Impala Forums banner
1 - 6 of 6 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter · #1 ·
First time here and hoping for a solution but willing to take suggestions.
I've got a real "head scratcher" for you guys.

07 Impala (VIN: 2G1WB58K079104049)

After 8.5 weeks at the Dealership they are throwing in the towel on why the brake pedal goes to the floor. BTW, we went through 3 different field service engineers at the dealership, a shop manager, and a couple of service mechanics too.
This all started when my son came home from school after his spring semester and we changed the pads and rotors. We used OEM parts except for rear rotors due to availability. Bled brakes (two man) several times (RR, LR, RF, LF) but brakes were intermittent - good one minute but pedal to the floor the next. It acted as if it either still had air in the system or there was a loss of pressure or fluid leak but absolutely no leaks ever appeared. We then changed the master cylinder (aftermarket) after sufficiently priming it prior to installation. When the same problem persisted we brought it to the Dealership.

The Dealership diagnosed the problem as a faulty brake booster (aftermarket) and changed it. No change in the brakes. No codes with the scan tool from the Dealership. They repeatedly bled the brakes with the scan tool to activate the ABS to remove air and air would come out each time and brakes would work fine. But the next morning the pedal would go back to the floor and there would be air in the system.

It is puzzling how air can enter (whether passively or actively) the system without fluid leaking out. To me, this defies logic and I do not believe air can enter the system passively so it would seem that air is being actively introduced somewhere. Could this occur between the brake booster and the master cylinder. Is it possible that the booster can push air into the master cylinder and somehow completely sealing (like a check vale) upon recoil and not allow fluid to leak out when brakes are disengaged?

If you can solve this riddle you should promote yourself from master mechanic to Jedi.
 

·
Registered
Joined
·
36 Posts
Shade tree mechanic here. Your description sounds like the master cylinder is allowing fluid to bypass the plunger. Your write up states they changed the booster, to me that is odd. Guess it could also be one of the calipers failing. Easy test; use a vice grip on the rubber line leading to each caliper and test one at a time.
 

·
Registered
Joined
·
2 Posts
Discussion Starter · #3 ·
Shade tree mechanic here. Your description sounds like the master cylinder is allowing fluid to bypass the plunger. Your write up states they changed the booster, to me that is odd. Guess it could also be one of the calipers failing. Easy test; use a vice grip on the rubber line leading to each caliper and test one at a time.
Thanks, ritalz. you may be onto something because when the rotors and pads were changed, the front driver piston popped out of the caliper but was successfully reseeded back into the caliper. As I understand it, that seal is designed to prevent fluid from getting out (and it does) but that doesn't mean that air isn't being sucked back in upon recoil. Thank you, sir.
 

·
Registered
2004 Impala LS 3.8L (~130k miles)
Joined
·
252 Posts
Job #1 is to fire that dealership.....seems like they're incompetent to the point they don't want to see your vehicle again. Difficult to believe a dealership service center, focusing on Chevrolet, is unable to resolve the issue. I would try the following:
  1. Check to see if the vehicle is reporting any diagnostic codes
  2. Check to ensure there is adequate brake fluid in the master cylinder
  3. Check for any fluid leaks....if fluid can leak out anywhere, air can certainly get in (i.e., brake lines and hoses intact?)
  4. Since "this all started with the rotor and pad change", you might want to go back and ensure nothing was damaged during the installation
  5. The test suggested by ritalz is good.....if the pedal is going to the floor, try isolating which line/wheel cylinder is problematic by testing them one at a time
  6. If the problem persists, then another brake bleed is in order
    1. Bench bleed the master cylinder
    2. Bleed the entire system one line at a time in the proper sequence (don't know that sequence for your vehicle but usually start the process with the wheel cylinder most distant from the master cylinder)
    3. If the ABS has air, you might need to have a "competent" mechanic bleed the system using special bleeder tools
Let us know how it goes......
 

·
Registered
Joined
·
494 Posts
When I have replaced calipers in the past, I've had good luck gravity bleeding the whole brake system. Start with not letting the master cylinder run dry. Open the bleed screws on all the calipers. Watch the bleed screws for fluid to flow out, while keep pouring brake fluid into the master cylinder. You will see bubbles at the bleed screws for a while. When the bubbles stop, and you see a constant flow, close the bleed screws. Then do a traditional 2 person bleed procedure. I also like to suck the fluid out of the master cylinder reservoir with a turkey baster, then refill the reservoir, so the whole system has clean fluid throughout when finished.
 

·
Registered
Joined
·
44 Posts
Two things from the info you allowed us
The caliper ...piston fell out ??
You replaced the master and you say you bleed it before you installed it ...after it was installed.and you started bleeding rear right ..did you come back and crack the fittings at the master..a fast crack is needed to release trapped air...
.after that gravity bleed starting at rear right is best as to not damage a new master...
It's possible master is damaged or the caliper where piston fell out.
 
1 - 6 of 6 Posts
Top