Odd Brake problem

[SteveD]

Hi
2011 Expedition KR. All brake components replaced less than 5000 miles ago. Now for the issue. This has been going on for less than a week. It felt like my parking brake was on when I took off from a traffic light. It was not engaged. I pull into the driveway and it has a slight incline. I put the truck in neutral and it does not roll back, after 5 seconds it starts to slowly roll back and 10-20 seconds (20-25ft) it is rolling freely. No high heat from any of the calipers and no pulling when the brakes are engaged. When I drive and use the brakes I can now feel the 15 - 20 second full release and the feeling of the parking brake like hold at take off from a stop.
Took the truck to the shop Friday. They think it is the brake booster!!. I am not losing brake pedal pressure when I drive or when I hold the pedal down. I have had a vehicle with a failed booster before. My friend and I are looking at it today. When I turned the truck off he had his head down buy the front drivers side tire. He says he hears air leaking around the ABS unit at the leak lasts about 20 seconds. I got out and he started the truck, let it run for a 30seconds and turned it off and I could hear the air leak.
I have looked on the forums and you tube and I am not finding anything. Any ideas would be greatly appreciated!
Thanks

 

[Hamfisted]

Is it a 4x4 ?

 

[SteveD]

Yes, I replaced all front 4x4 vacuum lines inner hub pieces and wheel bearings when I did the brakes, Air is not leaking rom hub.

 

[grillzilla]

Collapsed brake line

 

[SteveD]

I thought that a hose might have been swollen internally. The shop bleed the brakes and there is no brake fluid " flow " problem.

 

[Motorcity muscle]

Would have that abs unit checked out, was no issue for 5,000 miles and then acts up is very strange. Wonder if you do a hard brake in an open parking lot and see how the system responds. Ford has had some issue's with loss of brakes with no warning, would make me nervous. Hope you have a good mechanic or dealership near you.

 

[Spaznaut]

My wifes '10 had a similar issue but it progressed to a bad pull to the right. Ended up being a frozen slide pin on the bottom right caliper bolt. Greased it up and works great. I also replaced the brake lines while I was at it (found the pin while replacing the lines thinking I had a collapsed one). I'm not sure on these vehicles if you can pull a fuse for the abs and see if it makes a difference. Also does it do this while cold or when hot? I don't think a vacuum leak would cause the brakes to stick but would make the pedal much tougher to push and engage. Good luck and keep us updated on what you find.

 

[SteveD]

Answer to Motorcity Muscle - Hot or cold
Answer to Spaznut - I am going to pull the fuse today. I still think it has something to do with the air leak at or near the ABS unit I hear when I shut the engine off. Obviously this could be happening while driving but I would have no way of knowing.

 

[Retiredusps]

mY 05 HAD A SIMILAR TURNED OUT TO BE FRONT HOSES . THEY WOULD LET FLUID GO ONLY ONE WAY.YOU HAVE PRESSURE GOING OUT, NO RETURN SPRING ON DISK BRAKES. CHECK TO SEE IF ANY ARE RUNNING HOT

 

[Fastcar]

Caliper or the pins

 

[tommyddsr]

Brake lines collapsing (small rubber ones) will cause this issue. You are applying great pressure (hydraulic) when applying brakes, but upon release it just bleeds down naturally. So you have enough to engage but not disengage properly.

 

[SteveD]

Tested booster and it is okay.
Pulled ABS fuses and test and put them back in one at a time and no difference.
I will post when I find out.

 

[Chawk]

Just had a similar problem with my '07. Turned out to be front brake lines had corroded. Had the mechanic go ahead and change out the master cylinder, too.

 

[Goofy173]

Like grill ills said, collapsed brake line.

 

[Tim Deater]

The hiss could be the 4x4 system. It uses vacuum to unlock the front hubs, and lack of vacuum to engage the hubs with a spring in the hub. The valve that allows the vacuum or vents it is attached to the brake booster in my 2011. To know if that is it, start the truck, put it in 4high, give it a minute or so then turn the engine off leaving it in 4H. Should not be that hiss as that system would of been vented already.