Brake problem- still squishy

[Paul Maurer 2]

I am trying to correct a problem my '05 has developed- about 20% of the time, my brake pedal will suddenly fail during a stop and travel to the floor as I press it, like it suddenly loses pressure in the system. The truck will still stop, but the pedal makes a strange sound and the pedal travels more than it should. I had the master cylinder replaced and the brakes bled, but it is still happening. Any ideas?

 

[Gavin Allan]

Loosing fluid level in the reservoir?

 

[Kevin Palmer]

Is the ABS light coming on?



Do you feel the pedal like kicking back at you, or just go down smooth?

 

[Paul Maurer 2]

No ABS light, fluid full and stable.

 

[James Kerr]

If you pump it when it goes loose does it build pressure again?

 

[Gavin Allan]

Sounds like another bad master cylinder. Pedal hitting the floor would have to be brake hydraulics, and no fluid loss would mean bypassing/leak inside the master cylinder. Now, if the pedal were dropping more than normal, but you still had braking ability, I would be looking at the brake booster unit as having an internal vacuum leak, etc.

 

[Larry Gamble]

Rather than start a new thread... I co-opt this one.



Anyone changed a Master Cylinder?



Left campus this morning, brake pedal went to the floor but I got some brakes at the bottom of the pedal travel. By the time I got out of traffic, I got the Check Engine Light and the brake light is on (low fluid). I haven't read the codes yet.



Fluid is almost gone. No sign of leaks at the wheels. I refilled the reservoir, it will build pressure but it dumps and the pedal sinks to the floor. And, it's loosing a bit of fluid.



I figure I've lost a seal in the master cylinder.

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[Jeremiah Morgan]

Sounds like both problems are a master cylinders!! Make sure and get the brake systems flushed!!