Air in my master cylinder

I bench bled my new MC with plugs per the manufacturer's instructions, installed it in the Jeep and bled the brakes. Of course I had several leaks and at some point, the reservoir for the rear went empty.

I've read all the brake threads on and I'm sure I have air in the master cylinder. I'm sure it's not coming out now because the MC is not level. I really, really don't want to pull the MC back off to bench bleed it. I read about bleeding it in the Jeep, which sounds a lot better. I think I can get the MC level by taking the front tires off and lowering the front end (the back is already jacked up).

My question...
When the MC is level, why won't the air just be forced down the lines to the calipers to be bled out there? Why is it different than bleeding it back into the reservoir or into a container?

Thanks!
Billy

Level the M/Cyl, then use a pressure bleeder if you have one. It forces fluid under pressure into the M/Cyl, and you release pressure at the wheels (to let the fluid and crud - and air! - get forced out.)

You can try vacuum bleeding the thing, but it's still a bit dicey. I'd probably Dx the lines at the M/Cyl, then vacuum bleed it using fittings on the ports, then reconnect the lines and go from there. At least you won't be pulling the thing all the way off and remounting it...

5-90 said:

Level the M/Cyl, then use a pressure bleeder if you have one. It forces fluid under pressure into the M/Cyl, and you release pressure at the wheels (to let the fluid and crud - and air! - get forced out.)

You can try vacuum bleeding the thing, but it's still a bit dicey. I'd probably Dx the lines at the M/Cyl, then vacuum bleed it using fittings on the ports, then reconnect the lines and go from there. At least you won't be pulling the thing all the way off and remounting it...

Click to expand...

I forgot to mention that I've got speed bleeders, in case that makes a difference.

I tried the $30 vacuum bleeder from VatoZone, but decided it did more harm than good and returned it. I don't have a pressure bleeder, unfortunately.

Should I try to level it and bleed at the calipers or is that a waste of time?

Thanks!
Billy

JeepFreak21 said:

I forgot to mention that I've got speed bleeders, in case that makes a difference.

I tried the $30 vacuum bleeder from VatoZone, but decided it did more harm than good and returned it. I don't have a pressure bleeder, unfortunately.

Should I try to level it and bleed at the calipers or is that a waste of time?

Thanks!
Billy

Click to expand...

Level it, yet. I'm inclined to say that bleeding at the calipers is a waste of time tho - you'll have a hard time getting the rest of the air bubble out of the M/Cyl body. At least undo the lines and bleed from the M/Cyl body first. Once you get all of the air bubbles out of there, you can then move on to the wheels.

Bench bleeding a master cylinder is something that's just got to be done correctly, or it's going to screw up the rest of the job.

There's really nothing wrong with a vacuum bleed, done properly. But, I doubt that speed bleeders at the wheels (while a very good idea) will be any help when trying to get the rest of the air out of the master cylinder - work at the cylinder directly for that little headache...

Try this for bench bleeding in the car. I went to the junkyard and took the tubing from the MC to the dist. block. Undo the dist. block, undo your two lines, hook up your 'new' ones, upside down, gently bending them back into the reservoir, making sure the ends are submersed in the fluid. Gently cycle the pedal until the bubbles stop. I know how frustrating this is, last year three MCs in my '96 till I has happy, this year my son's '96, two MCs, still chasing a mushy pedal. Let me know if this works OK for you...Ray

How 'bout pumping the pedal a few times, then on the last pump, have that person hold the pedal down while you open the lines at the master? Once the pedal goes down, keep it down, close the lines. Repeat. :dunno: Almost like a pressure bleeder. When you pump it, you're building up pressure. Just don't pump too fast.

Hope that helps.

Thanks guys. I worked on it tonight and decided that my pushrod is not providing full stroke to my master cylinder. I'm going to pull it apart tomorrow and adjust the pushrod. While I have it apart, I'll probably bench bleed the MC again.

Billy