Could Use Some Help With Our Show Cars Brake System - Thanks.

[TMIproducts]

Hey guys - Our 05 GT is giving us grief and we are scratching our heads to what the heck is going on.
Car's got all new SSBC brakes and rotors - and had factory booster, and master cylinder.
Going down the road two weeks ago - pedal goes all the way to the floor - no brakes, no fluid leaking ... no idea. (thankfully no one was hurt, nor was the car).
So we replace the Master Cylinder and the Power Booster - basically the only thing that is original are the brake lines.
When the car is off - there is plenty of brake, nice and solid.
However, when the car is ON - pedal can be pushed all the way to the floor and we've got like 10% of our brake.
When the car is up in the air - we do not have a single drop of brake fluid hitting the ground, all lines are solid and brakes bleed as normal....

At a complete loss now and this car is set to be shot for 5.0 in a weeks time - at this rate the beast won't even make it to the shoot!!

Any ideas? Thanks guys.

Here's the car:

 

[madspeed]

improper master cylinder for those bakes?

 

[Route666]

I've never looked at how ABS systems work but I imagine there is some sort of bypass valving in it, maybe it is plumbed or wired incorrectly (so only noticeable when ignition is on) or just plain faulty?

 

[Az Pete]

Getting the ABS bled may help. Have you double checked the pads for odd wear.

Just had the same issue with my grandsons 93 low miles Explorer. Replaced rear cylinders, booster, two master cylinders and thought the year old front rotors and pads were good. Finally checked them and found extreme wear...as in bad pads. Replaced rotors and pads and now we have great brakes. Do not "think" something is good just because it is newer.

 

[Route666]

Oh and my Harley was having a squishy brake lever - calipers needed rebuilding, pistons were stuck in the seals and retracting back into the caliper after each brake application - maybe a similar thing is happening here? I replaced the master cylinder thinking that was the problem as it only appeared after I installed a chrome one.

 

[Noobz347]

@[USERGROUP=77]SN Certified Technician[/USERGROUP]

 

[jrichker]

Disconnect the power (fuse or electrical connector) from the ABS and see what happens...

Since the ABS is only working when the ignition is in the Run state, and the problem goes away when the ignition is off, the ABS is suspect. Removing power from the ABS system or disconnecting the ABS control valve shuts down the ABS, and allows you to eliminate another item in your list of suspects.

 

[Mustang5L5]

I would suspect ABS as well in this case....especially if the brakes did work fine at some point. You mentioned the issue not starting until 2 weeks later, so I assume for 2 weeks you had good brakes

 

[TMIproducts]

I would suspect ABS as well in this case....especially if the brakes did work fine at some point. You mentioned the issue not starting until 2 weeks later, so I assume for 2 weeks you had good brakes

For THREE MONTHS we had good brakes - then boom - doing 35mph we lost all brakes.
Pulled over, and checked the brake fluid - full, no loss of fluid.
Got it home and up in the air - no drips, no fluid anywhere.
From there, we bench bled and replaced the master and the booster.
All back together, bled the brakes from passenger rear over and still - no brake when the car is on.

Trying to figure out what could have gone wrong so quickly - I like the idea above about pulling the plug on the ABS system and seeing what happens.
I'll let you know on Monday.

Thanks guys!

 

[Az Pete]

When not running, the lack power assist will make the brakes feel like they are good. When running is the time the brakes should work. One cannot compare the two when power brakes are involved. My grandsons '93 Explorer was the same, plus his brakes just went bad one day......