Yes it may be the brake booster or the check valve.
Do this check.
Check the brake power booster by pumping on the brake pedal while the car isn't running. Continue pumping until you've "bled off" the vacuum from the booster.
Hold the pedal down while you start the car. The pedal should go down a bit more beneath your foot. If it doesn't, then you should examine the connection between the vacuum hose of the brake power and the engine's vacuum.
I would do a real good visual all around the booster. The plug O-ring that plugs into the booster as these get hard and may be cracked or not tight around the booster vacuum hose.
Then check all around the front of the booster area. Have someone apply the brakes and look and listen.
Your vehicle is obviously in good shape with the miles you have. So it is time to have hoses, boosters etc start to wear.
January, 2, 2009 AT 1:23 PM
Thank you for the info. I did what you suggested and pumped the break a few times, held it down and started the car. The petal went down. The noise is definitely coming from inside the car. While the car was running I examined the brake petal and listened where the noise was coming from. There is a black rubber boot where the petal goes into the fire wall. I think it is split on top where I could not see. However, I pushed it in and the sound quit. I doubt this will last. What is this boot called? Can you buy them separately?
January, 2, 2009 AT 2:57 PM
Well, it looks like your booster is okay. But the boot is torn. That boot goes around the shaft that connects to the brake pedal and then into the booster.
From what I am told by the MB parts department it is not separate. You must do the whole booster.
The cost of a booster depending on what options you have can be from about $484 to $540. I just went to a web site I get MB parts from and they wanted about $600 beans. So in this case the dealer was cheaper.
To me Ted, unless the booster gives you problems I would leave it. Now you can get rubber glue and try that but I think it will tear in another place. You have a few miles on the ML which means it has been good to you. If you think how many times brakes are applied daily, times weekly, times yearly.I am surprised they last this long.
My advice. If you do decide to change the booster.I would change the master cylinder also. Will it cost more. Of course. But you have to take the master cylinder off anyway. It has just as many brake applications as the booster. It is only a matter of time.