What's This Brake Problem Sympton?

[John Haggerty]

Brothers,

Very soft brake pedal. I can pump the pedal and have good brakes. As I hold the pedal it fades to the floor. I don't see any leaks and fluid level is fine.

Probably something basic, but a new one for me.

Thanks in advance!

 

[swampdigger]

Primary seals in the master cylinder, sounds like it. It'll leak internally.

I picked up a rebuilt for less than 30 bucks!

 

[tonkadoctor]

Yup, sounds like the master cylinder is going south on ya.

 

[69oiler]

i'd pick up a master cylinder/vac booster combo. i once replaced the MC and the vac booster failed shortly after.

 

[sle2115]

I would guess the master cylinder as well.

 

[The Warden]

The master cylinder in my truck failed in the exact same manner. I replaced it, and all better.

 

[ericboutin]

Ahh me thinks master cylinder too...that's what it was when mine did the exact same thing. One thing to add though is that abs sensor (I had a shop do mine way back when so I can't remember the technical name) will probably also need to be replaced. All I know is the brakes weren't completely right until that thing was replaced also...it was a couple hundred bucks if that helps anybody name the part. Dang I can't for the life of me remember what it was called...

 

[Ironman03R]

I just wana add to make sure the rear brakes are adjusted. My truck has had a master cylinder put on it but still will slowly fade to the floor if pumped up. I was told this is normal "bypass" in the RABS valve. As long as the rears are adjusted up, I have great brakes. The pedal just sinks a bit at a stop. Its been this way since I bought it over 60,000mi ago.

 

[ericboutin]

I just wana add to make sure the rear brakes are adjusted. My truck has had a master cylinder put on it but still will slowly fade to the floor if pumped up. I was told this is normal "bypass" in the RABS valve. As long as the rears are adjusted up, I have great brakes. The pedal just sinks a bit at a stop. Its been this way since I bought it over 60,000mi ago.

RABS valve!!! That's it! That's the $200 part!! Not remembering that was driving me crazy!!

 

[Compu Doc]

Before spending a dime on a master cylinder or rabs valve

READ THIS ARTICLE IN IT'S ENTIRETY FIRST!!!

 

[icanfixall]

Check the emergancy brake. If it goes more than half way down before it works then your rear brakes are way out of adjustment. The auto adjuster rear brakes really never work correctly. After time the front brakes do all the stopping and will overheat and wear out much faster. The rotors will crack because of the extra work being asked of them. I had this sinking peddle and cracked rotors till I was told to manually adjust the rear brakes. Over time I found the "E" brake peddle came up and the brake peddle would come up after adjusting the rear brakes. Lots of thought went into this problem over time. So with this and others helping we have found by just adjusting up the rear brakes things really brake better and last longer.....

 

[swampdigger]

I adjusted my rears today as well. Being a doh-doh, I tensioned my parking brake cable (to make up for un-adjusted rears), and it over-exerted everything in the rear brakes, and stuff was out of line. Feels waaaaay nicer now.

If you have a weak vacuum pump, repeatedly pumping the brakes will make the pedal feel "firm" and it was grab much higher. If you hold it after it's firm, it will sink as the vacuum pump catches up and the power assist pulls it back toward the floor.