Well this has also been an issue for the 92 Dodge B350 5.2L. If am wondering why the pedal is so soft and the brake light comes on intermittently. Are the brakes controlled by the vacuum pump or off the manifold vacuum? The reseviors are full on the master cylinder and there are not brake line leaks. I am just really learning about this vehicle and appreciate the help I have recieved from this sites participants thus far. Thank you!

 

The brake light on the dash illuminates when the proportioning valve senses more movement in the front or back lines.

Usually this is caused by the star adjusters in the rear brake drum not self adjusting as designed.
How far does the parking brake go down before it works well?

The misadjusted start adjusters can also cause the pedal to go further to the floor, but a mushy pedal is usually caused by air in the lines, or perhaps a failing Master cylinder. A MC which whose seals are failing internally can also trigger a brake light as one piston pushes more fluid than the other.

They say brake fluid should be flushed out every 2 years as it absorbs moisture, and if then the brakes get hot, they can boil the water inside the lines, which causes Air bubbles and a mushy pedal and poorer braking.

A failing brake booster can cause a vacuum leak which can make the engine run poorly, and cause a hard pedal with much less power assist. It will not cause the brake light to illuminate.

 

Thanks landyacht318,

The parking brake works well about 1/2 way depressed (checked it tonight). The pedal is mushy and goes to the floor and the light comes on. If I "pump" the pedal the it builds pressure and the light goes off till the next time I use the brakes...with that said, I have had this van for over 10 years w/o ever changing the MC but I did change the fluid this last summer (sucked some out of the MC and replaced, drove a bit and repeated). The MC looks very rusty on the outside and maybe its just do for replacement too..

 

The MC does not circulate the fluid. Replacing the fluid in the MC is a good idea before bleeding the brakes, but does next to nothing if the brakes are not bled. The fluid right next to the brakes remains there until the brakes are bled. It is the fluid closest to the brakes themselves which sees the highest temperatures.

Pumping the brakes to build up the pedal is a sign something is wrong. The MC could be failing. If you do not have the confidence to take this on yourself, you will need to pay someone else to take it on, because one of these days you are going to push down the brake and it is going to hit the floor, repeatedly.

It's not just yourself that is in danger when this occurs.

MC's are pretty cheap, replacing them is pretty easy, the hardest part is bench bleeding them. Do not Buy a re manufactured one. A new one is only 15$ more, if that.

If you have any dirt roads in the area, drive about 15 mph and slam the parking brake down. If only one wheel locks, investigate the other wheel. If both lock, then replace the MC.

There could be other issues, but the start adjusters in the rear drums and the MC are the likely culprits in your symptom description.

If, when you replaced the fluid within the MC, you pressed the brakes there is a chance you introduced air into the system, and then just bleeding the brakes might fix the issue, but it would have happened immediately.

 

If no fluid is missing from the master cylinder and you have not been needing to add some during this time then replace the the master cylinder for it has an internal bypass which is why your pedal is traveling further than normal.

Personally I have found it easier to bleed the unit on the vehicle verses a bench vise. But to do that you need a second helper even if you use those little bleeder kits that come with some of the units. If you have the kit have the helper push the pedal to the floor and hold it until you have the hoses covered with your fingers, then have them slowly release the pedal. Now keeping the hose ends under the fluid level have the push the pedal again and hold it, again hold the end of the hoses closed and repeat. Do this till no air is coming up out of the fluid. Then slowly attach the brake lines and if all goes well you have brakes right from the start. But even so it is still best to finish bleeding the entire brake system so it has all new fresh fluid.

 

Good advise here too, BUT remember to bleed the lines starting with the REAR lines first and then the front.

QUESTION ... When braking, does the van pull to one side or the other? If so, air could be in the lines OR the rubber brake hose has failed causing it to bulge when the pedal is pushed as the engine is running.

 

I recently replaced my MC. The new one did not come with a bleeder kit, but it did come with plastic plugs for the output lines. I drilled holes and shoehorned in some clear plastic line into them. I pushed the piston a couple dozen times until I saw no more bubbles, left it in the vice and went to change my flexible brake lines.

Every time I walked back to the vice, I pressed the piston again, and kept getting small bubbles. I wound up breaking a steel line, so the MC sat overnight in the vice, and the next day, guess what, a couple more bubbles.

Without the clear tubing I doubt they would have been visible. When holding the piston in, I would wait for the bubbles to rise in the line through the fluid, so they did not get sucked back into the MC.

On my Van, the driver's side rear line is the furthest away from the master cylinder in terms of brake line length.

I never tried bleeding the MC on the vehicle before. I do remember insufficiently bench bleeding the previous MC, and it took forever to purge the bubbles from the lines.

 

Thanks for the replies all. This is why I use this forum....to get "informed". I am thinking I will have a mechanic change out the MC on the old van and hopefully that resolves the issue.

Good point about the fluid change and not getting the fluid out of the calipers. Next time I change the fluid I will be sure to bleed all the brakes too ( which will be done with this job I suppose).

I did put all new brakes (rotors, drums, calipers, and pads on this van about 1 year ago), and have not experienced any pulling right or left.

Thanks again all for the help.