The Stovebolt Site Forums The Shop Area General Truck Talk '59 Chevy Dual master Cylinder up-grade

I am begining the replacement of the entire brake system on a 1959 Apache 3200.
I will be replacing the master to a dual resivour for a 1970's chevy 1/2 ton truck.I will be using the stock 4-wheel drum brakes as were stock on this truck.I read the tech tip for this application, but I have a few additional questions. Is a metering/proportioning valve required for this application? And do I need to install residual valves as well.

As I understand it the metering valve controls the ammount of pressure applied to the front wheels (which is greater) and the rear wheels (whis is less). Or is this accomplished through the bore in the mastercylinder.

And the residual valve is supposed to keep positive pressure on the wheel cylinders to prevent air from being sucked through the wheel cylinders.

Any help you can provide would be greatly appreciated.

Hy Village_Idiot, if you purchase a master cylinder that is designed for a drum/drum application it will have residual pressure valves built into it, so no others should be required. As to the metering/proportioning valve, I'm not sure if one designed for a drum drum system exists. Because a pickup is usually so light in the rear end, rear wheel lockup can be experienced. My advice would be to install the system, and if you feel you're experiencing too much rear wheel lockup, I would install an adjustable proportioning valve in the rear brake line. Of course if you can find a metering/proportioning valve for a drum/drum system then I would install it. The supplier you purchase your brake system components from "should" have some technical expertise, so take advantage of it and ask for their opinions on your installation, hope that helps.

3B
thanks for your reply. I appreciate your time. I bought the master cylinder locally at a chain parts store, unfortunately not much help there.

Make sure the 70s truck master you bought is for drum,drum application,the one I used on mine is for a 67 1/2 ton chevy.I went to the NAPA web sight and checked until I found the right one if its for disc drum it will not work right.No metering valve is needed.

Pete

I made sure the master was for a 70-72 1/2 ton drum drum no power(dunno if that matters)i didnt know the residual valves were built in, but i guess even the village idiot can score once in a while

You need residual valves if the master cylinder is mounted under the floor, which probably makes it lower than the wheel cylinders: you need 2 of them, one for the front, one for the rear.
If you mount your master cylinder on the firewall, not needed.

Oh good catch... do i need 2lb or 10lb for a drum/drum system?
Thanks for your time

Hy guys, a master cylinder designed for drum brakes already has residual pressure valves in it, just like the stock single system master cylinder that functioned in the truck for years, hope that helps.

3B,

Do I understand you correctly that even with the master cylinder mounted in the stock (under the cab)location residual valves will NOT be necessary since the are built into the maaster itself since the master IS designed for a Drum-Drum system.

Hy Village_Idiot, yes you understand me correctly, if the master cylinder is designed for drum brakes all around then it already has residual pressure valves built into it. It seems to me that the brake system suppliers have contributed to the confusion over this issue, they market a master cylinder originally for a Corvette, which had disc brakes all around. That master cylinder would require residual pressure valves if used in a drum brake application. Also if a disc brake master cylinder is mounted below the level of the calipers or wheel cylinders then a 2 p.s.i. residual pressure valve is required for the disc brake circuit, in addition to the 10 p.s.i. residual pressure valve required for the drum brake circuit, regardless of the master cylinder mounting position, I hope this clarifies the need for residual pressure valves.

3B,

Again Thank you for your time.

Just a question. Village Idiot, did you say you got a 71-72 master? The 71-72 1/2 tons were all disc/drum; power or manual.
The 67-70 1/2 ton models were drum/drum.

I got a master cylinder for a '70 1/2 ton and made sure the counter person clicked the option for drum-drum

Cool. Just checking. Hate for you to get it all together and then find you have the wrong master.

Happy wrenching,
Gary

I appreciate you taking the time to give your input. I will take all the help I can get.