Hey guys,
here's the story.
A few days ago, I started noticing a terrible grinding noise in my drivers rear wheel. From the noise I knew the caliper had failed, bummer because I had just replaced all four pads and rotors last year. A few days later when I had time, I pulled the wheel off and took off the brake components. Just like I'd thought, the caliper failed, destroyed one side of the pads, and destroyed one side of the rotor.

I set out to replace everything. I got all the parts including the caliper taken off when I ran out of daylight. I wanted the caliper off so i could turn it in for the core when I picked up the new parts. Once dark came over the land, I left the car, leaving the left rear brake line hanging over a catch basin. I installed all the new parts yesterday and bled the brakes today, but only at that one new caliper. The brakes aren't tight though, so there must still be air in there.

The guy at advanced auto parts says that I have to bleed the other rear wheel and also the master cylinder and that even then I might still be screwed. I figured I'd check here before I followed his advice, because they've led me astray many times.

I do have an ABS scan tool, but the ABS is currently disabled because of a bad wheel speed sensor (think I can get a good used one at a junk yard?) so I'm not sure if it will be effective in helping. I'll use it tomorrow though and keep you updated.

Let me know what you think, what to bleed, that kind of thing.
Thanks,
~Dan

 

yeah start at the master and bleed that first. if the line went completely dry its possible air got into the other side. so bleed the other back side then if that dont fix it do the front. if you ever have tho leave the vehicle with a open brake line pinch the rubber hose so this doent happen again. shouldnt need any abs tool. just bleed them doing the pump and hold method

 

Leaving the line open drained fluid from the master cylinder allowing air to enter the ABS unit. Fill the master cylinder, open the caliper bleeder that you replaced and let the system gravity bleed until no air is present, DO NOT pump the pedal. Repeat this for each wheel making sure the master stays full the entire time. After gravity bleeding all 4 wheels, make sure the bleeders are closed. Use your ABS scan tool to perform the automated bleed. This is the ONLY way to remove air from the ABS unit. The automated bleed will move the air that's trapped in the ABS unit into the lines. Gravity bleed all 4 again until no bubbles exit the bleeder valves. Gravity bleed can take 10 or more minutes per wheel. After the second gravity bleed, have an assistant apply pressure to the brake pedal, pumping is not recommended or necessary. Bleed each wheel.... done.

 

Have never used a abs tool and have done lines and bled brakes on many s10s with no problems. But heck if you have the abs tool use it. Gravity bleeding doesn't work if there's no fluid to gravity out the rest.

 

If the master cylinder runs dry, air obviously will enter the ABS unit. Bleeding the system by pumping the service brake will not remove air that is trapped in the ABS unit. The automated bleed operates each solenoid and forces the trapped air into the lines. After the automated bleed completes, each wheel needs to be bled to expel the air.

 

The master cylinder never ran dry. The lowest the master cylinder got was inbetween the "fill" and "full" lines on the reservoir.

I'm confused now. Should I be gravity bleeding every caliper or just bleeding the master cylinder and the rear calipers?

I'm trying to find a walkthrough for bleeding the master cylinder but I'm not finding one that's making me confident to do the job. When I look at it, I think I understand how to do it, correct me if I'm wrong.

Remove master cylinder cap.
Attach hose from both brake line leads at the master cylinder
Run the hose back into bottom of the reservoir
press brakes until air is out of the system.
reattach brake lines.

Did I miss anything?
The part I'm confused with is that the way I'm looking at the master cylinder, it doesn't have bleeder screws that are separate from the lines. Rather, the lines and the bleeders seem to be one in the same. Therefore, how would i take off the brake lines, attach hose, bleed the system, and then remove the hose and reattach the brake lines without air re-entering the system?!

 

As long as the master cylinder didn't run dry, and you didn't loosen any of the brake lines, (other than the flex hose at the caliper that you replaced), the fix is simple. Remove the master cylinder cover & gasket, fill the master cylinder, leave the cover & gasket off, open the bleeder at the caliper that you replaced. Allow it to gravity bleed, (Don't pump the pedal) until the fluid comes out clear, (no bubbles). Shut the bleeder valve and have an assistant apply pressure to the brake pedal. Slightly open the bleeder and watch for air bubbles, close the bleeder before the brake pedal reaches the floor. Usually takes a couple of times, that's it. If bubbles are present, release the pedal, apply pressure and repeat until there are no air bubbles when you open the bleeder. If you opened any other bleeders or lines, repeat the process on each wheel that you opened, (gravity bleed first, then apply pressure on the pedal). Make sure the master remains full during the entire process.


If a line was loosened at the master cylinder or ABS unit, or the master ran dry, an air bubble was introduced into the ABS unit. When that happens, the automated bleed must be done.

You've got the right idea for bench bleeding the master cylinder. There are no bleeder valves on the master. The lines must be removed and new lines must be custom bent & installed to the outlet ports of the master that curl up and into the reservoir, below the fluid level. With the master held in a bench vise, fill the reservoir, then push the piston in slowly, until it stops, then slowly release the piston. When there are no more bubbles expelled from the lines when pushing the piston in, you're done. When the master is reinstalled, and the lines reconnected, the automated bleed must be done, along with bleeding at each wheel.

 

Here's an update.
I went to advanced today to get the stuff necessary to bleed the master cylinder. They said the method of using hoses to route back into the reservoir isn't applicable to my 2000 jimmy model master cylinder, because it doesn't have bleed screws. I was told to get two caps the same size as the lines, take off the lines, put the caps on, and just push in the pedal which would make any air bubble up.

I followed that procedure and no noticeable amount of air came up.

Then I bled the driver rear brake, the one that I initially did all the work on. I would have done the passenger rear, but the bleed screw on that caliper is a larger size and I didn't have hose that would fit it.

My pedal still goes almost all the way to the floor.

I will bleed the passenger rear brake tomorrow, but I can't imagine this much air would have gotten into those lines.

 

VERY FEW master cylinders have bleeder screws, in fact, I can't remember GM using them since the 80's. Those kids don't have a clue... Using flexible hoses or steel lines is exactly how you bench bleed the master. CAPS???? and push the pedal??? Think about it... when you push the piston in, fluid comes out... when you release it, air gets sucked back in. That's why you need to keep the hoses/lines submerged in fluid in the reservoir. When you don't see any bubbles, you're done. Usually takes several full strokes to expel all of the air. It must be done in a vise... pushing the pedal will not give a full stroke in on the piston.

 

Well I am a Bus and Truck Mechanic and yes I agree that ABS systems should be bled only normally if one brake line for example is replaced ,if a brake line or rear lines for example is let run dry Air can get into the ABS Block and most certainly there are three methods too bleed not including normal and gravity fed and they are pressure bleed ,Vacuum Bleed and or using an ABS Electronic tool to bleed the system or systems
As far as Cars and trucks are concerned I have also had no problem using one of the three methods mentioned above ,I might be a newbie here but old in the tooth lol