Hydraulic Issue with fr. brakes.

[crownedroyal]

Hello everyone. I have a '99 suburban 1500 series, 5.7 vortec, with abs brakes, disk/drum. I'm having problems with pressure not being released from the fr. brakes after the pedal is released. I pressure slowly bleeds off after 10 - 15 minutes. I have replace both fr. flex lines and the master with OEM. Still the same problem. There appears to be no prop valve in the system, just the abs unit. If anyone has had the same problem help would be great. I tired of changin the fr. pads every 2500 miles. Thannks,

[chuck's]

Couple questions.Are you sure it is brake fluid pressure keeping the front brakes on or could it be sticky sliders or pitted caliper pistons?Do you have brake pedal freeplay?If no freeplay,the master cylinder pistons are not returning all the way and could be leaving pressure in the line.
chuck's

[crownedroyal]

Originally Posted by chuck's

Couple questions.Are you sure it is brake fluid pressure keeping the front brakes on or could it be sticky sliders or pitted caliper pistons?Do you have brake pedal freeplay?If no freeplay,the master cylinder pistons are not returning all the way and could be leaving pressure in the line.
chuck's

Yes I have replaced the sliders at the calipers. The last set of pads I installed where gm and came with new sliders. The push rod at the brake pedal is no to long. when there was pressure at the brakes I loosend the master and pulled it away from the booster and made to difference. So I don't think thats the problem. There is one thing that i should mention is that you can't push the fr. pistons in with out breaking the bleeder free. I have cracked both the steel lines at flex lines and the abs unit and when i do this time pistons move in prefectly.
If I crack the lines at the master I'm not able to move the pistons anymore. I don't know much about gm abs, is the a one way valve in the abs unit and this condition is normal?? I'm unable to see a prop valve in the system anywhere also, is it part of the abs unit? maybe it doesn't have one at all? Any help would be great I have tried everything that I can think of. Thanks. Mike.
I might add pressure is applied to both the fr. brakes its not one side or the other. And rear brakes appear to work fine. My burben has 3 chennel abs and also is 4wd.

[chuck's]

There is a possibility that the ABS unit may be faulty.I'm not very experienced on the workings of the ABS controller.Sorry.
chuck's