Brake Issue

[97C1500TJ]

So I rebuilt my master cylinder with a Raybestos rebuild kit and got no fluid out of the front hole on the bench bleed. This left me stranded for a few days. Then I get a new master cylinder, bench bleed it, and bleed my brakes in the dark. I keep getting air out of my right rear bleeder. It doesn’t seem to be getting any better or worse. All of the other bleeders cleared up. I’m aware of the order to bleed but I was trying the others too. My brake pedal goes to the floor still. I’m not sure what to do.

 

[Schurkey]

HOW are you bleeding the right rear brake? How are you bleeding the ABS?

If you're vacuum-bleeding, it's no surprise that you get air indications.

As for the pedal going to the floor, I bet there's still air trapped in the master cylinder and/or the ABS.

 

[Gibson]

All of the other bleeders cleared up.

That's not a guaranty of a solid system, air can still be in the ABS module.
Using a scan tool to cycle the ABS along with pressure bleeding is the best way to proceed.

 

[Pinger]

Does anyone know exactly what the two 'things' on the ABS unit with pintles on them are and are for?
Two of them on opposite sides (one points inward to the engine bay, the other outward) held in with a largish nut each. They are adjacent (I think) with the two pipes that come from the master cylinder and possibly communicate with the ports each of those pipes are screwed into. The pintles can be pushed in but on mine they are already in unless there's pressure on the brake pedal.

 

[97C1500TJ]

I’m bleeding with someone at the pedal and someone at the bleeder valve. Is there a way to bleed the MC on the truck? I bleed right rear, left rear, front right, and finally front right.

 

[Pinger]

I’m bleeding with someone at the pedal and someone at the bleeder valve. Is there a way to bleed the MC on the truck? I bleed right rear, left rear, front right, and finally front right.

I'm curious about this too. Not least because between bench bleeding and fitting there is the possibility of air entering before the connections are made.

In theory the same as bench bleeding could be done in situ via the pedal with the brake pipes disconnected.

Still want to know more about those nippley things on the ABS unit. Definitely they've been referred to as for bleeding on this forum before now.

 

[delta_p]

Does anyone know exactly what the two 'things' on the ABS unit with pintles on them are and are for?
Two of them on opposite sides (one points inward to the engine bay, the other outward) held in with a largish nut each. They are adjacent (I think) with the two pipes that come from the master cylinder and possibly communicate with the ports each of those pipes are screwed into. The pintles can be pushed in but on mine they are already in unless there's pressure on the brake pedal.

Those are the ends of the valves inside the combination valve (bolted onto the BPMV/ ABS package) for rear proportioning and front metering.

 

[Pinger]

Those are the ends of the valves inside the combination valve (bolted onto the BPMV/ ABS package) for rear proportioning and front metering.

Found this >> https://www.gmt400.com/threads/brake-bleeding-w-rear-abs.41894/

Without anyone to press on the pedal I have held the pedal down with a stick and poked at the valve - should fluid come out?
I've once seen a small spurt of fluid from it but only once. Cant tell if air is being expelled but when I go back to the pedal it seems to be as it was - ie, not lost travel. I've only dicked about with the driver side one - not the other one. Maybe time I did?

 

[Schurkey]

IIs there a way to bleed the MC on the truck?

I'm curious about this too. Not least because between bench bleeding and fitting there is the possibility of air entering before the connections are made.

In theory the same as bench bleeding could be done in situ via the pedal with the brake pipes disconnected.

You need to bench-bleed, because there's a LOT of air to be removed. Once the majority of air is gone via the usual method, on-the-vehicle bleeding is recommended.

Leave the brake tube(s) CONNECTED. Most masters are installed with the front tipped "up" when the vehicle is level. Air rises--to the WRONG END of the master cylinder to bleed out.

Lift the rear of the vehicle so the front of the master cylinder is tipped "down". "Tickle" the brake pedal so that you apply the primary piston just a little bit.

OR

Unbolt the master from the firewall or booster, push the front of the master "down" by gently bending the tubes. "Tickle" the primary piston with a wood dowel or Philips screwdriver.

Either way, tap on the master with a brass hammer, or any other metal tool to encourage air bubbles to rise to the rear of the cylinder.

You should see air bubble into the reservoir as the piston is tickled. Continue until there's no more air bubbles. You are NOT pushing very far on that piston--1/4" or so should be enough. It may be that the primary piston area will bleed before the secondary.

 

[delta_p]

Found this >> https://www.gmt400.com/threads/brake-bleeding-w-rear-abs.41894/

Without anyone to press on the pedal I have held the pedal down with a stick and poked at the valve - should fluid come out?
I've once seen a small spurt of fluid from it but only once. Cant tell if air is being expelled but when I go back to the pedal it seems to be as it was - ie, not lost travel. I've only dicked about with the driver side one - not the other one. Maybe time I did?

The only one you might have to hold in is the front metering and only if pressure bleeding. I believe it is like a single but two stage valve. One that closes from around 25-100 psi, and then it opens up from 100 psi on. If you are not changing out the combination valve or an ABS pack you should not have to bleed any of that. The ABS is not in the brake system under normal operation because its valves are closed. It's just a pass through with all its components isolated.

I usually just bench bleed the master if i am changing it and install it. then hold the pedal down and crack the tube fittings at the master and tighten it, then go let up the pedal. Always worked for me. If bleeding brakes I just use the old push the pedal, crack the bleeders, tighten, and let up the pedal.