I finished installing a C5 front and an LS1 rear brake kit on my car, and now I am sometimes having the problem where I will be slowing down and the brake pedal will go almost all the way to the floor. It doesn't want to stop so I will have to let off and try braking again. However after it does this, it may not even do it again for a few days. What could be causing this?

 

I had that problem once. Ended up being a bad master cylinder.

 

Could something have possibly happened to the master cylinder when I bench bled it?

 

Possibly. Maybe start looking for small leaks.

 

Or, as cheeeep as those are, just change it out and be done with it.

Life is already too short; no sense making it even shorter over a defective $15 master cyl.

 

mine just started doing that today...I was slowing pulling out of my apartment complex & noticed my brake pedal went all the way to the floor & didnt stop so I let off & pressed on my brakes again & it stopped. As I drive down the street if I pump my brakes it stops great.

 

I have a c5/ls1 set up as well, I lost all of my fluid one day and had to bleed the master and whole system. Now I have the same issue as you two, and I'm 99% certain it's the master, because from what I have read boosters either work of they don't, they are not a "sometimes it doesn't work" item and everything else in the brake system is real simple, so it's gotta be the master.

I've heard when bleeding the master you push the seals further than they normally go and they can hit deposits/dirt that have been left behind after years of use, and It will ruin the seals causing the issues we are experiencing. Like sofakingdom said, masters are cheaper than a wreck/injury, they are old anyway so replacing them is not a bad idea anyways. If either of you do replace the master and it fixes the issue, please post up!

 

If it was the booster the pedal would be hard, like when the car is off and you step on the pedal a few times. You either have a massive leak, or the master is bad.

 

I don't have any leaks & I'm sure it isn't my brake booster so I will definitely be changing my master cylinder tomorrow after work. Good thing my Iroc isn't my DD.

 

so it was the master cylinder! changed it out & now my Iroc is braking great! Just a quick tip: BENCH BLEED, BENCH BLEED, BENCH BLEED! Makes installation way easier...