Brake Bleeding w/vacuum pump

[Malones99]

As the title suggests, I am going to bleed my brakes this weekend. I bought a vacuum pump, since it will just be me. My question is when I bleed the brakes does the brake pedal need to be pressed to the floor or can it be in the "up" position.

To me I would think it has to be pressed down to "open" the master cylinder. Thanks in advance.

 

[corvhoe7795]

You want to leave the pedal up (not depressed). Think about it (like I just did), fluid is in all the brake lines, calipers and wheel cylinders. All this fluid condences when you push on the brake pedal, along with some from the master going into the lines. With the brake pedal up, all the fluid is relaxed. Soooo, leave your brake pedal alone when you're bleeding the brakes.

 

[Malones99]

Ok totally confused! Isn't the point of bleeding the brakes is to get the air out, hence replacing the air with fluid.

Please tell me if i'm wrong, if the pedal is up than no fluid can be drawn into the lines, or can it?

If the pedal is depressed, doesn't that open the valve in the master cylinder?

 

[brielly]

The fluid will flow just fine with the pedal up. Your vac pump will pull it through the lines. Make sure you keep an eye on the MC so it doesn't get too low or you'll be suckin in air.

 

[NYrr496]

It'll work fine with the pedal up.

 

[79powerwagon]

Ok totally confused! Isn't the point of bleeding the brakes is to get the air out, hence replacing the air with fluid.

Please tell me if i'm wrong, if the pedal is up than no fluid can be drawn into the lines, or can it?

If the pedal is depressed, doesn't that open the valve in the master cylinder?

You are not understanding the concept. Fluid in the master cylinder is ALWAYS forward of the piston, and will always be forward of the piston, no matter where the pedal position is. The amount of fluid never changes, just it's location and pressure.

Think of holding a balloon in your hand. Now squeeze that balloon. The balloon changes it's shape, and the pressure inside changes, but the AMOUNT of air inside the balloon hasn't changed one bit. Same thing with your brake system.

Get it?:yesnod:

 

[Malones99]

Go it! I now understand! I didn't think the fluid was always forward of the piston! duh, makes perfect sense!

 

[79powerwagon]

Good deal! Start bleeding away!

 

[79powerwagon]

Oh yes, start at the passenger rear, then drivers rear, then passenger front, then drivers front, no other order than this. It may take a good 15 minutes each, and don't let your reservoir run empty.

Have at it!

 

[peterey2]

tell yer neighboors to shut up when they yell at you for tellin yer buddy to "pump...hold....pump....hold" lol
ahh, good time!