Brake Are Almost None Existent : Can't Stop Won't Stop

[campbmic]

I've owned an 03 Yukon XL 130k for about 2 years now. I've only driven it about twice a year. When I got it the brakes seemed REALLY soft. I'd have to drive very slow and be extra cautious, so it mainly just sat in my garage.

I thought it was the front brake pads. Today I took the front driver tire off and the brake pads look like they have TONS left. The master cylinder is also full (the liquid is black. should it be?).

Today I bled the front two calipers. When I opened the valve the liquid came out clear, but no air or anything. I also noticed with the car off the brakes seem to get firm and feel like they're good. Then when I turn the car on the pedal becomes soft again.

The words "service brake" have appeared on the in-dash display since I've owned it. The ABS light and brake light are not on. They also don't come on when the car has the key turned to accessories so I think they may just be out.

Can you guys help me to figure out what the problem is?

Pics: http://imgur.com/a/GKoPM

Sorry about the giant images

 

[sumo]

Your rotors! you need to replace them or have them resurfaced to start. all that corrosion is preventing your pads from making proper contact with the braking surface of the rotor. Also when replacing the rotors, you should take the pads out and sand the pad surfaces. Chances are the pads are glazed from trying to stop on those rotors. As far as the service brake, Chances are its related to the abs but you'll need to have that scanned. Did you happen to check the slide pins when you did your brakes? Frozen slide pins will also cause soft brake pedal or they can cause the pads not to release and cause excessive drag.

 

[Chip18]

Hmm ... I don't think you can just just bleed the front brakes and not end up with air in the system?? The pads don't look they are gone ...but they do like they are pretty close to the wear limit??

No ... the brake fluid should not be black ... it's pretty much shot at that point. For the record we just got our 2004 Denali and the brake fluid is "black also???" The brakes "appear to work fine thus far" but I don't like it, so I will be flushing it all soon.

But ... most likely your pads and or rotors are glazed, and you have "Air in the system" ... soft brake pedal. You could scuff up the rotors with 400 grit sandpaper, replace the pads and flush the system.

Use one of these ... :

http://www.jegs.com/i/Motive+Produc...LR59x0aE2j1R9B3m7FmKoyIXFG4gxL4CYtxoCPj3w_wcB

I'd jack up the rear ,higher than the front (nose down) and go right rear, left rear, right front left front, and you should be fine.

And use lubra Plate on all the Caliper Slider Bolt, in my experiance a sticker caliper slider bolt will dart ... quite "violently" to the side that sticks!! Not a load of fun!

 

[campbmic]

I'm not super familiar with the brake system but can change the pads/rotors out if thats the problem.

However, the brake pedal seems to stiffen up and be fine when the car is off. Then when the car is on the brake pedal becomes soft, when I press on it I hear a kind of "swoosh sound", and the pedal goes much further down to the floor. Wouldn't this point to something aside from the brake fluid/pads/rotors? Is there some "brake booster" that comes on when the car is on that could be at fault?

Not trying to argue as you guys obviously know more. I just want to make sure I include all the information before I start buying parts.

 

[mizzouguy]

I vote air in lines or master cylinder is shot. I'd probably start with a flush using the motive bleeder mentioned above by @Chip18 because black fluid is bad lol. Is it hydro-boost or vacuum?

 

[sumo]

You should really start with those rotors. Then grab a buddy and rebleed the system. Maybe you can have a local auto store scan that ans light for you

 

[campbmic]

I'm about to take it to get a free brake check.

Before I do. I'd like to get that black fluid out of the MC reservoir and bleed the brakes again. What's the best way to get the fluid out of the MC and replace with new fluid. I've heard there could be a "brake booster" or "ABS module" after the MC that I DO NOT want to get air into.

I figure replace the fluid in the MC then bleed rear passenger, rear driver, front passenger, front driver. In that order?

If that doesnt fix it then I'll take it for a brake check

 

[sumo]

Best way is to purchase a mighty vac. One man operation. Fill the res, open one of the bleeders and pump until res gets low. Close and repeat for other calipers. Ideally you're supposed to start with the farthest from res but I never had any problems starting from anywhere.