bleeding master cylinder

HI I have a 97non abs and I'm trying to bench bleed the master cylinder. So I put the Mc on the jeep and ran the rubber hoses from the brake lines back into the res and pumping the brake pedal but the air bubble never go away. It's it OK to have a few bubbles in the Mc
thanks nate

no bubbles.

vacuum bleeding works the best. If you have an air compressor the harbor freight vacuum bleeder works well for the 25 bucks.

Tap on the bottom of the mc to help free the bubbles. Pump and release the pedal very slowly. And make sure the rubber hoses and connectors are air tight. That's a common place for air to enter.

While in the car, the mc is tilted which makes it difficult to remove all the air. I've done the classic bench bleed, with the mc in a vice on a bench. I was able to remove all the air after about 50 pumps. I've read you can jack up the back to level the mc to help clear the air. But removing the mc isn't difficult, so I'd suggest doing the classic bleed. Wildwood makes a kit that makes the task easier. And be sure to use flare nut wrenches and be careful not to cross thread the nuts when getting them started.

Make sure all connections are tight so its not pulling air back in through a fitting.

This is how I did it, with the old prop valve hard lines as stubs

Talyn said:

Make sure all connections are tight so its not pulling air back in through a fitting.

Click to expand...

That was my first thought, tighten the bleeder hose fittings maybe. I've that sort of issue with bleeder valves on calipers, no matter what I had very tiny bubbles showing up, turned out to be air sucking in past the threads...

I used some Teflon tape on the plastic fittings that came with the Wilwood kit to keep them air tight.

i bench bleed, then bleed it at the master on the vehicle by pumping up the pedal and cracking the lines at the master. only way ive been able to get it to fully bleed without a pressure setup.

As Ehall and Grimm note, the only way I've ever found to do this is to bleed the MC itself. You can do this after it's mounted if it's too late to bench bleed with Ehall's rig which is the way you're supposed to do it. Put some pressure (or have an assistant put some pressure) on the pedal, pump it up and then briefly crack the connections on the MC. Make sure they're tightened before the pedal is allowed back up.

One of the handiest home made tools I've ever made was simply to take a longish tailgate strut from some unknown source, and mount a wooden block on the cylinder end, with a rounded notch in it. The rod end of the strut is pushed against the brake pedal, and the block under the steering wheel, providing an un-manned push on the pedal. I've used that as a one-man brake bleeder for many years. You have to go up and down a few times, but it works at any time of day or night and does not eat or drink beer.