Brake pedal SUPER stiff on 99 Cobra?

[DarkRattle]

So my brake pedal is super stiff, when I push in the brake pedal I can hear a hissing noise, so I went ahead and bought a new Motorcraft hydroboost brake booster to get on there. So I want to know if it truly is the booster or can it be the lines or maybe calipers? I pumped the brakes with the car off and then put pressure on the pedal, when I turned it on it sunk in maybe 1/2 an inch. What do you guys think?

 

[Dave.O]

Sinking somewhat from car turned "off" to "on" is normal due to hydro/vacuum assist of brake booster on any car that has it.
how much it sinks is probably relative to amount of assist.
that being said, 1/2 sounds about right.

if you pump brakes with car on does it make a difference?
as long as the pedal doesn't sink to the floor and you still have good braking I wouldn't worry about it

I personally like a really hard pedal so I run SS lines on all my cars, not sure if that really makes that much of a difference though

 

[DarkRattle]

Sinking somewhat from car turned "off" to "on" is normal due to hydro/vacuum assist of brake booster on any car that has it.
how much it sinks is probably relative to amount of assist.
that being said, 1/2 sounds about right.

if you pump brakes with car on does it make a difference?
as long as the pedal doesn't sink to the floor and you still have good braking I wouldn't worry about it

I personally like a really hard pedal so I run SS lines on all my cars, not sure if that really makes that much of a difference though

The thing is the braking is not good, I have to put a ton of pressure. I went ahead and bought a new motorcraft booster and master cylinder just to swap it out in case. How hard of a job is it?

 

[Dave.O]

its not difficult. hardest part will be bleeding the system.
Make sure you bleed master cylinder first (right below reservoir) before going to all 4 corners. I failed to do this once and it took me hours to figure why the peddle wouldn't pump up.
to bleed the hydroboost turn the rack lock to lock repeatedly before starting engine, it will help prime system.

 

[DarkRattle]

its not difficult. hardest part will be bleeding the system.
Make sure you bleed master cylinder first (right below reservoir) before going to all 4 corners. I failed to do this once and it took me hours to figure why the peddle wouldn't pump up.
to bleed the hydroboost turn the rack lock to lock repeatedly before starting engine, it will help prime system.

Ok, good to know, thanks for the help

 

[01yellercobra]

Get something like the Motive bleeder. I used one when I upgraded my calipers and lines. It made life so much easier.

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