Brakes seem to have gotten soft (1 Viewer)

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SteveNJ

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Was out wheeling a couple weekends ago and suddenly op while holding on a hill, slightly off camber the brake pedal started to sink. The truck still held and still stops even now, but it is crazy soft, like to the floor. I do feel it gradually start to brake even with just a little pedal effort but full stop goes all the way down.
Pump the brakes, they get firm and then pedal starts to sink as it is held.
Before this they were passable, new caliper, some hard lines, replaced rubber lines, new pads, new LSPV all over the past year or so.
Everything was fine until that one day, it does not leak, fluid level has been the same since before the problem. Full system has been bled a few times before this, not since.

Is it a dead MC?
 
When you apply the brakes at idle, if the engine idle/rpm's change or if you hear a woosh sound coming from the pedal area then your brake booster has gone bad.
 
Classic symptoms of a bad master cylinder. Something to be aware of if you replace it is that a lot of new master cylinders are bad right out of the box.
 
Cool, thanks for confirming my thoughts. The bad MC's are Toyota parts or part store?
 
The bad MCs are mainly parts store, although I've heard of Toyota ones as well. The big problem with the bad MCs is that people replace the MC and still have brake problems and start replacing brake booster, flex lines, ABS components, etc. when the MC is the problem.
 
I just replaced my MC (OEM), and not but a few weeks later, booster is dead. So now I get to go in and do THAT job.

There's some merit to "while you're in there" replacing the booster if it's original. Then again, it's not a cheap part. But neither is the MC either!
 
Be careful as you are just braking on one axle with the bad mc. The boosters go out as they're already old and driving with a bad mc strokes the booster diaphragm to the end of it's travel at every stop-probably rupturing the 20 year old rubber that had never been stroked to it's limit.
 
Hmm may just do both then while I'm there, already did pretty much the whole rest of the system
 

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