Hi, first posting just joined but have found info in past helpful especially current brake system issues. I have not seen answer to this specific issue.

Background. Wrong fluid in brake system. Everything has been replaced. Hard & soft lines, calipers, Used MC & hydroboost unit & ABS pump/module. Nothing brake related remains original to truck that has any seals in it.

The system has been bled multiple times before & after ABS activation. Did the redneck on jack stands ABS activation multiple times & it certainly cycled! The wheels stops on a dime In air & on ground.

What is puzzling is if after stop continue to hold the brake peddle it will sink to the floor. I'm thinking maybe still some air in hydroboost & we ran out time try check bleed it last night due darkness. But could it be the MC? Or might it just still be a little air trapped somewhere or a little leak we haven't found?

Of course with all the fluid everywhere from bleeding this thing it is hard to see if any other drips/possible leaks in system but none noted during process. It raining today & tomorrow so will probably need wait resolve.

The ABS light is off.

Any thoughts?

1999 silverado 2500 4x4 6.0 NBS

 

It going to the floor seems to suggest a blown seal in the master cylinder, You bought it used correct?

 

Yes, used. It not consistent going to floor. Somewhere read that if peddle holds firm when power off but sinks when power on that it is the booster. More ABS redneck activations. We have bled it several more times on steep hill front up & back up, & bled the hydro boost a couple more times. . Have now cleaned out the MC which had bit of dirt in it. Checked seals & looked good. Hope dirt didn't make it into my new lines. The peddle issue not as bad. It not sinking like it was. Stops good. However, it has started throwing ABS & the parking brake warning light. Goes out after turn off engine & start again. First day trip 1 hr into town no light came on. Yesterday, 4-5 hrs driving it came on at least 11 times. Haven't been able identify if any event causing it like bump, sharp turn...its come on freeway, not braking, even just sitting idling one time. I'm sure there is probably still some air in the system somewhere or debris stuck at ABS???

The ABS was used as well. Do you think symptoms of light probably just air in system or could the electronic module be iffy. I know mine was fine so could swap that out. When everything is changed at once it harder to isolate where issue is.

Knew had real solid brakes before the goof requiring system rebuild. Bummer indeed.