Hello all, its been a while since I posted here, but Im hoping you guys can help.......Camp trip next week end is in danger.....

2008 4x Big horn (49K on the clock)- all things normal, no issues when I parked it in the garage. Backed the truck up out of the garage the next morning, wth....no/very little brakes. Pedal goes half way to floor and gets very hard. No Brake light or abs on cluster, nothing.

Checked the fluid level, no issues. Removed wheels, pads had 1/4 life on them. No fluid leaks, hoses all in good shape. Decided to replace the pads.

All put back together, same issue.......engine off, pump the pedal, goes 1/4 travel get hard. engine on, pedal goes half way with relative little pressure applied to pedal then very hard to go any further at half way point.

Drove the truck up the street, at idle, half brake pedal travel will barley stop vehicle. If I really put some leg force into it, it will stop the truck.......

Decided to try bleeding the line, (grasping at straws) started at RR, LR, RF then LF. got no bubbles, reservoir never got below half.....

No joy, exactly the same thing.....

Just dont understand, everything good, get up the next morning, no brakes....

Any help is greatly appreciated!!!!

 

Update....master cylinder replaced and re-blead the lines, no dice......i guess the only thing left is power booster?????

 

Sounds like you figured it out by replacement. The booster can be checked by pulling a vacuum on it and see if it holds, but I'd lay odds that's the problem. If you have access to a scanner (like actron or similar) you may want to make sure that no other DTC's have been set before you decide to spend the money on the brake booster.

 

The standard test for all vacuum boosters is to turn the vehicle off, exhaust all vacuum from the booster until the pedal is rock hard. Press the booster with your foot as if it were a normal brake application, and crank the truck. The pedal should fall slightly. If not, the vacuum diaphragm is leaking and the booster needs to be replaced. If so, move to step 2.

Step 2, with the truck running, just barely press the brake pedal and keep slight pressure, if the pedal moves more than 1/4 travel or 1.5" without much force, the valving in the booster is leaking and the booster needs to be replaced.

Since you already said it moves halfway down with little effort, and the pedal is hard with engine off(means no air in system) , i'm fairly confident its the booster.