No Brakes - 1998 K1500 brake Pedal to the floor when running

SuitUp · May 22, 2021

Hi All,

Hoping someone here can help me because i am at a loss at this point. My brake pedal gets nice and stiff when the truck is of but as soon as i turn the truck on it goes to the floor with no to little pressure.

Here is what i have done that started this whole problem

1. replaced the rear drums and wheel cylinders.

After this i bled the brakes and messed up and let air into the front of the master cylinder resevoir (rear brake section) so i then was extremely careful not to let that happen again bled the brakes to get air out and bench bled the master cylinder. Again no air came out at the wheels, brake got stiff with truck off and then when started pedal goes to the floor.

2. I replaced the master cylinder with a brand new one and bench bled the new one and re-bled all the brakes for the 100th time and turn on the truck and again pedal goes to the floor.

I read that the power brake booster will cause the pedal to be stiff and hard to push not soft so i feel like it is working but not positive.. Also when i push the brake in the engine runs fine.. doesn't seem to want to die which i also read was a sign of a vacuum leak.

No leaks that i see anything under the truck and its been sitting in my garage while i work on it for 2 weeks so it would have been noticeable

i have read that could be the ABS that needs bled but that it requires a special scanner to do that.

Any info would be helpful if anyone has dealt with this before. EVERYTHING was working just fine before this (aside from needing rear brakes replaced) the brake pedal was working fine (for one of these old trucks at least)

Brian Lindsey · May 23, 2021

no , you dont need a scanner to bleed abs module , its more efficient if you do it that way, but it can be done with out, go to the engine bay and remove the computer nearest to firewall, dont unplug it , just move it out of way , at the rear of the abs module with be a bleeder port , bleed your abs from there , then rebleed all your brake again here is a picture of bleeder valve.

Brian Lindsey · May 23, 2021

no , you dont need a scanner to bleed abs module , its more efficient if you do it that way, but it can be done with out, go to the engine bay and remove the computer nearest to firewall, dont unplug it , just move it out of way , at the rear of the abs module with be a bleeder port , bleed your abs from there , then rebleed all your brake again here is a picture of bleeder valve.

Edited May 23, 2021 by Brian Lindsey
posted twice

SuitUp · May 23, 2021

@Brian Lindseythanks! I had actually just found this method yesterday right after posting. I probably bled that little thing about 50 times before fluid actually started coming out. (As long as the video I saw was doing it right) hold down the little pin in the middle and push brake. Finally brake fluid started coming out. But the brake still goes to floor when truck is on. Not sure how many times I should do the ABS bleed.. I bled all the brakes again and at this point pumped more than a gallon of brake fluid through it. Any idea how to know if I bled the ABS enough?

thanks for responding!

Brian Lindsey · May 23, 2021

you keep doing it as many times you need to get the air out, when that is done , then bleed wheels, the pedal will still be low ,, but not to the floor, you can check it by driving at about 25 mph and slam the brakes , they should be higher then

SuitUp · May 25, 2021

Thanks @Brian Lindsey I have read that driving and then slamming on the brakes a few places. Unfortunately i live in the city and on a hill so the initial figuring out if my brakes will stop the truck when i pull out of my garage has me a little hesitant. from all my research im leaning towards either i just suck at bleeding the brakes or air in the ABS which might need the computer to fully get out. Luckily i do have a mechanic shop just around the corner from me that i went and talked to so might just have to suck up my DIY mechanic skills on this one and get it to him to be safe and stop throwing wrenches which has become a new hobby.

I didn't think it would be the brake bleeding that would take me out after everything i have replaced on this truck haha

Brian Lindsey · May 25, 2021

when i first got my 98 , the brakes also didnt work well, it took bleeding about once a week for a month to get all the air out, then i replaced the master cylinder cause it went bad , and went though this process again, not far from my home i found a repair shop that specialized in older gm's , i took it there, and we went for a drive for about 3 miles and discussed my truck with owner of shop , and he said this is as good as your brakes are going to get,