever heard of this? The abs system slowly applying force to the brakes without me stepping on the pedal. I just get out and let the pressure off by opening one of the bleed valves on any wheel and this solves the problem for a little while, 10 miles or so depending on how much I use the brakes, yet It keeps coming back. Even happened going down the freeway without using the brakes at all. Recently changed a master cyl. and did get air into the system but I bled them and even fliped the front calipers in front to make sure there wasn't air in them. The abs light is on in the instr. cluster so I will have to have the dealer put the abs system in bleed mode but in the meantime if anyone has dealt with this or has any ideas what the #$%^ is going on give a shout. Thanks larry

Well I located the problem, kinda, the @#$# booster kept applying pressure. I'm not sure if there is a pressure reg. in the back, prob. the same thing as people are experiencing in ice mode just too much pressure versus not enough(anyone wanna trade sensors). I'll let you know what comes up. Maybe help the people with ice mode prolems.