Split braking system issue

[40cpe]

My '55 Victoria has power disc/drum brakes installed by a previous owner of the car. Recently while driving I noticed the brake pedal was soft and loosing pedal height. I was local, so I drove it home to check the brake fluid and leaks. When opening the reservoir, I noticed brake fluid on the brake warning switch and on the distribution valve and inner fender. The reservoir was empty. I replaced the switch and refilled the reservoir. Now the brake pedal is at normal height and firm. I drove the car yesterday and noticed that increasing brake pedal pressure doesn't increase braking. I wonder if my split system is activated and how to reset it. Thanks for advice you might have.

[KULTULZ]

The reservoir was empty. I replaced the switch and refilled the reservoir. Now the brake pedal is at normal height and firm. I drove the car yesterday and noticed that increasing brake pedal pressure doesn't increase braking. I wonder if my split system is activated and how to reset it.

If the reservoir(s) was completely empty along with low fluid in the MC bore, more than likely the MC and complete system has to be bled. Does the system have a PDV (pressure differential valve) on it? If so it may have to be reset.

The MC can be bled on the car if the MC is perfectly level, otherwise bench bleeding.

Are you able to post a photo of the install?

[miker98038]

I agree with K. There’s always a possibility that the fluid got low from pad/shoe wear, but I’d be looking real close for where all the fluid went. A small leak can become a large one suddenly, and that’s a really bad feeling. Been there. Used the t shirt to clean off the seat.

[40cpe]

The brake warning light switch on the distribution valve was leaking. I replaced it.

[KULTULZ]

Is there a warning lamp (dash) running off the switch? If so, is the lamp illuminated?

Where did you find the switch? Most of these conversions use GM parts.

[40cpe]

Sponsored Links (Register now to hide all advertisements)

There is no warning light installed. The switch appears to be a simple grounding device for the warning light bulb. I'm going to the shop in a little while to see if switch terminal is grounded.

I ordered the switch on line, it's a GM switch.

[KULTULZ]

OK, so it is a GM VALVE.

You can buy a special block-off for the switch if no lamp is desirable. It will trap the pintle inside of the valve from moving.

Interested?

[40cpe]

There is no continuity between the switch terminal and ground. Can I assume that the valve is distributing pressure to front and rear circuits?

[KULTULZ]

Can I assume that the valve is distributing pressure to front and rear circuits?

It has nothing to do with the switch (unless the switch fails as in your case). There is a pintle within the valve that will slide and trip the switch if there is either a front or rear circuit failure (pressure/volume loss). Without a functional switch, there is no need for the pintle as it will only restrict pressure in the circuit it slides into (also will cause difficult circuit bleeding).

In your situation, the PDV is only an expensive DISTRIBUTION BLOCK.

Is the PDV free-standing or is it within a COMBINATION VALVE?

The tool will prevent the pintle from sliding if a circuit failure. It will also prevent switch failure as has happened here. The PDV is mandated by FEDERAL REGULATION (1967) to alert the driver of a brake failure.

It (pintle) does not totally block off the failed braked circuit. That feature is designed within the MC (dual reservoir/piston) itself.

Pressure Differential Switch

The pressure differential valve is the device that alerts you if you have a leak in one of your brake circuits. The valve contains a specially shaped piston in the middle of a cylinder. Each side of the piston is exposed to the pressure in one of the two brake circuits. As long as the pressure in both circuits is the same, the piston will stay centered in its cylinder. But if one side develops a leak, the pressure will drop in that circuit, forcing the piston off-center. This closes a switch, which turns on a light in the instrument panel of the car. The wires for this switch are visible in the picture above.

SOURCE - https://auto.howstuffworks.com/auto-...ster-brake.htm

[40cpe]

Kultulz, My understanding is that the piston, or pintle, that slides within the distribution block blocks (at least partially) the side of the block that is experiencing low pressure. At that time the sliding pintle grounds the switch to illuminate the brake warning light. My thinking is that if the switch isn't grounded, the piston/pintle is centered and allowing flow to both circuits.

I just took the car out for some tests. When I apply the brakes for a casual stop, things seem normal. If I continue to press as in a panic stop or from highway speeds, I get a very hard pedal and no increased braking. If I continue a panic stop, the left rear wheel will slide a little just before the car completely stops. I came home and jacked up front and rear of the right side of the car. I started the car and blocked the brake pedal. I couldn't turn the front or rear wheel with my hands. The power brake chamber seems to work until the brake pedal gets hard, so I don't know if it is faulty or not.

[KULTULZ]

Originally Posted by 40cpe

There is no continuity between the switch terminal and ground. Can I assume that the valve is distributing pressure to front and rear circuits?

assume = a$$-u-me

Without the lamp, it may prove difficult to determine the pintle having moved. Possibly using a test lamp.

The procedure to center the pintle (once tripped) usually requires the use of the warning lamp.

The fitting (tool) I am describing does not allow the pintle to move.

If any of this is not clear, yell at me. I am not proud.

See if the attached shows large enough to cipher -

[40cpe]

Thanks, those illustrations are helpful. They verify that the brake warning switch does provide ground to the lamp.

[dmsfrr]

Originally Posted by 40cpe

My '55 Victoria has power disc/drum brakes installed by a previous owner ... When opening the reservoir, I noticed ... The reservoir was empty....

Is there a chance the car has one of these original style fender mounted brake boosters?
When the diaphragm fails engine vacuum can suck all the brake fluid out of the master cylinder.
It may be part of the problem you're having?
.

[KULTULZ]

They verify that the brake warning switch does provide ground to the lamp.

No don't worry about the switch. It is not being used in your setup.

What I am trying to say is there is a tool that can be used to eliminate the switch altogether and keep the pintle in a fixed position so this won't happen again. Most likely the switch is an off-shore piece of crap and needs to be eliminated (IMO).

The only way to determine if the pintle has moved without the WARNING LAMP feature and without pressure gauges is when bleeding either front and/or rear circuits if the fluid will not expel easily from either circuit (bleeders)

[40cpe]

Thanks Kultulz, I have pressure to both ends. I have bled the brakes.

[KULTULZ]

You are more than welcome ...