72 master cylinder bleeding

[Matthew S.]

Hi Everyone,

I just finished rebuilding my calipers and master cylinder and replacing all the rubber brake hoses. My last step is to install the master cylinder and then bleed the brakes. I know that bench bleeding the master cylinder is usually recommended but my question is, can I install the master cylinder, fill it with fluid and then use my Mity-Vac on the master cylinder bleeder screws to bleed the master cylinder? I figure that way I have a much smaller chance of getting brake fluid all over everything. I looked through the archives but didn't see this particular question addressed.

Thanks for your help - Matt

[Gary Schisler]

Re: 72 master cylinder bleeding

The downside to doing it this way is that you risk getting brake fluid on your fender. You DO NOT want this to happen since brake fluid is an excellent paint remover. Even one drop on a fender for a second or two is enough to cause a blemish. I would rather get some brake fluid on my tools and bench than on my car.

What is wrong with bench bleeding? Two small sections of tubing, hooked up to the bleeders and inserted into the cups and bleed until no more bubbles. This is an easy and fairly quick task.

Gary

[Matthew S.]

Re: 72 master cylinder bleeding

Hi Gary,

Yes I know that regular brake fluid will destroy my paint, that's why I'd prefer not to have any in the master cylinder when I install it. The downside to bench bleeding that I see is that after I bleed the master cylinder I then have to move the master cylinder from the bench with brake fluid in it and attach it to the firewall and without spilling any of the brake fluid on anything. I'm not concerned about the bench or my tools. They've already been subjected to brake fluid when I rebuilt the calipers and master cylinder.

Perhaps I'm missing a step on bench bleeding though. After you've bled the master do you remove the bleeding tubes and install some sort of plug or do you leave the tubes in so the fluid won't leak out? If you use plugs and put the ap on the master cylinder then it would be sealed and no chance of fluid leaking out.

Matt

[Jim T.]

Re: 72 master cylinder bleeding

Bench bleeding the master cylinder with a the master cylinder mounted in a vise with the front of the master cylinder tilted towards the floor is a method recommended to remove any trapped air in the master cylinder. To prevent paint destruction accidents tape a large piece of plastic over the fender with a protective fender cover over that in case you drop a wrench on the fender. Don't let you master cylinder run dry getting your brake calipers bleed. Brake fluid is hydroscopic and absorbs moisture, open containers, open master cylinders allow this to occur. Some owners change out their fluid on a regular basis because of this.

[John H.]

Re: 72 master cylinder bleeding

Matt -

I use the setup in the photo (from the "Help" section at your FLAPS) to bench-bleed, put the cap on, then use a couple of rubber caps on the plastic fittings when it's ready to install. When bolted down, quickly unscrew the plastic fittings and attach the brake lines with a newspaper below to catch any drips.

[Matthew S.]

Thanks John - I'll try the setup you use *NM*