Master cylinder

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Master cylinder

Postby ifixalot » Sun Jan 26, 2014 12:22 pm

I been chasing a soft, excessive travel, on my brake pedal. (1996 Z26 with 144K miles.)
I've replaced the rear slave cylinders, seemed to work for awhile. Then,
I rebuilt the master cylinder with a Doorman kit. That worked for a few days
but then the pedal goes back to soft with excessive travel again. I took the
master cylinder apart and cleaned it and reassembled again. I got some crud out
of it so I thought that was it.
It worked fine for a bout a week and now it's back to soft and excessive travel.
This always come up with the near zero cold weather and the car sits outside.
I have a power bleeder and I get all the air out so It's not that.
I've got a hunch I'm sucking air as the seals shrink in the cold.
Maybe I got a bad kit from Ebay? Maybe the kits don't work?
Or could it be related to the anti lock mechanism?
I'm thinking of trying a used master cylinder.
Anybody have this happen to them?



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Re: Master cylinder

Postby 1988GTU » Sun Jan 26, 2014 2:17 pm

check the brake booster or brake booster check valve?


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Re: Master cylinder

Postby ifixalot » Sun Jan 26, 2014 6:18 pm

Yes, while removing the hose and check valve to get the master off, I heard it suck air into the booster.
So it is holding a vacuum.
Also today, I bled the master again with the power bleeder and air came out of the bleeders and the pedal
is hard again. So somehow air is getting into the master.



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Re: Master cylinder

Postby 3X00-Modified » Mon Jan 27, 2014 9:10 am

Are you bleeding the screws on top of the ABS system too? If you don't do those then you will have air trapped up there and if the ABS clicks once it will pump the air into the system.



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Re: Master cylinder

Postby ifixalot » Mon Jan 27, 2014 11:27 am

Yes, following the GM service manual for the car, I bench bled the master, then installed it on the car. I used a pressure bleeder and bled the rear and then the front on top the ABS unit. I then loosened each feed to the wheel cylinders on the side of the ABS unit and let a little brake fluid out of those. Then onto the wheel cylinders themselves. I've put so much fluid through the system it is all fresh fluid.The pedal is fine afterward for a few days of driving. It's solid and the car stops well. Then the car sits for a day or two and we get hit with zero degree lows and I go out to drive the car and step on the brake to shift into gear and I feel the pedal go down too far, I release and step on it again and it's spongy.
I put the pressure bleeder on and I got some air out of it again.
I'm thinking the Dorman kit may be no good. It as if the seals shrink or harden in the cold, the plunger goes down through the fluid and when I release, the seal passes air instead of sucking brake fluid.
I'm deciding if I want to try buying working, used unit or try getting a rebuilt master from Autozone.
But the auto zone unit does not have an ABS attached to it.



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Re: Master cylinder

Postby 3X00-Modified » Mon Jan 27, 2014 12:53 pm

no big deal on the abs not being attached, just get the one for abs specific and you can unbolt your unit and bolt it to the new master.



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Re: Master cylinder

Postby ifixalot » Tue Jan 28, 2014 3:19 pm

Got a rebuilt unit from Oreilly's. Watch out for the gear spin when you remove the ABS from the gear plate.
Then you are supposed to rotate them ccw to take up the slack as you re-assemble. But somebody else said the gears would get back to normal eventually even if you don't
The hoses Cardone included were really stiff, maybe old stock but I got it bench bled. installed
and bled the ABS unit after jacking the back of the car up as much as I could.
Pedal feels good but the test will come as I park it outside over night again.
I bled out the air the other day and the pedal got good again but this AM as I pulled the car in the pedal was soft again.
I hope the rebuilt cylinder does the trick.



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Re: Master cylinder

Postby 1988GTU » Tue Jan 28, 2014 8:15 pm

When the pedal is firm after you bleed it, does it stop better then when it gets soft does it have a worse stopping ability?
Have you paid attention to that?


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Re: Master cylinder

Postby ifixalot » Wed Jan 29, 2014 9:07 am

When the pedal is firm, the brakes are good, when the pedal is soft, it takes longer
to stop in a panic situation. When soft, the pedal has to travel further before
the brakes engage and it feels like the power assist can't keep up with the increased travel.
So, if I were to jab on the brakes, the car will not jerk to a stop. This is why it needed to be fixed.
When I drove the other day with the soft pedal, it pulled a little to the right. I thought it was just
some rust on the rotor from not being driven. But later when a stoplight changed, I jabbed on the brakes
and the anti-lock pulsed my left front brake and I could not stop for the light and I had to go through.
Fortunately, there was no close call.
I have yet to get out to the car and see how the brakes are after another night of zero temps.



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Re: Master cylinder

Postby 3X00-Modified » Wed Jan 29, 2014 12:35 pm

Are the calipers original? You may have a bad RF caliper that is letting air into the system when it cools... maybe bad seal somewhere.

You say you get air when you re-bleed it, what location are you getting this air from? all or just one corner?



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Re: Master cylinder

Postby 1988GTU » Wed Jan 29, 2014 1:06 pm

You never went over the whip hoses and calipers as a probably suspect?

If you change out and of the calipers, I highly suggest replacing the whip hoses, if anything, at least the front two hoses.


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Re: Master cylinder

Postby ifixalot » Wed Jan 29, 2014 1:10 pm

I believe the calipers were replaced just before I bought the car. The car had a fresh brake job before I bough it.
I was getting air bubbles from the bleeders on top of the ABS unit that is how I decided it has to be the master or the ABS unit.
I checked the pedal this morning after a night of zero temps and it is still solid, thats a good sign.
I think it may have been the orings between the master and the ABS. Mine were pretty flat.
Maybe as they got cold they lose their seal and let air in.
That might explain why rebuilding the master didn't solve the problem.



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Re: Master cylinder

Postby 3X00-Modified » Wed Jan 29, 2014 1:29 pm

Never re-use o-rings in a case like that... That's why I went and bought a few big bins of them so I almost always have a choice to replace them.



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Re: Master cylinder

Postby ifixalot » Fri Feb 07, 2014 1:01 pm

SSDD
So I go out after a couple days and it's near zero again,
going to drive to Home Depot and the pedal is soft again.
Not quite as bad but more travel and softer than normal. I hate driving this way.
On my way back, going down our snow covered street, I hit the
brakes just kinda playing around, the anti locks kick in and after the pedal is back up again.
This is strange. The pedal got soft when I hadn't even moved the car yet.
Maybe I should have gotten the use master with anti-lock unit.
The saga continues.



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Re: Master cylinder

Postby Money pit Beretta » Fri Feb 07, 2014 1:20 pm

Did you replace the soft lines up front? Are you bleeding like you would when rotating tires/wheels?
I swear up and down that the booster is the problem. If it was warm out I could tell you. My new Delco one is just wating to go on.
As a side note I replaced everything on my 90GT but the booster and still had a very soft pedal.

Damn boosters have alot more parts in there than you would think.


keep'em flying!


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