Brake Issue
 

Hey guys, So Ive been doing research and have been unable to understand what the issue is or where to start looking, So here's the history.
I replaced a caliper quite some time ago.
I bled the new caliper and line going to it.
some time after i had issues where my master cylinder was going all the way to the floor and i had no brakes. I replaced that. the issue went away for a while. Then came back, I took it into the shop and they replaced the booster again, bled the whole system out and so on.
Now occasionally on start up or lower RPMs i can put the brake right to the floor and nothing.
Once the rpms are up its good.
I'm thinking vacuum issue but not sure where to start.
Any help would be nice.
Thanks

Sounds like a vacuum issue to me as well! Start by checking all of the vacuum lines on the entire truck for cracks or any other sign of damage. Also make sure your vacuum accumulator ball/box is in good shape with no damage.

Sounds good, Would water in the vacuum reservoir cause these issues at all? i had issues with my first gen when i got it wet the cruise would act up, found water was getting into the ball.

Did you get a rebuilt master cylinder? You may have gotten a bum unit. I've seen boosters do this but it's pretty rare. I've seen more master cylinders that got bad seals just do this on odd occasions. As they fail, they will do it more and more then all the time.

The master that the shop put in was brand new. Funny thing is that it appears to only occur during low rpms. Im getting new lines and check valves this weekend

Sounds like air trapped somewhere. I don't see anything about doing the automated bleed. Your 05 has ABS and when the master cylinder is replaced, it introduces air into the EBCM. The bleed MUST be done to expel the air from the solenoids. Using a scan tool capable of initiating it is the only way to expel the air into the lines. After the automated bleed, each wheel must be bled to remove the air from the lines.

This was done at the shop i did some extensive reading and ensured it was done when they changed out the master

Seems as though the problems started when you replaced the caliper and bled it out. Did you gravity bleed the caliper and line after replacing the caliper, or did you pump the pedal to bleed it?

+1 to Captain. i would say its a combination of both vacuum leak and improper bleeding. and why did you just change the one caliper? i have always been told (at least with brakes) what you do to one side is what you do to the other. so if one caliper failed, you would change both on that axle. if the hose failed, change both on that axle. like i said, this is what i have always been told.

the other possibility is that your booster is bad. i have seen them bad out of the box. it is a real pain in the butt when that happens too! i would start with vacuum lines and you and a buddy rebleed the brakes. all of them, starting with the passenger rear, then driver rear, the front passenger, then driver front. see where you are then. it will only cost you brake fluid and maybe someones lunch.

just my .02

I did gravity bleed the entire system twice to flush out all the crap in it.
As well the shop bled the entire system. I dont think it is the brake booster because it was fine. I got parts ordered to replace all the rotten vacuum hoses as well as new check valves and seals. Ill fill you all in after im done with it