Not usual soft brake issue.

[jiggie]

Hey all. 99 obs k1500 burban 4x4 is what were dealing with. So today while waiting in the drive through at the bbq spot i lost my brakes. Was sitting normal took my foot off the brakes to move forward pushed the pedal to stop and straight to the floor it went and the brake light on the dash came on. Nothing fixed it pumping a few times, turning off the ac nada. Got home. Backed in to the garage and boom brakes were normal and light on the dash went off. Checked the res and it was full of fluid, crawled under and checked for leaks and everything was dry. This has happened once before at a stop light but one pump of the brakes and the pedal was firm again. Any ideas what might be causing this. Pads/ shoes were new in feb along with turned rotors and new drums and brake flush.


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[edonwheels73]

Could be the brake booster.

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[east302]

Did the ABS light come on as well?

The brake light comes on when the pressure switch (located on the combination valve at the ABS unit) detects a significant difference in pressure between the front and rear brake circuits.

I'd pull the drums and see if you have a wheel cylinder leaking.

If there is no external leak in the front or rear, I'd probably look at the master cylinder, it may have an internal leak.

With the ignition off, pump the brakes five times, then slowly increase pedal pressure, seeing if the pedal falls away.


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[jiggie]

Could be the brake booster.

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When i pulled the vac hose out of the booster it made a woosh sound and i had a hard pedal. Youtube videos say that means the booster is good. Is that accurate?


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[jiggie]

Did the ABS light come on as well?

The brake light comes on when the pressure switch (located on the combination valve at the ABS unit) detects a significant difference in pressure between the front and rear brake circuits.

I'd pull the drums and see if you have a wheel cylinder leaking.

If there is no external leak in the front or rear, I'd probably look at the master cylinder, it may have an internal leak.

With the ignition off, pump the brakes five times, then slowly increase pedal pressure, seeing if the pedal falls away.


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No abs light at all. Hard as a rock after 5 pumps key off. Went for a drive to get youngest kid to sleep and had no issues. Fluid is still nice and clear. Checked my repair order from when i bought it and both rear wheel seals and cylinders were replaced in feb along with a diff service.


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[edonwheels73]

When i pulled the vac hose out of the booster it made a woosh sound and i had a hard pedal. Youtube videos say that means the booster is good. Is that accurate?


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Idk. Next time the light is on take it somewhere to read the code.

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[east302]

Could be an issue with the combination valve somehow sticking, but when the pressure switch trips those are usually a bear to get to reset. That yours resolved itself so quickly is odd. It comes on due to a large difference in pressure in the brake lines. The loss in pedal agrees with that, so you did lose pressure somewhere.

I hate throwing parts at things, but would wonder if it is some intermittent internal leak within the master cylinder.

If the ABS unit sees an issue, it is supposed to trip both brake and ABS lights, that's why I asked if that light had come on as well.




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[RED TAHOE LS]

Jonathan, with a warm engine in PARK, emergency brake OFF, get comfortable and pump the pedal twice ,mash the brake pedal firm and hold it, if you feel any movement in the pedal going towards the floor replace the m/cylinder. NEW ac Delco only. JMHO and good luck.
David g............

 

[jiggie]

Jonathan, with a warm engine in PARK, emergency brake OFF, get comfortable and pump the pedal twice ,mash the brake pedal firm and hold it, if you feel any movement in the pedal going towards the floor replace the m/cylinder. NEW ac Delco only. JMHO and good luck.
David g............[/

Ill give it a try and see what happens. Thank you fir the advise!!


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[jiggie]

Could be an issue with the combination valve somehow sticking, but when the pressure switch trips those are usually a bear to get to reset. That yours resolved itself so quickly is odd. It comes on due to a large difference in pressure in the brake lines. The loss in pedal agrees with that, so you did lose pressure somewhere.

I hate throwing parts at things, but would wonder if it is some intermittent internal leak within the master cylinder.

If the ABS unit sees an issue, it is supposed to trip both brake and ABS lights, that's why I asked if that light had come on as well.




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Got ya. Yea no abs light at all. How would i check for an internal leak? Im guessing i would need to remove the ms right?


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