Why doesnt my brakes bleed properly?

Tiny
BOBSTUCK
  • 1986 PONTIAC 6000
  • 135,000 MILES

I have a 1986 pontiac 6000. The master cylinder has four ports (2 with proportioning valves). I changed the m/cyl and tryed to bleed the brakes. Only one front and one rear would bleed. The other 2 would not let the pedal depress down thus reducing stoping. The pedal is hard to depress and the vacuum booster is good. Help.

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Thursday, September 20th, 2012 AT 12:23 AM

13 Replies

Tiny
SATURNTECH9
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Did you bleed the master before hooking all the lines up?

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Thursday, September 20th, 2012 AT 12:30 AM
Tiny
BOBSTUCK
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Yes. I was told to plug the two ports with the proportioning valves then bleed the two top ports.

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Thursday, September 20th, 2012 AT 12:37 AM
Tiny
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Thats how you bleed the master?

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Thursday, September 20th, 2012 AT 1:00 AM
Tiny
BOBSTUCK
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I master was bleed properly could it be a bad master cyl?

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Thursday, September 20th, 2012 AT 1:16 AM
Tiny
SATURNTECH9
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Did you bleed the master back into itself with hoses till there wasnt anymore air left?Also why did you replace the master?

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Thursday, September 20th, 2012 AT 1:35 AM
Tiny
BOBSTUCK
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Yes. I replaced it because the pedel was slowly going to floor. Then out I had a leaky front hose. Should I rebleed the master?

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Thursday, September 20th, 2012 AT 5:09 PM
Tiny
SATURNTECH9
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I would did the new master come with a bleed kit?

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Thursday, September 20th, 2012 AT 5:26 PM
Tiny
BOBSTUCK
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Yes

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Thursday, September 20th, 2012 AT 5:35 PM
Tiny
SATURNTECH9
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Did you use the kit to bench bleed it before hooking the lines up to the car?

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Thursday, September 20th, 2012 AT 7:34 PM
Tiny
BOBSTUCK
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Lets start over. I bleed the master cyl using the kit provided. The instructings said to plug the lower ports with the proportioning valves and use the hoses o;n the upper ports. In which after doing I located a leaking front hose. Shoud I have rebleed the master cylinder?

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Thursday, September 20th, 2012 AT 8:55 PM
Tiny
CARADIODOC
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Hi guys. Excuse me for jumping in here but there's a real easy solution.

On GM vehicles with the step bore master cylinder, imagine a teeter totter that is level, but if it moves one way, it will block the ports for two wheels. The teeter totter moves when one hydraulic circuit builds pressure and the other one doesn't due to a leak or from pedal-bleeding the system. As soon as the pedal is pressed while a bleeder screw is open, the teeter totter moves to block the ports for one front brake and the opposite rear brake. No fluid can be forced out of those two bleeders.

If the system is left like this, one front brake will wear out very quickly and the other side will look like new. People usually ask for advice when they run into worn pads on one wheel for the second or third time. The car will usually not have a brake pull because alignment angles are modified to accommodate loss of one hydraulic circuit on the split-diagonal systems.

The only way I ever found to reset the valve in the master cylinder, (that teeter totter), was to give a quick, short burst of compressed air to one of the bleeder screws that isn't flowing. Don't use so much air that it makes its way up to the master cylinder. A fraction of a second is sufficient. After that, just let it gravity bleed.

The same problem can happen even when the hydraulic system wasn't opened. After installing new front pads, the pistons must be worked out until the pads contact the rotors. One piston will always move first, then, once contact is made with the rotor, pressure will start to build up. That will trip the valve at which point the other piston will never move. Once the burst of air is given and the line gravity bleeds, pressing the pedal no more than half way to the floor will prevent the valve from tripping again.

This same master cylinder can be used with the factory "add-on" ABS system that is bolted directly to the ports of the master cylinder.

Even with normal master cylinders, you should never press the brake pedal more than half way to the floor when pedal bleeding. The lip seals will be torn on the debris and corrosion that build up in the lower half of the bores where they don't normally travel.

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Thursday, September 20th, 2012 AT 9:11 PM
Tiny
BOBSTUCK
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Thanks for the help. It was teeter totter valve.

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Saturday, September 22nd, 2012 AT 7:52 PM
Tiny
CARADIODOC
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All right! One in a row.

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Saturday, September 22nd, 2012 AT 8:14 PM

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