Zr1bandit

Getting ready to,bleed brakes on my 1970 442 W-30 and was wondering if I need to use a brake proportioning valve tool when I bleed the brakes using a vacuum pump ?.

matt69olds

I have never used one, and never had any issues bleeding brakes. To be honest, I’m not exactly sure what it’s supposed to do. I assume it’s to hold the internal valve in position to allow maximum fluid flow?

70W-32

The 1970 cars use a distribution block, not a proportioning valve. a tool is not needed.

joe_padavano

The tool is used on the metering valve part of the system, not the proportioning valve. The 1967-70 cars DO have a metering valve, it's the valve below the master cylinder. The CSM does say to use the tool on these cars, however like Matt, I've never used one in half a century of working on these cars.

This is the typical 1967-1970 metering valve. Note the rubber boot over the pin that you are supposed to depress.




And for completeness, this is the 1971-up combo valve. Again, note the metering valve section at the front that has the pin that is supposed to be depressed.

Zr1bandit

The tool I’m referring to goes into where the switch terminal is on the distribution block.

joe_padavano

Well, that's completely unrelated to the prop/metering valve discussion. I have one of those tools and haven't used it yet. If you are pressure bleeding the system either manually with the pedal or with a pressure bleeder on the M/C, the tool will prevent the differential pressure switch piston from being forced all the way to one side, which usually results in a panicked post here. I use a vacuum bleeder and haven't had a problem not using the tool.

Zr1bandit

Thanks. That’s the tool,I am referring to. Thanks. My brake pedal is very stiff and I am thinking I may have a bad back flow valve my power booster. It’s the only part that I used from the original car when i restored the car.

joe_padavano

If you are talking about the plastic vacuum check valve in the hose from the intake manifold, yes that can certainly cause a loss of booster assist if it is bad. New valves are available from Dorman and take about 30 seconds to install.

Zr1bandit

Yes. Thinking bad check valve. Got new one coming Thanks

zl1 camaro

Remove the valve in the vacuum hose and hook it up direct, if the brake pedal improves that's the problem, or just remove the hose from the booster, start the engine and see if there is any vacuum there, if no vacuum valve is bad.