My parents have a 2001 Ford Ranger V6 4.0, Auto, 4x4. About 150k miles

They have a brake issue that we have not been able to solve . . .

Occasionally, when braking and rolling to a stop, the brakes will suddenly just release when you hit about 5-7 miles an hour . . . the pedal won't sink to the floor, maybe just a half inch, but it will stiffen and you just can't stop the truck. It just keeps rolling. It's scary.

Only when you have your foot on the brake and you are in your last 20 feet of coming to a gentle stop . . . the brakes just let go.

They have had the master cylinder replaced, the brake booster replaced, and that brake distribution box thing replaced (where all the brake lines go in - mounts just below the master cylinder) . . . none of these have fixed the problems.

The braking system has been re-bled several times, but nothing has helped.

Is there something else that we are missing? It is so intermittent - it seems to be fine when the system is cold, then it happens most frequently after you've driven for a while, parked the vehicle, then gotten back in to drive home . . . And it only happens at low speeds when you are approaching a stop. Doesn't have an issue braking at higher speeds.

Any ideas or advice would be so greatly appreciated. Thank you!

 

The 5 brake line "thing" is the 4wheel ABS unit and its about the only thing that could cause what you describe
It can release brake pressure to the wheels, so no brakes, but unusual for that failure mode

You need special software/tool to bleed 4WABS units, its different than bleeding the wheels
You may need to have a shop with the software and tool bleed the system

There is no reason for air to get into the ABS unit in the first place, did the Master ever run dry?
Or were the brake lines on the ABS unit ever removed before this was noticed?

You can use a Bluetooth OBD2 reader and ForSCAN software to see if there are any ABS codes
Most OBD2 readers won't see those codes

 

Not completely sure if this is the same problem.
I will be driving, not always slow, and I brake pedal drops some, then recovers.
I was told I need the Booster replaced.

Just saying.
If you are taking the truck to a shop, have them check it all, no sense to get it partially done and have to take it back later.

 

Thank you, Ron and Scrambler.

Yes, the ABS unit may have gone dry when a brake line rusted through about a year ago. There was sediment in the master cylinder, so that was replaced at the same time as the booster a few months ago.

So with a new 4WABS unit, new brake booster, and new master cylinder, I guess maybe the answer is to find a place to try and re-bleed the system.

But if it only happens at low rpms and low speed, could that be something else?

Again, thank you all so much. If we can solve this mystery, I will be so grateful.

 

Old ABS unit was probably OK just has air in it
And new one as well, they need to be bled when installed

At low speed/low RPM vacuum is high, so power assist would be replenished if it was leaking

Easy to test booster
Start engine and take foot of the brake pedal
Turn engine off and do NOT touch brake pedal
Count to 10
Press pedal down 4 times, pedal should get hard to press around the 3rd or 4th press, if that happens the booster is not leaking and is holding vacuum like it should
If pedal gets hard right away then its leaking vacuum

When you pair up a Master and Booster there is an adjustment nut that needs to be touching the masters piston when master is seated all the way on the booster
Not hard to do, you can feel if booster rod is to far out because of masters spring holding the piston
But you can't feel if its too loose, so you adjust the nut out too far and then back in
I doubt this would cause your issue

 

Ive got something similar happening, some times i have good brakes, sometime i hit the pedal and it sinks to the floor, sometimes i'll be riding the brakes and then it sinks to the floor so i gotta pump em again. Ive topped off the brake fluid reservoir and monitored it, im not losing fluid anywhere. Hasnt been a major issue yet (i.e., i havent crashed yet) so im just gunna ignore it

 

JoeVR,

How's this going ?

Got Brakes Yet !

 

Do you hear a buzzing noise when brakes let go? Sounds like intermittent/unwanted ABS activation. To test you'd need a scan tool capable of watching all wheel speed sensors when problem occurs. Or pull fuse and see if problem goes away. Visually you can check for broken wires in the front or metal on the rear sensor.

 

Guys!

The mystery has been solved! Today was a day of triumph.

I came across a small light gray vacuum line that was chewed through (or maybe just cut). It was on the passenger side, above the inner wheel well lining, under the blower motor, and out of sight. I connected it with a little coupler and VOILA . . . the brake problem is solved. I am amazed at how much havoc was wreaked by that one tiny little open vacuum line. It's inside diameter was smaller than a WD-40 straw. Wow. Who would have thought.

Wow, I can't thank you all enough for your help with this.

For those of you who have similar problems with your brakes, check ALL your tiny little vacuum lines and connections.

Thanks again, Ron and everybody. Sending best wishes to all.

JoeVR

 

OK, glad its fixed but that wasn't part of the brake system........................., or even engine vacuum system really

Grey vacuum line coming out of firewall is for the AC(air conditioning) system, it goes to heater hose by-pass valve, its vacuum comes from Heater Control panel in the cab, which gets its vacuum from the Vacuum reservoir(black ball) passenger side front of engine bay, down low
Vacuum reservoir has a check valve so a leak won't effect engine......or brake booster operation

But as said, glad its work, but I have no idea why, lol