Problem with brakes on 96 k1500

[beastybaconman]

There's something up with the brakes on my truck and I can't seem to figure out what the problem is. When the truck isn't running the brakes pump up and feel pretty solid but when it's running they're pretty soft. And while it's running, if you don't pump the brakes and just slam on them the brake light on the dash comes on and stays on until you tap the pedal again. I had to replace my front calipers because they were all rusted and nasty, and I also replaced the master cylinder because when I hit the brakes bubbles would come up from the bottom of the reservoir and I figured the seals were bad. The brakes were soft before I replaced everything and I've tried bleeding them multiple times since replacing everything, but they aren't getting any better. The only thing I haven't messed with is the abs, and I'm not sure how I'd get air out of there anyway. If anyone has any idea what the problem could be I'd appreciate some advice.

 

[21Actual]

Did you bench bleed the master before installation? And did you bleed all 4 corners after the master replacement? If yes to both, (assume you dont have access to a high end scanner with advanced functions) go find a gravel road and get on the brakes hard enough for the abs pump to cycle. Do this a couple times, then bleed all 4 corners again. Repeat if necessary.

These trucks can be a bit tedious to get air out of the brake lines.

Keep in mind that the brake pedal feel and the brakes themselves on these trucks leave alot to be desired.

A GMT800 master, properly adjusted rear brakes and some stainless braided flex lines makes a world of difference.

 

[beastybaconman]

Did you bench bleed the master before installation? And did you bleed all 4 corners after the master replacement? If yes to both, (assume you dont have access to a high end scanner with advanced functions) go find a gravel road and get on the brakes hard enough for the abs pump to cycle. Do this a couple times, then bleed all 4 corners again. Repeat if necessary.

These trucks can be a bit tedious to get air out of the brake lines.

Keep in mind that the brake pedal feel and the brakes themselves on these trucks leave alot to be desired.

A GMT800 master, properly adjusted rear brakes and some stainless braided flex lines makes a world of difference.

Yeah I did bleed the master cylinder before I put it on, and I bled all four corners a couple times after it was on. I don't have a scanner though so I'll try that dirt road trick tomorrow and see what happens.

 

[east302]

Have you checked the drums? Are they adjusted? How does your parking brake pedal feel?


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[Ironhead]

I just went through all this as I had a spongy pedal and dirty fluid. I sucked all the dirty fluid out of the reservoir, re-filled with fresh, then forced the ABS to cycle several times on snowy/icy roads. After that, I bled all four corners with a Mityvac, and the pedal is very firm now.

There's a Youtube on using a vacuum pump to bleed the brakes if you have access to such a pump.

 

[beastybaconman]

I took it down a dirt road and got the abs to run, but after bleeding all four corners it didn't make a difference, I might just need to do it a couple more times, maybe with some kind of pump like ironhead said. Something weird happened when we tried bleeding them though, I pumped up the brakes and my dad opened the bleeder but the pedal only went down half way to the floor. It only happened when we bled the rear brakes, the front ones bled like normal, any idea what could've caused that?