Bench Bleeding a Master Cylinder

[Mario Boni]

Hi, I've gone through the archives and read about replacing a master cylinder in a C-2. Many people recommend bench bleeding the master cylinder. I'm about to replace the master cylinder on my 1967 L79 non-power brake car. Can anyone describe step-by-step instructions on how to bleed the master cylinder. BTW, the 67 master cylinder has two bleeders on it. Thanks a lot.

[Tracy C.]

Re: Bench Bleeding a Master Cylinder

I just "Googled" your subject line and got SEVERAL hits on the topic. Nothing magic about a Corvette M/C. any of these should tell you what you need to know.

tc

[GL Anderson]

Re: Bench Bleeding a Master Cylinder

If you have the plastic fittings that screw into the side of the MC and the tubing and clip that goes with them you fill the MC with brake fluid and run the tubes one to each chamber if there are 2 chambers or into the single if it only has one, making sure the end(s)are under the fluid near the bottom of the cylinder then depress the end of the MC to push the air out thru the tube(s)and suck in the brake fluid until there are no more air bubbles. That is done on the bench in a vice or something to hold the MC. However I do it that way but bolt it on the car and hook up the rod and pedal then making sure there is a rag over the MC I pump the pedal many times very slowly to get the air out or have a helper do it and I watch. Have an open container of WATER handy in case you get a spill on the paint as brake fluid will mess up many types of paint. If you do get brake fluid on the paint then quickly pour water on the spilled spot and gently wipe dry after you are sure you have enough water run on it. Bleeding it on the bench is safer for the paint but it is a pain to do. Bleeding on the car is much easier but a risk to the paint if you get a splatter.

[Jim T.]

Re: Bench Bleeding a Master Cylinder

Only thing to add is what the service manual says, secure the master cylinder in a vise only tight enough to hold it with the front tilted slightly down. This helps with removing the captured air.

[Jim K.]

Re: Bench Bleeding a Master Cylinder

Last thing to add, most Auto Parts stores sell a MC bleeding kit with fittings and hoses for real short money ($10) I think it has similar instructions too...

[Joe L.]

Re: Bench Bleeding a Master Cylinder

GL-----

No worries about paint if you use DOT 5 silicone fluid.

[Mario Boni]

Re: Bench Bleeding a Master Cylinder

Thanks everyone.

[John H.]

Re: Bench Bleeding a Master Cylinder

Mario -

The bench-bleed setup looks like this.

[Mario Boni]

Thanks John

Just a couple more questions. I'm guessing I remove the plastic fittings and hoses once it's bench bled? Then I put the master cylinder cap on the master cylinder? Then I mount the master cylinder in the car? Do I lose a lot of fluid when I remove the plastic fittings and hoses? Also what are the bleeder valves for on the master cylinder? Thanks again.

[Jim T.]

Re: Thanks John

Mario when you remove your master cylinder from your car put rubber caps over the brake lines you disconnect from the master cylinder. After you bench bleed the master cylinder leave the plastic fittings and hoses on the master cylinder and relocate the hoses to install the cylinder cap on the brake master and install it on the car. When the master cylinder is mounted remove one plastic cap/hose and connect the brake line loose. Now remove the master cylinder fluid cap and let the fluid gravity feed into the loose brake line connection to displace air and then tighten. Then connect the other brake line loose and gravity bleed and tighten. Doing it this way you should not have any air in the brake lines you connect. With this out of the way you can replace the cylinder cap. With all the new fluid in the master cylinder you could use more new fluid and bleed all four brake calipers and remove the old fluid from them. It is generally recommended to replace/flush the brake fluid about every two years.

[Mario Boni]

All Done--Thanks

Thanks for all the replies. Here's a pic of the new master cylinder in place.