'67 MASTER BRAKE CYLINDER BLEEDING

[Craig S.]

Re: '67 MASTER BRAKE CYLINDER BLEEDING

Rob - I would pull the lines and rebleed with the bleeder tubes. Usually I do this in a vise first, befor it is in the car, but it may work OK in the car. Personally, I have had better luck with pressure bleeding or vacuum bleeding than gravity, but I realize gravity does work over time. I have one of the bleeder guns from Phoenix Systems......see link below.....Craig




Phoenix Systems Brake Bleeders

[Terry M.]

Re: '67 MASTER BRAKE CYLINDER BLEEDING

Rob,
I have a hunch that so long as there is air in the master cylinder (in this case in the rear), you will not get enough force on the fluid to begin the gravity bleeding process. As messy as it is, I think you will need to bleed the master cylinder again.
Does it not have bleeder screws on the master cylinder? Maybe opening the rear master cylinder bleeder screw will purge some air from the master cylinder. It's worth a try before going through the whole master cylinder bleeding process over again. Be sure to protect the finishes in the engine compartment from the brake fluid.

[Harmon C.]

Re: '67 MASTER BRAKE CYLINDER BLEEDING

Craig I now fill the lines from a bottle with clear tubing hanging from the hood and hooked on the M/C line before I hook the lines to the M/C. I started doing this when gravity bleeding would not work. Rebuilt M/C are sleeved from the local auto parts store and may not be done the same as yours was.I can't tell you the why but hands on I know what I have found. Lyle

[Rob A.]

Re: '67 MASTER BRAKE CYLINDER BLEEDING

I bled the master cylinder, installed "speed bleeder" valves and using a vacuum pump can't get hardly any fluid out of the rear calipers. Can the proportioning valve be the problem? I'm running out of ideas. I had no problems when I first installed the system and bled it for the first time. After I try bleeding one of the rear valves, when I open the other I can hear a suction noise, as is the fluid(and air) is being pulled in. I tried filling the calipers with fluid using a suction buld, and when doing so the caliper pistons push the pads in, but when I release the pressure they come back out instead of remaining against the pads.

[Page C.]

Re: '67 MASTER BRAKE CYLINDER BLEEDING

Hi Rob,
The "proporting valve" is realy a distribution block on cars with split master cylinders. There is a valve inside that switches from its neutral position when there is an imbalance between the front and rear brake systems caused by a failure on one of the two systems to maintain pressure under braking. It should also switch a light on in the dash. Try bleeding the system to the block and closing the lines and mash on the brake petal to get the valve back in the neutral position.
Regards,
Page Campbell

[Mike McKown]

Re: '67 MASTER BRAKE CYLINDER BLEEDING

I suggested the distribution valve three or four days ago and their was no response. Open a line to the front brakes and stomp the pedal to center the valve and then see if you can bleed out of the rear.

[Rob A.]

Re: '67 MASTER BRAKE CYLINDER BLEEDING

I tried to relocate your initial regarding the valve, but couldn't find it under my initial posting. Thanks for responding again, I'll try it.

[Rob A.]

Re: '67 MASTER BRAKE CYLINDER BLEEDING

Mike,

If I understand the valve correctly, it closed off flow to the rear brake lines, where I have no pressure now. If I disconnect one of the front lines and depress or pump the brake pedal, it will sense no pressure in the front line and shift to allow flow to the rear?

[Mike McKown]

That's the way they work. *NM*

[Rob A.]

Re: '67 MASTER BRAKE CYLINDER BLEEDING

Here's the latest. I removed the proportioning valve and it is in the nuetral position, clear in both front and back linees. I shot compressed air through the rear brake line and it forced the pads against the discs, so I know the line(s) are clear. That leaves the master cylinder. Maybe I'm not bleeding it correctly, or enough. Can someone go over the best way to bleed the master cylinder? Right now it is mounted to the brake booster with no lines connected.

[Joe R.]

Re: '67 MASTER BRAKE CYLINDER BLEEDING

Hi Rob:

I thought I would join this discussion because right now I am having trouble bleeding my 67 system and I, too, am looking for ideas. My system has all new calipers, hoses, and brake lines. The master cylinder was re-sleeved by White Post. The only component that I did NOT replace was the "distribution block." Right now the car is drivable but the pedal is a bit squishy and the pedal effort seems high (no power brakes). I have two questions/comments that perhaps some of the experts on the tech board can address.

1) I know that the main purpose of the moving parts in the distribution block is to turn on a switch when there is a pressure differential between the front and rear systems. Some people say that another function of this arrangement is to shut off the circuit (front or rear) that has low pressure. While this additional function may be included in newer designs, can anyone confirm with certainty whether the 1967 distribution block does this? If so, it seems like a valve that is stuck in one position could effectively disable the front or rear brakes.

2) I don't fully understand the operation of the dual master used on the 1967, but the drawings imply that it relies on a solid "slug" of brake fluid to effectively couple the front piston to the rear piston. If so, how does the bleeding process ensure that there is no air in this middle chamber, which is not explicitly part of eitherthe front or rear circuit? I suspect that there may be some air in this chamber in my master cylinder.

[Rob A.]

Re: '67 MASTER BRAKE CYLINDER BLEEDING

Well, the problem is fixed, brakes are bled and the pedal fine. The fix is embarassing, but....When I got the master cylinder from the rebuilder, it had a rubber boot on where it meets the brake booster. I told him it did not belong there and was not on when I removed it. He INSISTED it needed to stay on. When I removed the master cylinder and took it to a rebuild shop, I was immediatly shown how the seal was being smashed against the booster and not allowing the master cylinder from operating it's full stroke and pushing enough fluid into the lines. He said it belonged only on non-power brake installations. Thanks for all the responses.(as usual installer error turned out to be the problem)