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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.
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.
@Gumby22 Also, I just thought of this, are you supposed to clamo that pintle down when the brake pedal is up or down? Does it matter or make a difference? Also will fluid be comeing out of it while we are bleeding the reast of the brakes? I remember when we played with it, if we tried to bleed that pinle as if it where a normal bleeder screw, fluid would come out.
The clamp (whether it’s the special tool or other method) should not be removed until the bleeding process is complete.
Inside the valve, the pintle is attached to a disc or cup (depends on design) that opens and closes against an orifice and acts as the metering valve.
When it moves (as the pedal is pressed), it creates a restriction, so the point of clamping it down is to allow the fluid to flow as freely as possible and prevent air from getting trapped inside the valve.
Minor fluid seeping is normal and shouldn’t allow air back into the system - if it’s shooting/squirting out under pressure, the valve will need to be replaced.
@Gumby22 So we tried your method of bleeding this evening and had interesting results. We just decided to have someone hold down that pintle as we bleed the brakes as normal, at first we had pushed it all the way in with a Philips screwdriver, but noticed it sounded like it was sucking air. We found that if we pushed it to where the pintle was flush with the surrounding metal, that it would still seem to push back out of its hole, as you would expect, but without sounding like it was sucking air. We got a few air bubbles out, but nothing crazy. Then we decide to put the truck back together and go for a drive and really get the ABS going. We found a long dirt road, and once we found a straight flat part, we gave the ABS a work out. I did a few panic stops from 30, 40 and even 50 MPH, and once the brakes where starting to get a little warm, we headed back home. We got back and started bleeding again, this time not touching the pintle, and a few new bubbles may have showed up, but what was most noteworthy was he color of the fluid that was coming out of the right rear bleeder (the first bleeder we started on). This fluid appears to be very old.
We continued to bleed the brakes until, once again, we stopped getting bubbles, and we continued until also got clean fluid again, just to prove to ourselves that we had bleed as much as we could. So I am still confused because even after all of this, their is very little improvement in the pedal, maybe, maybe it got a little better after the second bleed, post drive, but if so it was very minimal. So if you have any thoughts let me know. Thanks again.
The fluid is what came out of the ABS valve - it’s certainly been in there a long time.
Is it that the pedal is soft or does it just have excessive travel, meaning the brakes do seem to work fine but the pedal has to be halfway down or more before they start working?
@Gumby22 Unfortunatly I think they are soft. I was considering long travel, but when you start getting brakes, the pedal does not get hard. That leads me to belive their is still air somewhere. Any recomendations?
Inspect the lowest point of the drums where they meet the backing plates and look for signs of brake fluid leaking from there, dripping onto the rims and the tires. Any brake fluid present means the wheel cylinder(s) are leaking.
If you don’t see any fluid leaks from there, try adjusting the brake shoes all the way out - how does the pedal feel?
If it’s still soft, use hose pinching pliers or vice grips to GENTLY pinch off the rear brake hose between the frame and axle and check pedal feel again.
Repeat this process with the front brake hoses - if at some point the pedal feel improves, that’s the circuit you need to focus on bleeding.
Pinching off the hoses helps to isolate the problem circuit.
