Hey everybody, I posted about this on another dodge forum and got a good amount of help but would like a second set of minds to help me work this one out.

So here is my story/situation,

About a week ago when braking I started hearing a hissing coming from my brake booster, A few days after that the "E-Brake/Park brake" light would come on only when the brakes were pushed down at a dead stop, Then a day or two after that it progressed to having the brake light on constant and drastically reduced brake power.

That all leads to me today, I decided since my master cylinder and brake booster were pretty rotted (Master Cylinder must have been leaking, Not sure as I bought the truck less than 2 months ago.)

So I took the few hours and replaced everything and made sure it was all installed correctly, Although I didn't not mess with the adjustment of the booster linkage (If that makes sense.) I just measured it to the same length as the old one and adjusted them to the same length.

After the install, I bled the master cylinder, Then connected my brake lines and filled the reservoir up to about 3/4 full. I then bled my front brakes until a decent stream of fluid was coming out with no air bubbles. Unfortunately I was unable to bleed my rear brakes as the bleeders are seized and to not risk rounding them off to extreme I'm going to wait until I can bring my propane torch home from work to loosen them up.

So now to the test drive, On first impression to my disappointment the brakes still had a lack of power behind them, and the brake light would light up every time the pedal was pressed down. However, If I were slowing down and pumping the brakes the brake light would only come on during the first pump and then go off after that, And after the first pump or two the brakes will firm up and feel like they should.

After the test drive I decided to put it in the garage until I can figure out my situation a little more...

So has anyone ever encountered this or can add some information? I just want to know how to make my brakes stiff again and why my brake light is illuminated in harmony with the brakes getting soft while being pressed.

Any input would be greatly appreciated!

Thanks,
Alex

 

Other than the parking brake being set, the brake light only illuminates when there is a loss of vacuum. IIRC, it comes on around 8in-Mg. Sounds to me like there's still a leak in the system.

 

Alright, I just ran out to the garage to check my main hoses. As it turns out, The main vacuum hose coming from the pump was worn through the insulation and the hose was slightly worn down to where you can see the threads, Would this small tear cause that much loss of vacuum..?

 

It's a possibility. Only one way to find out and at least it's an easy task. Just something else to try and eliminate from the other possible causes.

 

You can't get a good pedal until you bleed the rear.

The vacuum sensor is on the inner fender drivers side near the hood hinge, check that hose and connection out.

 

Our trucks have a combination valve mounted on the frame rail below the master cylinder and one of its functions is to monitor and alert you if there is any differential in pressure between front to rear as would occur in a hydraulic system failure.

Due to the fact your rear brakes probably have a small amount of air in the system that you have not yet been able to purge the valve it working as it should.
Step on the brake and you are pushing fluid against air.

As soon as you are able to bleed the rear brakes the light should stay off,

Note, if you step on the brake hard and the light stays on afterwards you might have to reset the valve.

Read below about the Pressure Differential Switch and Valve





This was a common phenomenon on GM products of the 80's and 90's.

Jim

 

If you disconnect the wire to the proportioning valve and the light goes out, that's the problem.

Bleed back brakes. Nothing else will help till then.

 

Might also be a sign of rear brakes needing adjusting.

 

Just a little update, I got the rear brakes bled and now the truck stops like a million bucks. Thanks for the help everyone!