I am out of ideas, so I hope their is someone who has dealt with this same problem, and can fill me in on whatever I am missing. I have a 1998 GMC k1500 5.7 that I recently did a substantial amount of brake work to. The brakes where working fine, but they where beginning to show signs of their age. I had a hung front caliper, a cracked rear brake shoe, and a master cylinder that was beginning to leak. I decided that before winter hit, now was the time to do a brake job. I replaced the master cylinder, both front rubber brake lines, both front calipers, the front pads, had the rotors turned, the rear shoes, drums and brake hardware/springs ( and I did make sure to adjust the shoes out to the point I believe they are just touching the drums, and I have done multiple stops in reverse to get the adjusters going) . I was going to also do the rear wheel cylinders and the rubber line going to them, but the line was too rusty to do it without damage. Before I hooked up the master cylinder, I bench bled it as you are supposed to, and tried to be prompt as I hooked up the new lines, as to not let a bunch of fluid run out of the new master. I knew that the pedal was going to be soft because their would be air in it, but even after copious amounts of bleeding (at least 2 quarts worth), I can't get the pedal to stiffen up. The first time I tried to bleed the brakes, I tried using one of those vacuum pumps to do it by myself, but quickly gave up as I could not get a good seal on the bleeders with the adapter it came with. So after a few minutes of that I decided to do it the old fashioned way with two people. I will admit that their was one time that the reservoir ran dry while bleeding the rear brakes, but that was one pump. We have been bleeding the brakes on this truck for 4 days now trying to get a good pedal, with no success. We are not able to get any more air out of the bleeders (as far as we can tell) and still have a very soft pedal. We have even tried bleeding the ABS module, and while it seemed to send some more old fluid into the brake lines (we would see the dark fluid as we bleed them) we have not gained anything, except for maybe half a dozen bubbles at the rear bleeders. We have gone around the truck a few times now, bleeding the rear breaks, then the front brakes, in the typical order and including the ABS in with that mix of bleeding, and still cannot get any improvement in the pedal. We have even taken the truck on a few low speed drives, and ran the brakes a little bit to see if anything would change, hard and soft brake application, even getting into the ABS a little on some dirt patches. What is weird to me is 1. Before we did the brake job, the pedal was right at the top, and even with a leaking master cylinder, had a good confident pedal, and 2. Even with the spongy brakes it has right now, I can still get the tires to chirp on dry pavement, with good newer tires. So, hopefully someone can be of some advice on what I should do because I am out of ideas. Thank you.

 

Wasn’t sure from description - did you replace the rear drums or turn them?
I chased a long, soft pedal on my old 93 and finally fixed it by replacing rear drums. I assume they were too oversized and too much travel

 

@Sabino56 Sorry, the wording is a little rough. I replaced the rear drums with brand new units, and had the front rotors turned. And I did make sure to try my best to adjust the rear shoes out nice and close to the drums, and I belive the front calipers should be moveing freely as I not only replaced them, but also made sure to lubricate the bolts and where they slide on the bracket.

 

1) There’s a pintle on the combination valve that needs to remain depressed during bleeding. It meters fluid flow to the rear brakes and can allow air to be trapped inside the valve, regardless of how much time and fluid has been used.

Have a helper depress the brake pedal and look/feel for the pintle - it’s typically on the top or front of the valve, covered by a black cap. The one that extends when the pedal is pressed is the one that needs to be held down.

There’s a clip tool available for this ( ), but a penny and tape or zip ties will work if you can secure them properly.

Valve/pintle location




2) A method I’ve always used for adjusting drum brakes is to tighten up the adjuster until you can’t turn the wheel, then back off the adjuster one full turn. Then go for a short test drive (2 miles or less) and check to see if the drums are too hot - if so, back the adjuster off another 1/4 turn and repeat.

I’ve used this on several different makes and years and it’s worked every time.

 

Wow! Thanks @Gumby22 ! I couldn't find anything about that anywhere! I will definatly have to try that. Do you know anything about haveing to bleed the ABS? Their a little bleeder that is on top of the ABS motor under the hood, and we played around with that a little but it didn't seem to do much.

 

Can you post a picture? I don’t recall ever having seen one on the ABS valve but it’s been a while since I’ve had to bleed the brakes on one of these trucks.

Usually the ABS doesn’t need to be bled during normal service. It’s only supposed to be required if the hydraulic control valve has been replaced or if it’s been activated with air in the lines.

That said, I’ve run into several trucks that had a soft pedal after following proper bleeding procedure and bleeding the ABS using a scan tool corrected it.

 

@Gumby22 I think I should just share the video that lead me to think that I needed to bleed the ABS motor thing. I basically did what this guy did in his video. As I may have said before, the only thing that "changed" when we tried this is as we continued to bleed the brakes, was that some more old, dark fluid began coming out of the rear bleeders, and maybe a few new air bubbles, but very few.

 

@Gumby22 While I am thinking about it, where is that valve? Also do you bleed it like normal brake bleeders, or do you leave it open the whole time and keep pumping the brake? The way you worded it has be wondering. Thanks.

 

I also found this video

 

I forgot that some trucks were equipped with the ABS and combination valve as one assembly (may have been a design change too - I’m not sure). If that’s the case for your truck, the pintle should be the one marked by the arrow, but again, confirm that by checking for movement with the brake pedal.




The pintle needs to remain depressed throughout the whole bleeding process.

I’ll have to watch those videos later.