Bad booster?

[281pony]

i have had an ongoing issue with my brakes that seems to be better, then worse. the car does not stop good at all, let alone considering it has cobra brakes.

setup;
v6 master cylinder, stock booster
m2300k brakes

issue; the pedal is hard, which is fine, however, i can STAND on the pedal and it's like the brake pressure is progressive. almost like im wearing off a layer of ice on the rotor and it slowly stops stronger and stronger.

i am not hearing the hiss sound i've searched and seen referenced. with car off the pedal is very solid but it slowly goes to the floor with solid pressure. i cannot pump the pedal up as i drive, lastly i'm losing no fluid.

just feels like my pedal pressure is not in coordinance with the braking.

 

[1990MustangLX50]

Was your stock Master cyl. leaking? It may of leaked into the booster, have you tried to bleed your brakes, it could be air in the lines.

 

[jrichker]

Power brake booster test:
1.) Check engine vacuum you should have 14"-18" of vacuum at 625-750 RPM, 18"-21" vacuum at 1000 RPM.
2.) Vacuum checks good, start car and run engine up to 1000 RPM for 30 seconds.
3.) Cut off the engine and then press the brake pedal 3 times. It should get harder to press and travel less each time you press it. If it doesn't, then the brake booster is suspect.

Check the power brake booster grommet and the vacuum check valve to make sure that they are in good condition. The grommets get old and leak vacuum, reducing the vacuum available for the booster operation.

 

[281pony]

i have a little less vacuum at idle and 1000 rpm's then you mention. however, the car is cammed and i know that can affect vacuum. i'm sitting at like 14-15 at idle 840 rpm and like 17-18 at 1100 rpm's.

the car makes a quick "huff" noise if i jam on the brake pedal really fast, but i think that is normal. i am not hearing a hiss or anything abnormal while holding pressure.

the pedal pumps up for 3 pumps also.

ill drive it again and see if it continues to do it. the pedal itself feels fine, it's just like the brake pads are slipping and then progressively start to grab. not a real good feeling

 

[Mustang5L5]

What pads and rotors are you running?

Brand?

 

[281pony]

What pads and rotors are you running?

Brand?

brembo rotors, unknown pads.

i thought he told me they were oem or hawk pads.. good life on the pad, however it was making noise from the pad walking.

 

[Mustang5L5]

Some types of Hawk pads don't really grab well when cold. If you go out and really brake hard, does it improve? If so, it could just be a pad that shouldnt really be on a street car.

The OEM pads however, do have good cold bite to them really.


Is that what it feels like?? The pads need heat to stop well?? So if you were to get the brakes nice and toasty does braking improve?

 

[281pony]

Some types of Hawk pads don't really grab well when cold. If you go out and really brake hard, does it improve? If so, it could just be a pad that shouldnt really be on a street car.

The OEM pads however, do have good cold bite to them really.


Is that what it feels like?? The pads need heat to stop well?? So if you were to get the brakes nice and toasty does braking improve?

thats closer to what im experiencing yes. it seems like i hit the brakes a few times and the pads get warmer and grab better.

then by the next time i hit brakes, they are cold again and won't grab unless i do a panic brake. which is just jamming on them and they progressively grip stronger

it is starting to get cold here for winter, but i wouldn't think weather would affect the pads so dramatically.