Not an SN - but could really use some other brains on this one.

[gate keeper]

Hey guys - it's not an SN but it is a Mustang. 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 ride:

 

[CC'S95GT]

It has hydroboost right?

 

[gate keeper]

It has hydroboost right?

Everything I can find onlline, shows that stopped in '04 - so I'd have to say no.

 

[Burninriverdiver]

I've changed a lot of brakes, and I had an "off" day installing calipers on my truck. Installed them on opposite sides (which bolted right up), kept bleeding them and it took a day of thinking to realize the bleeders were on the bottom because I installed opposite. It seemed to bleed correctly which threw me off until I realized there had to be trapped air at the top of the calipers. Switched them around and problem solved.

I highly doubt this is your problem but I hope it's something as simple as this. Good luck and keep us posted

 

[CC'S95GT]

vacuum leak in the brake booster?

 

[daltonduree]

maybe its the abs unit. the part that takes the fluid in when it releases the brake. if that valve had a issue then it would go right to the floor without any brake action

 

[DeepList]

maybe its the abs unit. the part that takes the fluid in when it releases the brake. if that valve had a issue then it would go right to the floor without any brake action

ABS is supplemental and not used during normal braking operation.

 

[daltonduree]

^ No. ABS is supplemental and not used during normal braking operation.

i re read his issue and that doesnt make sence...

 

[daltonduree]

definatly air in the system somewhere. what method are you guys using to bleed the brakes?

 

[g36 monkey]

vacuum leak in the brake booster?

This is where I'd be checking assuming you know you bled the brakes right, starting in the passenger rear, then driver rear, then passenger front, then driver front, making sure every last bit of air is out of the lines, and making sure the new master is bled as well.

Do some google searches for vacuum smoke tests. They make all the difference in the world

 

[96gt4.6]

did you bleed the master cylinder?

 

[gate keeper]

I've changed a lot of brakes, and I had an "off" day installing calipers on my truck. Installed them on opposite sides (which bolted right up), kept bleeding them and it took a day of thinking to realize the bleeders were on the bottom because I installed opposite. It seemed to bleed correctly which threw me off until I realized there had to be trapped air at the top of the calipers. Switched them around and problem solved.

I highly doubt this is your problem but I hope it's something as simple as this. Good luck and keep us posted

- good thought and appreciate the input, this SSBC kit has three bleeders on each, top, middle/side and bottom.

definatly air in the system somewhere. what method are you guys using to bleed the brakes?

Been bled w/ the car off until brake appears - been bled with the car running, but brake never appears. always pushes through w/ 10% of brake power.

This is where I'd be checking assuming you know you bled the brakes right, starting in the passenger rear, then driver rear, then passenger front, then driver front, making sure every last bit of air is out of the lines, and making sure the new master is bled as well.
Do some google searches for vacuum smoke tests. They make all the difference in the world

Followed that pattern exactly - we'll have to look into the smoke test.

did you bleed the master cylinder?

Sure did, on the bench before it was installed.

Told ya it was being tricksy

 

[95opal]

Hey guys - it's not an SN but it is a Mustang. 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 ride:

The brakes are nice and solid when the cars off cause theres no vac assist...did you physically try turning the wheel with the brakes on engine off?
Is the pushrod in the master properly installed? When you bled the brakes did you have a good solid stream of fluid?

BTW the ride is sweet..

 

[gate keeper]

The brakes are nice and solid when the cars off cause theres no vac assist...did you physically try turning the wheel with the brakes on engine off?
Is the pushrod in the master properly installed? When you bled the brakes did you have a good solid stream of fluid?

BTW the ride is sweet..

Thank you - and thanks for the input.
Yes - when the car is off and the brakes are pushed they work/act as normal and grip perfectly.
Yes - we are actually on our second master and the push rod was properly aligned.
Yes - a good solid stream - no air.

See why we're banging our head on a wall?
Brakes - admittedly - are not our thing, but damn if we haven't tried everything we can think of.

The killer variable to keep in mind is this:

The brakes were PERFECT from November till two weeks ago and then out of no where let go and thus began this whole debacle.

 

[95opal]

Well the only thing I can say if there are no leaks and everything has been installed correctly and the lines are bled....You have a bunk master, not sure where or what kind it is but that's what Id be banking on.

 

[daltonduree]

check your brake hoses and make sure one isnt swelling up huge. maybe try starting it and loosening lines from top to bottom looking for flow of fluid. also it the adjustment on the booster correct?

 

[96gt4.6]

you say you have tried a 2nd master, have you tried a second booster. I would say a vacuum leak somewhere or the new booster is leaking.

 

[95opal]

you say you have tried a 2nd master, have you tried a second booster. I would say a vacuum leak somewhere or the new booster is leaking.

A booster problem or vac leak would lead to a very stiff pedal but wouldn't affect the clamping ability of the caliper.

 

[rz5.0]

I've heard about the abs unit been a pain in the ass to bleed in the newer cars. But I would also think MC...

 

[96gt4.6]

A booster problem or vac leak would lead to a very stiff pedal but wouldn't affect the clamping ability of the caliper.

yea i guess i was just thinking that's the only thing that really changes when starting the car, that and maybe the abs