Bench bleeding 66 master cylinder, need assistance

[Nick M.]

I am in the garage bleeding my resleeved 66 Master cylinder and just wanted to know if what I am experiencing is normal, before installing on the car.

installed all new seals, springs etc.
bore was resleeved by Whitepost
everything clean
lots of brake fluid to lube
reassembled everything according to manual
set up brake bleeding two lines on in each compartment, submerged in brake fluid

when I push the m/c piston in, I get lots of pressure from the rear compartment shooting in the air out of the larger hole and air bubbles out of the rearward smaller hole
The Front compartment show very little action and only when you push the piston all the way in
I pulled out the hose from the Front compartment above the fluid line and near the end of the stroke do I get fluid coming out of it

unlike the rear where I get a steady flow throughout the stroke

first time doing this, so any comments would be welcome

[Monte M.]

Re: Bench bleeding 66 master cylinder, need assistance

Nick,
Remember that the master cylinder reservoirs are typically swapped. The one closest to the firewall is in the rear, but it operates the front brakes. It will not do anything to the rear brakes until the plunger is at least 1/2 way or more into the cylinder.

If by chance the bench bleed did not work, you can bleed it with a small straw on the car. My guess is the front brakes are working fine. The rear reservoir. You can do this on the bench as well.

1. Take a straw and cut it in a piece between four and six inches. Whatever works for you.
2. Loosen the brake line that goes to that reservoir. The one that is not working.
3. Put a rag under it as you will have a little brake fluid trickle out of that fitting as this happens.
4. Now, look in the reservoir that is not working right and find the small hole in the bottom of it. Put about 3/4" +/- of fluid in that reservoir.
5. Place one end of the straw in/over the small hole at the bottom.
6. While a friend very slowly pushes the pedal to the floor, blow in the hole gently. Only when the pedal is in the correct place will you feel the fluid going in. Do not let the straw empty of fluid.
7. Do this a number of times until you see fluid coming out where the brake line attaches.
8. Tighten up the brake line fitting and clean it off.
9. Proceed with bleeding the brakes as normally would.

You can do the same thing on the bench if it is not in the car yet. I typically bleed the master while it is on the car because it is much easier and less messy this way.

Best of luck,

Let me know how it turns out.

Monte

EDIT is italics

[Nick M.]

Re: Bench bleeding 66 master cylinder, need assistance

Thanks Monte for the reply and instructions.

just to Clarify, are you saying that the brake line coming from the Rear of the car should be attached to the front cavity of the the master cylinder and the Front line should be attached to the Rear cavity?

The pressure to the front cavity only comes on when I push the piston in about half way, but doesn't have as much pressure coming throw it as the rear to the end of the ststrokes appreciate all the help

[Jim T.]

Re: Bench bleeding 66 master cylinder, need assistance

From reading my Corvette Shop manuals for 63-64 supplement, 1970, and 1971 I do not remember which book mentioned in bleeding the master cylinder off the car, bleed once with the master cylinder tilted down in the front and them tilt the rear of the master cylinder down and bleed again.

[Monte M.]

Re: Bench bleeding 66 master cylinder, need assistance

Nick,
I am sorry for writing something very confusing. I actually wrote it backwards/wrong. The rear most reservoir does service the rear brakes. As the front most reservoir services the front brakes. I should have been focused on the whole project, not just the bleeding.

As Jim says, doing it by the books works great. I am just throwing this method out there in case you get stuck.

Again, best of luck

[Nick M.]

Re: Bench bleeding 66 master cylinder, need assistance

Gentlemen, thank you for all the help

i bench bled the M/C
installed
used my new motive bleeder.....love it
Firm peddle, works great, thanks for the great advise

regards