2007 F-150, SInking Brake Pedal

It's not normal. Well, it IS normal if the Brake Master Cylinder is not working right.

The master cylinder has chambers inside, and the brake pedal is connected to a piston that passes between these chambers. The piston has o-rings and seals and stuff of that nature. If the pedal drops, then the o-rings and seals are not working properly, typically as a result of wear, but I can't imagine enough wear in an '07 truck for anything to not be working.

As a test, try pumping the brake pedal a few times to see if it comes back up and becomes more firm. If so, then this confirms the master cylinder is not working. As you continue to hold the pedal in the new position, and it falls again, then this double confirms that the master cylinder is not working properly.

As a practical matter, you should be in the habit of only holding enough pressure on the brake pedal to keep the vehicle stationary.

Jeff, thanks very much. This is what I suspected but the lazy service department didn't want to deal with it. He told me it was due to some new technology, sort of like "fly by wire" where the pedal isn't actually connected to anything that manipulates the brakes, but simply sends and electronic signal to something that is. That may or not be true but there is no way the pedal should be getting soft just sitting at a light. The truck only has 3000 miles on it and has done this since day 1.

And yes, the pedal pumps right back up. After about two minutes it will sink again. If there is a problem, it's only a matter of time before something goes wrong while trying to stop.

Thanks!

LHA

There is a chance that the service writer could be correct then, but I had no idea that the '07 F150 was a fly-by-wire. If it is even remotely convenient, take your truck to a different dealership.

I don't know how a fly-by-wire brake system works, and there is a chance that a sinking pedal is normal. But I also try to stay on top of this sort of thing, and putting a fly-by-wire system in anything other than a luxury or luxury sports car is beyond where I thought the technology had gotten to. These systems (fly-by-wire) are generally held to high-end models where space is at a premium. BMW has a few fly-by-wire models, but they do it because they found it easier than the mechanical linkage that they would need to employ otherwise.

I'm not trumpeting BMW, nor neglecting others, but I can't foresee the reasons why a Ford F150 would be fitted with fly-by-wire, especially on the braking system. Even BMWs fly-by-wire system is on the gas pedal not the brake. I do not recall any instance where fly-by-wire was used on a passenger car brake system. I'm not suggesting it is not feasable -- they use fly-by-wire brakes on airplanes, and have for a long time -- but I've not heard of them using it on a passenger car or light duty truck.

PS I've read reports that people are not getting used to fly-by-wire gas pedals very well. They (the fly-by-wire systems) seem to have a different feel that people are not comfortable with.

Ford started "fly by wire" wire only electronic throttle in 2005 on the Ford Super Duties, I am fairly certain that the brakes DO NOT use "fly by wire". I don't believe the brakes are a system we will see changed to "fly by wire" any time soon...

I'm going to take it to another dealer as Jeff suggested and insist it gets fixed. It just doesn't feel right to me.

There's no such thing as "brake by wire". Not yet anyway. The ABS system can (does) bleed the pedal down on one of my cars. It's not supposed to at a light, of course. I don't have an 07 F150, so I don't know how the ABS system was built on that.

I have an 06 F150 with the 4.6L. I do not get in a hurry driving this truck. Throttle response sucks. I have read that the Mustangs are the same and a work around exists to help the computer with the lag.