Had a guy cut in front of me this weekend while I was doing about 65 mph, had to plant the brakes, the darn pedal went almost to the floor. The thing wanted to stop and would not let me modulate the brakes! She was going to stop no matter what I did with the brake pedal! It was spooky. I know they told me this thing had some sort of "Brake Assist" system, but this seems really unsafe!

Has anyone else seen this phenomenon?

 

With 4-wheel anti-lock brakes, you just mash the pedal and it does the rest. The days of pumping the brakes are long gone.

 

I understand that, same as what I had on my '00 Expedition. But these things would not release until you removed your foot from the brake pedal! That's not too good, if you have someone wanting to get personal with the rear end of your expy!

 

It probably was the EBD (Electronic Brake Force Distribution). The computer senses (thinks) you want to panic stop and applies additional pressure for you.

The EBD should allow you to modulate by sensing that you let off the pedal.

I've experienced slamming the brakes too ('03) and I really noticed how much harder the brakes were applied compared to the amount of force I used. Unlike you I was in a stituation where I did want to come to a complete stop.

Hmm might need to try your situation. If you slam the brakes (induce EBD) then quickly release the pressure on the pedal then the EBD "should" disengage and not intervene anymore. But according to your account, it didn't disengage (?). Perhaps you only experienced that extra sensation from the EBD and it did disengage?

 

Which seems wrong to me, plus the pedal turns to mush, and went to the floor when the EBD kicks in so trying to feel any modulation in the brakes was impossible! Until I had to pull my foot off the pedal and hit the brakes again, then it must have returned to a normal mode. It's a tough deal to test since you need to have a head of steam brewing to recreate the problem. In a parking lot testing I don't think you could recreate the scenario.

 

That is scary! The behavior is not normal or to be expected and is definitely very dangerous. Don't tolerate it.

Could be a combination of mechanical, hydraulic and electronic causes. Stuck pistons, caliper slides, fluid return valves, vacuum assist leaks, sensors, ground faults, etc..etc.

Take to a dealer or a brake shop get it fixed, please. Price is not the issue, staying alive is.

 

Well you're right if your pedal turns to mush then that's not a good feeling.

Like I said, when I felt the EBD it came to a complete stop as I wanted so I was standing on the pedal anyways.

I was thankful when the EBD kicked in during my panic stop as I felt it did reduce the stopping time and distance. But based on what you're describing then that doesn't sound right.

Keep us updated if the dealer tells you something enlightening.

 

Had a similar thing happen with my '03 as well. Twice I've made hard stops at relatively low speeds (<20 mph). The pedal did feel strange; excess travel. It really stopped well, but the front end dove down more than I expected and it kinda scares you. Both times I drove away wondering what the heck just happened . . .

 

Well I swung by my Ford dealer, told them I thought I may have a problem with the brake assit system on my Expy. They gave me the standard slack jaw look, and then asked what's brake assist.

So I crack open my owner’s manual hoping for some enlightenment, and on page 196 there is section on brake assist. I have highlighted the point that concerns me!

The Brake Assist System provides full braking force during panic braking situations. It detects a rapid application of the brake pedal and maximizes the amount of brake booster assist, helping the driver to achieve maximum braking pressure. Once a panic brake application is detected, the system will remain activated as long as the brake pedal is depressed. The system is deactivated by releasing the brake pedal.

When the system activates, the brake pedal will travel with very little effort: this is normal.

So once you get the brakes to think it's in a panic situation the only way to keep it from coming to a complete stop is to release the brake! Plus when the system is active you no longer can control the amount of brake pressure being applied! It's all or nothing.

I'm sure this system does a fine job, but if I had not released the brake completely during my little "brake check" this weekend that suburban would have shortened my Expy!

No so sure I like the Brake Assist system……

 

Evidently you have the optional Advance Track system. That operates very differently than the conventional ABS. And to anyone that wants full control of thier vehicle, that's a disadvantage. If you ever tow a heavy trailer, be sure your trailer brakes go hard on first, or that feature will put you in big trouble.

 

The expy I have does not have the Advance Track System.

From my understanding all '03 Expys have this brake assist system.

 

Yeap