Brake pedal soft only with engine running

[danman6677]

what about a flashing brake warning light after replacing shoes and such, how do i reset it or just pull fuse?

 

[duanes7]

As for fluid movement in the master cylinder, this is normal. With the cap off it will spray out everywhere.

My service manual doesn't mention anything about a flashing brake light, just on continuously or inoperative. The only thing I think that is supposed to make it flash is if the jumper wire is installed and it is flashing the codes (or is the for the abs light?) When does it flash? Does it come on when the truck is started and then go off after 3 seconds (bulb test) or so? If you don't touch the pedal does it flash on it's own or will it stay off until you hit the pedal or something? Is it flashing regularly or or just intermittently? On mine I could just tap the brake pedal and the light would go out.

How did you spread the calipers to make room for the new shoes? I've read that in the chevy's you should open the bleeder valve and let the pressure out there when pushing the calipers open, supposedly the backwards pressure can damage the abs. But I've never done that in any of my other vehicles.

What are the and such?

Are you sure it's not just still air in the system? How does the pedal feel? How is the braking power?

There are several things that are supposed to make the brake light come on.

Since yours isn't inop, I will write the on continuously brake warning system diagnosis routine. Mine wasn't really on continuously either, just came on when the pedal was pushed. Not exactly the fail you are getting, but may give you some info of where else to check for problems.

Step1: Disconnect park brake switch connector (left floor board above the parking brake pedal). Turn ignition to run. Check that the parking brake is released. In my case I also performed whatever it was that made the light come on (pushed pedal nearly to the floor).
Result1: Light turns off.
Action 1: Check for adjustment of parking brake switch or replace if adjustment is ok.
Result 2: Light stays on.
Action 2: Go to step 2.
Step2: Disconnect brake pressure warning switch connector (2 wire connector on rear of EBCM).
Result 1: Light turns off.
Action 1: Diagnose brake system (this was my fail and it was due to air, still).
Result 2: Light stays on.
Action 2: Go to step 3.
Step 3: Disconnect EBCM connector c1 (the big rectangular one with 7-8 wires in it).
Result 1: Light turns off.
Action 1: Diagnose ABS.
Result 2: Light stays on.
Action 2: Go to step 4.
Step 4: Disconnect daytime running lights module connector (buried inside dash to the left of the steering column in front of the cross bar).
Result 1: Light turns off.
Action 1: Go to step 5.
Result 2: Light stays on.
Action 2: Locate and repair tan/wht wire (33) for short to ground between DRL module and instrument cluster.
Step 5: Turn ignition to off. Connect self powered test light from the cavity A of the drl module to ground.
Result 1: Test lamp lights.
Action 1: Locate and repair the lt blu (1134) wire for a short to ground between the drl module and the park brake warning switch.
Result 2: Test lamp does not light.
Action 2: Go to step 6.
Step 6: Connect self powered test light from the cavity F of DRL module to ground.
Result 1: Test lamp lights.
Action 1: Locate and repair the tan/wht wire (33) for a short to ground between the DRL module and diode 1 or the PPL (680) wire for short to ground between diode 1 and the ECBM or brake pressure warning switch.
Result 2: Test lamp does not light.
Action 2: Locate and repair the lt blu wire (1134) for short to ground between the ignition switch and the DRL module. If not short is found, replace the ignition switch.

 

[danman6677]

Well i reset the abs and no light is on but the soft pedal is pissing me off. I press the brake and it will be soft and I stop but I can pump them up and the pressure builds and stays firm until i release it and start driving again. I bled it and bled it but not sure if i should change the MC or what.

 

[twomanymontes]

Danman6677, The red brake light will come on if the pressure between the front and rear is not equal. the proportioning valve will float side to side and trigger the light. If the pedal feels low, but will pump up, then it sounds like the rear brakes are way out of adjustment. There is too much travel in the rear brakes before contacting the drums. I always adjust them till there is just a little drag on the wheels. Too much will cause a vibration and over heat the brakes. If you can spin the wheel 1 rotation after releasing your hand, your pretty good.

As for the Master Cylinder, if it's leaking or your pedal will fade while at a stop, then change it. Otherwise it's doing it's job.

Once you have the brakes adjusted, try bleeding it again.

 

[twomanymontes]

Glad your brake issue was a simple repair. I have seen quite a few vehicles come into the shop with things worse than the calipers mounted wrong. Ever see a vacuum hose and clamps on a brake line? They balloon up like a frog, LOL!

How did you spread the calipers to make room for the new shoes? I've read that in the chevy's you should open the bleeder valve and let the pressure out there when pushing the calipers open, supposedly the backwards pressure can damage the abs. But I've never done that in any of my other vehicles.

The reason behind that is any moisture or dirt that has accumulated in the caliper piston bore won't be pushed back into the ABS unit where the dirt can tear the seals or jamb up the solenoids.

 

[danman6677]

ive always just used a 1x4 and a c=clamp

 

[duanes7]

"The reason behind that is any moisture or dirt that has accumulated in the caliper piston bore won't be pushed back into the ABS unit where the dirt can tear the seals or jamb up the solenoids."

That makes sense.

I went thru the diagnosis and unplugging the brake pressure switch is what was causing my brake light to stay off. My pressure diff was caused by air in the front brakes. But the backs being out of adjustment could have easily caused it too.

Did your brakes work before you replaced the "shoes and such"? If so, then I would stray too far from what you did.

To adjust my back brakes I first installed the drum, removed it adjusted the star wheel a couple of teeth and repeated this until I could feel resistance with the drum going on. Then I back the wheel off a few teeth and installed the drum and wheel. Then I pulled the metal clip/cover off the inside, bottom, center of the rear drum backing plate. Took a straight slot screwdriver and clicked the star wheel a couple of teeth and spun the wheel til it barely began to drag.

 

[low4x4]

also had the same problem after intalling a master...and at the end of the directions it said if the pedal is still soft after installation further actions are required...by backing up and pressing the brake pedal multiable times, you self ajust the rear brakes, as long as the adjusters are working correctly...i did this 5 or 6 times and the brakes are 10 times better and don't go to the floor with the truck running