I recently changed the brake booster with a remanufactured one and when I first initially tested it, the pedal was slow to rise every time it was pressed. The one thing I noticed was that the rubber boot seemed like it was causing it not to fully extended and creating a suction when pressed on.

so I pulled the boot up slightly so that it was not clamped under the flange. And it seems to help.

but recently, my mother was driving the car and jus noticed that when she pressed it in, the pedal was slow to rise for the first inch and then quickly releases. It happens when you press the brakes as hard as possible down to the floor. I didn’t notice it until then because I press it enough for it to fully stop and didn’t see the issue. During the slow release and the car is still in gear, the car was not moving until the pedal quickly released and brakes disenaged.

so any ideas where this issue is caused by? Is it an internal problem with the booster? Or could it be a problem with the master cylinder spring when pressed in all the way?

fyi I set the piston rod the same distance as the old booster.

thanks

 

any ideas?

 

I answered this exact post November 24th ... no response.
11-22-19, 08:37 PM
11-22-19, 08:37 PM
Now you are asking again. (?)

So, again,
The booster evacuates air from both sides of the diaphragm at rest. When you apply the brakes, the control valve allows atmosphere into the rear chamber to help you apply force. When you release the pedal, the control valve allows atmosphere to flow into the front chamber to release the brakes, then vacuum is applied to both when your foot is off the pedal. It is important that the pedal rod side of the booster allows air in, or the booster will not release.
Colin

 

Sorry about the redundant post. I didn’t realize that I posted something about it a while back and didn’t get any notifications that others responded.

when installing the new booster, I made sure that the pedal rod side bracket that screws on was installed at the same length as the original. Brakes were bled too.

I would assume that the spring from the MC would be enough force to start releasing the brakes back, but you are saying that it may be that there is not enough air getting to the front of the booster chamber to release it?

does this mean that adjusting the pedal rod side more may help this?

It only happens when the pedal is pressed all the way down to the floor. The pedal releases fine when not pressed to the floor.

 

Think "air" not spring. The surface area of the booster diaphragm X vacuum from the engine can easily overwhelm the spring. Look for air entry point, listen as well, right at the pushrod as it goes through the floor. You may have an internal/external obstruction at full travel down.
Colin