1996 K2500 brake pedal to the floor, bleeding issues

[Cody111]

Hey Everyone,

I replaced a blown rear brake line on my 1996 K2500. I just recently bought it from a guy who was the one who had the brakes go out on him, it had been sitting for half a year like that.

I replaced the rear line that runs from the front to back, along with the 2 rear lines on the rear axle. I then tried bleeding the normal way, cracking the bleeders while someone else is holding down the brake pedal. I have gotten a lot of air out, but now i get a solid stream of new fluid. But the pedal remains super soft, can go to the floor. I checked and bled the fronts as well. I was able to get some air out of them, but also have a solid stream of new fluid now. I have bled all the wheels multiple times and still a very soft pedal.

If I pump the pedal every 2 seconds several times in a row it will eventually get more firm. But not suitable for driving yet.

Any one have any ideas?

I have not bench bled the master, but I did bleed in on the vehicle, with no air. I also pushed the pin in on the ABS and did that trick, with only fluid coming out, no air, and no improvement.

Thanks for any advice.

 

[GrimsterGMC]

You will need to bleed the master cylinder. You will notice the front of the master cylinder is higher and the vent holes to the reservoir are at the back so air gets trapped in there. It is best to bleed it first by either loosening the bolts that hold it to the booster and tipping it forward or jacking the rear of the truck up high enough that the master cylinder is at least level, then bleed the lines.

 

[Cody111]

Thanks for the response.

So After unbolting it and tipping it forward, you would bleed the master cylinder by having someone pushing down the pedal, holding, and then cracking the lines at the master cylinder?

 

[Schurkey]

If I pump the pedal every 2 seconds several times in a row it will eventually get more firm. But not suitable for driving yet.

I have not bench bled the master,

Need to do that.

but I did bleed in on the vehicle, with no air.

Waste of time, as described previously.

I also pushed the pin in on the ABS and did that trick, with only fluid coming out, no air, and no improvement.

There is no "pin" on the ABS. There might be one on the combination valve.

You must bleed the ABS using a scan tool.

The brake hydraulic system was open for a year and a half--no telling how much moisture/contamination got inside.

After unbolting it and tipping it forward, you would bleed the master cylinder by having someone pushing down the pedal, holding, and then cracking the lines at the master cylinder?

No. And don't crack any flare nuts. Just force the front down by slightly bending the tubing.

Once it's unbolted and tipped down in front, the brake pedal isn't going to move the primary piston.

You'll have to do that with a Philips screwdriver, or a wood dowel. Don't have to move the piston very far--just "tickle" it, and the air should bubble up into the reservoir. Keep going until there's no air--just a lil' geyser of fluid in both the front and rear reservoirs.

THEN bleed the ABS. See .pdf, attached.

THEN bleed the wheel cylinders.

 

[Cody111]

@Schurkey, So you would do this bleeding procedure with the MC on the vehicle and with the 2 brakes lines still attached? Just unbolt the MC, tip it down, and gently work the piston until no air is going up into the reservoir?

 

[Schurkey]

@Schurkey, So you would do this bleeding procedure with the MC on the vehicle and with the 2 brakes lines still attached? Just unbolt the MC, tip it down, and gently work the piston until no air is going up into the reservoir?

Exactly.

An alternative is to raise the rear of the vehicle until the master has a downward slope, and then tickle the brake pedal. In many cases, the back-end has to by sky-high to get the master cylinder tipped down in front, so this isn't practical.

 

[Caman96]

Probably worth checking the front and rear hoses too.

 

[Erik the Awful]

Also, adjust your rear brakes. If they're way out, the pedal will feel spongy when in reality it's just the wheel cylinder having to take up the slack.