I think i am leaking vacuum from somewhere.. but not sure where.. (not the booster though..)

Here is my problem:
When i start the car up and drive, brakes are fine for about 30 seconds..
After that, they work, but really hard and the wheels won't lock..
If i drive 30 and punch the brakes all the way the car will slowly stop and the brake paddle becomes hard...
If i am at the stop light and i am in 'D' and puch it all the way it's hard.. but if i put it in 'N', it's gets better.. Going really slowly and punching the brakes will stop it slowly, but going slowly and shifting to 'N' and then punching it will lock the brakes and stop it on the spot...

What gives??

I replaced the master cylinder.. It was leaking anyways, so i finally replaced it with a brand new one.. but still no go.. Whice it was outside (the MC) i checked the booster and i think it's fine and no fluid got into it.. (the rubber seal was dry..)

Help?

I would start with replacing the check valve on the booster. A lot of times this will leak vacuum without you noticing it. Also, make sure your vacuum hose and fittings on the motor aren't leaking.

Joe

Did you bench bleed the master cylinder? If not, there is most likely air in the system.

Originally posted by BlueSS454:
Did you bench bleed the master cylinder? If not, there is most likely air in the system. I did..
No air in the system..

Its not the MC if you are getting a real hard pedal.

Shai,
Did you check the check valve and vacuum hose?

Joe

Originally posted by 72SSAbody:
Its not the MC if you are getting a real hard pedal.

Shai,
Did you check the check valve and vacuum hose?

Joe The Vacuum hose is new.. But the valve is not..
You are talking about the valve that is on the hose itself.. right? from the manifold to the valve to the booster.. right? that valve..
If so i'll check it..
I did try connected the vacuum from the manifold straight to the booster and it didn't work..

Originally posted by ChaosMalibu:

from the manifold to the valve to the booster.. right? that valve..
Correct. It pops right out of the booster and is made out of cheap plastic that can crack easily and cause vacuum leaks.

Here in the states they sell them in the "Help" section of the parts store. I'm sure they have them there in Israel. Just have to ask where they are.

Joe

if you have low vacuum from a high horse motor the same problem will happen
also if the engine is off on the timing this will also cause low vacuum

I was thinking the same thing, check the engine vacuum signal. If you run a high lift cam you will loose vacuum there.

Replaced the valve.. it's better.. (the valve was not good..)
But still.. It's not "That"
I'll check my Vac. (got a vac. gauge)

and update...

Shai,
Are you hearing any "hissing" noise at all with the motor on?

Might want to make sure you don't have a vacuum leak where the vacuum is sourced from the intake.

Let us know how it turns out graemlins/thumbsup.gif

Joe