soft hissing brakes, dash warning lights on

[BoogieBot]

I've got a 2000 2.5L RWD Ranger. My brake pedal is really soft and goes 2/3 to the floor before it engages, and makes a hissing sound when depressed. The ABS and parking brake lights on the dash aren't illuminated on startup, but illuminate after a few brakes (particularly if those are hard brakes where I really stand on the pedal).

With the truck off, I can pump up the brake pedal nice & stiff so it barely moves when I stand on it. But if I pump it up and keep pressure on the pedal while starting the engine, the pedal hisses and goes 2/3 of the way to the floor right at startup.

I checked the brake fluid and it's maybe 1 cm below the "max" line on its reservoir. Brake fluid looks cloudy and old - I bought this truck 10,000 miles ago, so I don't know when the brake fluid was last changed (looks like a looong time ago).

The soft pedal/hissing problem has been an issue for a year and a couple months, the dash lights only started showing up in December 2013 when I replaced the battery.

Does this sound like I just need to bleed/replace my brake fluid, or is it something more insidious? I tried searching this forum, but couldn't find anyone with the _exact_ same problems (most folks seem to have either low brake fluid or can't pump up the pedal while the engine is off).

 

[RonD]

The hissing noise is the atmosphere valve on the cab side of the power booster.
Power assist brakes work by using engine vacuum to lower the pressure on one side of a diaphragm(engine side) in the power booster, when you push on the brake pedal the atmosphere valve opens and allows the 15psi(sea level air pressure) to assist you in pushing on the master cylinder.

Hissing is there each time pedal is pushed but usually you can't hear it.
That could indicate a power booster issue.
Power booster has a check valve on the vacuum hose, it's that plastic piece on the power booster end of the hose.
It allows the power booster to hold enough vacuum for 2 or 3 brake pedal pushes if engine should ever stall while driving.
So after running engine turn it off and then see how many pedal pushes you have power assist on, that checks if it is holding vacuum.

But that wouldn't explain the pedal travel.
You have air in the system or caliper(front) or slave(rear) has too much travel.

Rear is most likely, this can happen if you don't use the E-brake regularly or you don't back up and stop regularly, i.e. you park on the street all the time, no backing out or in to drive way.
Both of these cause Star wheel to open the shoes of rear brakes more to compensate for wear on the shoes.
Hold E-brake handle out and pump e-brake pedal a few times to see if it gets stiffer.

 

[AllanD]

On Rangers equipped with cruise control
have a brake pedal activated "vacuum dump valve"
to disengage the cruise control is the vacuum servo does not engage automatically