Need help with brake bleed problem

[BonesDT]

The frame rubbed a hole in the front master brake line so I replaced it. No ABS.

I used a Motive Power Bleeder and bled the right rear wheel then the left rear wheel. I was surprised to see not a lot of air bubbles, if barely any at all, and I bled them until the new clear fluid came thru.

I had Speed Bleeders on the front calipers from before I bought the Motive, and I found out that the Motive at 16 psi wasn't strong enough to push thru the SBs, so I removed the Motive and bled the fronts using the SB feature.

I then turned on the truck and the pedal went to the floor. I rebled everything like above and still went to the floor. I then realized I could pump the brake pedal (engine off - all bleeders closed) to the floor about 3 times, and the master cylinder reservoir would bubble up for a few seconds. I kept doing this and it was like an endless supply of air coming out from the master cylinder.

When the Motive was hooked up, it showed no signs of a leak (would maintain 15psi). No dripping fluid anywhere.

I didn't bleed the Master first because it would have been a pain in the ass to remove and do that. I've bench bled the Master before, and I felt like it was more work than as necessary. I especially don't see the reason to bench bleed at all when you have a Motive and a large bottle of brake fluid.

Recommendations?

 

[Rick]

Sounds like you may need to bleed the master separately then go back and bleed the brakes. If that doesn't work, the M/C may have went bad from the piston going to far in the bore. What can happen is that the piston wears out a small length of the bore and when you let the pedal go all the way to the floor, the piston ends up pushing past an unused area of the bore and the piston gets scored which causes an internal leak.

 

[BonesDT]

I think you might be right about the MC being blown. I replaced it recently, but the infinite bubbling over when I pump the brakes could only be indicative of an internal leak in the MC.

I might have another issue going on. Has anyone had experience with a Metering Valve aka Hold Off Valve, which is part of the Combination Valve? Below is a diagram of a combo valve similar to mine.

Suprisingly, there is very little info about this online, but it is in a lot of cars. The Metering Valve cuts off all brake pressure to the front disc brakes when the hydraulic brake pressure is between about 3psi and 149psi. What this does is, as soon as you touch the brake pedal, it gives the rear drums a head start to set the springs before the front discs kick in at 149 psi (a relatively low pressure when trying to slow down a car).

This poses an issue with bleeding. If you gravity bleed (0psi) or traditional 2-person pedal bleed (>149psi), fluid will flow fine to the front brakes; however if you use a Motive Pressure or a Vacuum Bleeder (between 20-30psi), you fall within the lock out range and fluid won't flow to the front brakes out the bleeders.

Now, what I'm suppose to do is either push or pull (never found an answer to that) that nipple on the left of the diagramn to release the block off. I tried both and I can't budge that nipple. Is it suppose to be easy to move? Could mine be seized up?

 

[BonesDT]

Thanks Rick, it was the MC. Got a $25 reman.

Funny thing, went for a little test drive, turns out I have ABS. I could of sworn I didn't have ABS, and I was having a good time laughing at the dumbness of my insurance company giving me the ABS discount.

That Hold-Off Valve pin was rusted still. I gave it some wire brush, penetrating lube, and hammer love and got it mobile. Before, I would slam on the brakes and the rear would lock up and slide everywhere, I just blamed it on 1989 pickup technology. Now, my brakes are better than ever, and I went out trying to break the rear loose and I couldn't and the pedal starting pumping from the ABS!


Cool.