Bleeding brakes following master cylinder rebuild

Yeah, I know. I should have searched because there are bound to gazillions of threads on the topic of bleeding brakes. Call me lazy or maybe I just want to have my own thread :-)


Here it goes: I rebuild the master cylinder and I also replaced all brake lines with steel braided teflon lines. I am using a vacuum pump for bleeding.
So, to start out the mc was bone dry. I filled up the reservoir and started pumping but it seems like the air bubbles are never ending and I keep back filling the reservoir. I started at the front left (closest to the mc) and all of the other bleeder screws are closed.

How much brake fluid do I need to expect having to go through? Any other helpful hints? The manual for the vacuum pump talked about the process of bench bleeding the master cylinder....which of course I did not do.

Hi Torsten,

This is from the MGE library. Hope it helps.

Bleeding the hydraulic brake system

Before you start it is essential to top up the brake fluid in the master cylinder and ensure that the level is kept topped up, because if the level falls too low air will be pumped around the system.
Starting at the wheel furthest away from the master cylinder attach a length of clear plastic tubing to the bleed screw and feed the other end of the tube into a jam jar. You need clear tubing to be able to observe the air bubbles as they emerge from the bleed screw. It is helpful to buy a purpose designed bleed tube complete with a non-return valve.
Using the correct size spanner undo the bleed screw by half a turn. Then instruct your assistant in the driving seat to depress the brake pedal slowly and evenly. This pumping action should be repeated pausing between each stoke while you observe the fluid coming through. When the fluid is free of air bubbles, instruct your assistant to fully depress the brake pedal while you tighten the bleed screw.
Move on to the next rear wheel cylinder and repeat the process. Working your way all around the car, bleed each cylinder and calliper in turn. Once all the air has been successfully expelled the brake pedal should be firm with very little travel and no feeling of sponginess.

Should have bench bled it but all is not lost. With fluid in the reservoir, have someone pump a couple times and hold. Loosen one fitting slightly at the MC and close. Do it again till you have fluid. Do the other fitting the same way. Now you can go on to normal bleed procedure at each wheel.
Protect from inevitable drips and flush thoroughly with water when they occur.
RS

If you are using a vacum bleeder you may have a air leak somewhere is the system.. Make sure all bleeders are tight.
I would suggest that you get a helper and revert to the pump hold,release,pump hold and release. This way you may find you loose bleeder or leak..
Even better use a ezi bleed system that pumps fluid through the mc to the cylinders.

I just replaced my brake master cylinder with a new one along with some hoses
without bench bleeding. It was a piece-of-cake with one person,
a bottle, a plastic tube and some spanners.

Now, there's a different story about bleeding the clutch master cylinder, it took me weeks!

YOU REBUILT THE MASTER?

How does one go about bench bleeding and not make a mess when connecting the hardlines to the MC once it's installed?

Torsten: Didn't mean to hijack your post, but figured it was a related topic.

Paul

Paul,
I bench bleed the master by inserting a screw of the proper size in a short (3/8" long) piece of vacuum hose of the proper size to plug the fitting holes in the master. This allows me some time to install it without making too much of a mess. I also put down some paper towels under the fittings area to catch some brake fluid. Before pumping I open each wheel cylinder and let them drip for a bit being careful not to let the master run dry. Lastly I pump it up, bleed and wait 20 seconds before pumping again and I pump slowly. This lets the bubbles settle out and reduces frothing that happens from rapid pumping. The whole process is very quick and easy.

Alright, I got it all worked out.

I ditched the vacuum pump and had the wife pump the paddle. For some reason the vacuum pump manual was suggesting starting with the caliper closest to the master cylinder. I disregarded that advice and followed the conventional approach by starting with the brake in the opposite corner.

Thanks for helping out.