1995 E300 : brake pedal hard to push, won't turn off
 

Does anyone have any suggestions for diagnosing what to rule out before replacing the vacuum pump?

There is vacuum, reading about 10 or 11 at the little hose that comes directly off the pump that the 5-way connector goes into. There's also a reading of 10 or 11 at another hose (on the passenger side) that goes to a small black canister.

Also, the engine doesn't shut off for ten to twenty seconds. The brake pedal has become very hard to press. The door locks seem fine. Started having these symptoms about a week ago, and drove it a few miles then parked it.

The other thing it was doing is when backing out of the driveway, then shifting to forward, the transmission starts to slip right at that point. Otherwise, there seems to be no trouble with the transmission.

I have owned the car for two years, it has 290,000 miles on it and has been a great car.

2 guesses would be that the brake vacuum hose (the really big one) has a crack in it, OR the booster itself has failed.

yep

It sounds like the vacuum pump is providing the necessary negative pressure. Disconnect it at the brake vacuum booster, plug it and see if it improves the shut off time. If it does not move to the next circuit.

With the vacuum gauge at the hose where the brown line connects to the big black vacuum booster line, I get 13 inches. When I press on the brake pedal, the gauge at that point, goes to zero, and then slowly builds up again.


The reason I am investigating this is that the brakes are hard to press and the car doesn't turn off for several seconds.

Does anybody have any ideas?

thanks!

Update: We disconnected it at the brake booster and applied the mitivac vacuum pressure to the brake booster, it doesn't hold it, goes to zero. When the

Yes! Plugging it at the brake booster does improve the shut off time. Is there something on the other side of the booster that could have a leak? Or does it stop at the booster?
thanks!

Where are you located. I could help you with it in a couple weeks if you are close by.

Thanks! I am Maryland --

:cool:

there is an o-ring on the back of the master cylinder... if it's bad the booster will not hold vacuum.

is this a diesel?

There must be a check valve close too the booster could be your problem.

Pretty sure you'll find the booster itself is bad.
Gilly