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What is wrong if my car shakes when i press the break pedal?

I have a 98 Ford Taurus. I have replaced my mass fuel sensor, air filter, oxygen sensors,and my spark plugs. But i still have the same problem. That problem is that my car shakes whenever i have the brake pedal pressed down and the car is in reverse and drive.

My Transmission fluid is only a little silver above the full line. The only thing that myself, my boyfriend, and dad can figure out is that it is either my automatic clutch gears or my transmission.

Any Help?

Rotors is my first guess!

It this only happens when the car is moving and you press the brake pedal you probably have warped rotors. Get on an empty stretch of road or empty parking lot and while moving forward hit the brakes and then release them. If the shaking comes and goes with the brakes it is probably the rotors, you should have a mechanic take a look at the brakes

I’ve been testing my car all day. And it is just when i first take it out of park and whenever I am holding the brake pedal down for more than 15 seconds.

Well, if it doesn’t matter if you are moving or not, I’d suspect a massive vacuum leak in the braking system.

Two questions:

  1. What happens to engine RPM when the shaking starts? (If you have a tach.)
  2. Turn off the car with the brake pedal depressed. Does the pedal “firm up” very quickly?

Look and listen, there is a rubber vent hose near the top of the engine on the passenger side that often deteriorates and leaks causing a poor idle, worse when idling in gear. Often you can wrap your finger around the split and slow the leak enough to greatly improve the idle.

That’s a SWAG…

Are you saying the engine runs rough when you step on the brake pedal?? Check the vacuum line that connects the power brake booster to the engine, then have GOOD brake shop test the booster unit itself to see if it holds vacuum…

This is probably the cause, it goes from the Throtle body to the top of teh valve cover. For a short term fix you can close the hole with some RTV (ruber) or some duct tape, but you should get it replaced by either buying a new hose from the dealer, or finding some bulk ruber hose and cutting it to the right dimentions.