Horrible brake sounds while pressing the pedal

[firemedicsafd]

I just got frankenblazer back on the road after 1 ton axle swap. Converted the rear from drum to disc. Then bled the brake lines...4 times. Vacuum booster and factory master cylinder. It makes a horrible whining sound when the pedal is pushed until the brakes start grabbing then it goes away. It does it every time sometimes louder than others. Please help me!i am. EAGER to get this thing on the road full time. As always, you folks come thru when needed. I'm needing another miracle from the peanut gallery!

I forgot to add, the sound is equilivent to a power steering pump without fluid turning. But it is not regular sounding. It varies in pitch and time of sound.

 

[Snoozer]

Just brainstorming here:

• Did you replace the vacuum booster and/or the master cylinder?

• Sounds silly, but did you install the brake pads correctly (I've seen guys accidentally put them on "backwards").

• Check the vacuum line going from the booster to the intake manifold. Make sure its not rotted/cracked, or loose fitting.

 

[firemedicsafd]

Just brainstorming here:

• Did you replace the vacuum booster and/or the master cylinder?

• Sounds silly, but did you install the brake pads correctly (I've seen guys accidentally put them on "backwards").

• Check the vacuum line going from the booster to the intake manifold. Make sure its not rotted/cracked, or loose fitting.

MC got replaced a while ago but sat right after install. VB has not been replaced. I have HYD boost system getting ready to go in but I wanted to get it moving before doing more work that takes it out of commission. Vac line is new.

 

[Snoozer]

You bench bled that new master, I assume?

It wouldn't quite explain the "pump whine" sound. But process of elimination helps when troubleshooting. Plus, maybe it will spark a suggestion from other members.

 

[Big Ray]

...fluid level...?

+1 on backwards pad...

brake pad "chatter"...the pad vibrates until enough clamping force makes it stop...?

Glazed pads...? just went through this one myself.

 

[firemedicsafd]

I did hook the MC to a vise and push the plunger all the way in several times. Maybe I don't KNOW bench bleeding procedure. Please enlighten me on that one. Can the surface rust from rotors cause glazing? Or that brake chatter? It did sound better today ( not as much noise) when I ran it around the block. Another question related to brakes. Why does the brake light come on near the bottom of pedal travel? Then go off when pedal is released? Guess I should have included those symptoms in the original post huh. Thanks!

 

[Big Ray]

IDK...

When you went with disc did you change the MC? I believe you need a larger MC with disc.

If you didn't I think you are setting the proportioning valve to think the brakes are failing.

Not positive, just my best guesstimate without further research...

 

[firemedicsafd]

Do you folks think I should do the hydraulic conversion to see if the problems clear up? Do I need and adjustable prop valve now that I have disc in the rear?