I have been getting mixed replies from people I spoke with - what can you guys tell me? Some are telling me yes. Some are telling me only if the dual master is located mounted on frame do you need residual valve. I the answer you guys say in yes in Firewall mount application -- what lb residual and does it go to; front or rear brake
From your other post it seems you have a firewall mounted master cylinder and 4 wheel drum brakes. Most drum brake master cylinders are already equipped with residuals so if you are using a drum brake master you are most likely fine. If you have a drum brake master with residuals built in you don't need additional ones in the line.
No!!! Not needed. More important is having master cylinder and wheel cylinder diameters properly matched. Then you shouldn't need a proportioning valve either. Phil
Fordstandard....just go drive the car in stop and go traffic for a while. I'd bet your friend already fixed the problem. Asking all these questions about something you don't really understand is gonna confuse the **** outta you. Just go drive the car!!! LoL
UPDATE - I have corvette style 1" bore dual master with no built in residual , I do have the original 53 Chevy drum brakes up front , and a Chevelle Rear.
Is your pedal really low and you have to pump it to get a firm pedal? If not...you most likely don't need any additional residuals. Residual valves just keep the fluid SLIGHTLY pressurized. (For lack of a better description!) They won't keep brake shoes tight against the drum. The shoe return springs are too strong. My T had issues that required residuals and the issue was basicly NO brakes unless you double pump at every stop. There was no problem with brakes dragging I can tell you that!
No Phil, you are SO wrong on this. You shouldn't be answering questions you obviously don't know enough about. Sorry, hate to be rude and call someone out on this but I hate when someone post answers that are wrong, especially when it comes to safety issues. To the OP. Yes, you need residual valve with drum brakes no matter where the master is mounted. If your not using a drum brake master that has them built in you will need inline valves. You said your using a Corvette duel master so you will need to add them inline. Drum brakes use 10 lb. valves. FWIW master and wheel cylinders bore size doesn't have that much to do with proportioning valves either. Front to rear weight bias, tire sizes (big & littles) ect does.
I agree, whether above or below the floor, drum brakes require a residual valve. The shoes need to be held out or the brakes get very spongy. Rebuilt or new masters generally come with the little rubber cones in the outlets which precludes the need to buy and plumb in two external residual valves. Warren
Residual valves are used on almost all factory drum brakes. The 10 psi or so does not over ride the spring pressure on the shoes and keeps the wheel cylinder cups pistons and push links tightly together. It is not enough pressure to move the shoes.
As Hackerbilt stated, the residual does not/cannot hold the shoes out. The main purpose of drum residuals is to keep air from entering past the wheel cylinder cups during brake release, period. A side benefit is a slightly tighter pedal, even on post mid-'70s drum systems when residuals became obsolete because of cup expanders and better cup designs, along with standard front disc brakes.
The adjusting wheel and ***ociated cable and levers keep the shoes in the correct location in relation to the drums, not the residual valves. Drive the car and see how the brakes act. You will need to drive a couple blocks then stop, drive a couple blocks and stop. If you are pumping the pedal to get it to stop, go home and check the adjustment. Go for a drive again, if the same thing happens, you need the valves.
Was not thinking clearly. I should have said IF you use a master for drum/drum, it should have residual valves built into the outlets. Phil
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