BOOSTER or MASTER CYLINDER cause the car to miss up ??
 

The brake was too light when pushed, that's means time of MASTER CYLINDER to change. The car ruining perfect in this time.

Now, the brake is too hard when pushed (like rock) & at the same time car start serious bucking problem & idle dropped down to 500-600 rpm, my friend tolled me this is because the BOOSTER damaged.
He pulls the vacuum line that's connected at the top of the BOOSTER & close the line by his finger, the car idle good no miss up.

Did the BOOSTER or the MASTER CYLINDER cause the car to miss up ?

Your master cylinder has nothing to do with vacuum. It's your power brake booster. I've seen the problem before, forget passing emissions if you have them until you replace the booster.

does the booster make the car bucks & hesitate & idle to drop to 500-600 rpm ????

why its related to emission !!

The booster can leak internally. Remember, it operates on engine vacuum.

I agree, it's the booster.

If the booster is leaking vacuum, your computer will read the low vacuum as open throttle and inject more fuel.

No, just replaced. Try plugging the vacuum line that goes to the booster, and driving the car. If the driveability problem goes away, you've found the culprit.

that's why I smell unburned fuel.

can be the booster repaired ?

The booster's diaphram is damaged, and the booster needs to be replaced. The damaged diaphram will result in a vacuum leak, which will cause the engine to idle rough, and will make it very difficult to use your brakes. I suppose someone somewhere rebuilds boosters, but I've never known them. Just replace it.

Take care,
-Chris

Some places do repair them, but it costs more then buying a new one. Makes no sence to me.

Is there any difference in brake booster betwwen COBRA & GT ?

Not that I'm aware of.

Take care,
-Chris

Yes there is a difference in boosters.
Check out this webpage, #5 Brake Booster Upgrades
http://www.geocities.com/mjbobbitt/mustang/brakes.html

BENDIX make the Brake Booster for Ford, I checked their site & I found that Cobra & GT have the same part no.

Last update:

BENDIX make the Brake Booster for Ford, I checked their site & I found that Cobra & GT have the same part no :confused:

www.bendixbrakes.com