did a search and didn't find a diagram for a 2 line brake system. got an "a" coupe. with disc fronts and drum rears. looking at the speedway catalogue diagram it shows the front line going from the front reservior thru a 2 psi block to a tee and then to the front calipers. the rear shows a seperate line going from the rear reservior thru as 10 psi block then a proportioning valve and to a tee then to each drum. is this correct? what does the adjusting valve do? thanks rer_239
The valve is to adjust the break pressure so you do not have your rear breaks lock up first.You can take away some of the pressure,so the front locks up first.
The 2psi/10 psi check valves are not needed if your master cylinder is higher than your brakes ie firewall mounted. They are important if your master cylinder is low- such as frame mounted. Jim
Jetnow1 Being that he is talking about the brakes that will either save or destroy his life, are you sure about this response?
Here is something IMPORTANT to consider on that Speedway diagram, it is correct if your master cylinder is mounted on the firewall, but it is incorrect if your cylinder assembly is mounted under the floor. In this configuration, you need to reverse the lines into the master, so the line closest to the mounting point/bracket or the brake booster will go to the front brakes. Always consider having the brake lines going to the front brakes coming out of the master cylinder where the pushrod enters the cylinder first. Or the larger reservoir gets the front brakes, either way you wanna remember it. Hope that helps.
this is half true. The 2psi isn't needed if the master is on the firewall, but the 10 psi still is. The 10 psi is to overcome the return spring tension inside the drums. Without it, you'd have to "double stab" to get good solid pedal EVERY time you hit the brakes, because the shoes would have fully retracted away from the drum.
Lots of good info here. i have a little different issue. My car has front and rear disc, and power brake set-up mounted to the frame. There is residual valves and a adj. potioning valve plumbed like the diagram above. I have about 1" of pedal at the most. The brakes seem to work great but with the car on stands I seem to get more caliper drag than I am use to. I can turn all the wheels, but there is diffenitly resistance. Any ideas I should look for before I take the car on it's maiden voyage?
One thing not mentioned is placement of the T for a brake lite pressure switch (if you are using one). I really dont know if it matters because Im not sure how much pressure it takes to operate the switch, but I always place mine in the line to the front calipers (there wont/shouldnt be a factory check valve in this port of the master cylinder), before the inline check valve, where there is the least chance of having any pressure against the switch to avoid having the brake lites on when not braking.
unbolt the master from the booster to check and see if the pedal free travel is wrong, holding pressure against the master cyl. you have the blue 2 psi residuals, right?
My residuals are stainless or aluminum. I can't find any markings on them either. How much free pedal should I have? Is the rod between the booster/ master adjustable? Like I siadf the wheels all spin, but it seems like there is drag and the pedal takes very little movement to activate the brakes.
I'm often curious about the residual valves with under-floor mounted master cylinders: My '54 Buick came from the factory with an under-floor master cylinder, and it doesn't have residual valves. Yet we're told we must have them to keep the brake fluid from draining back into the master cylinder? If no air can get into the system at the wheel cylinders, it's not going to drain back. Gravity will not overcome a vacuum with brake fluid. -Brad
IMO it's not about drain back, like the fuid running downhill back to the master cylinder, it's about residual pressure, and holding the brake lining the proper distance from the friction surface. Your '54 Buick has a residual valve in the master cylinder, rather than an external one like the aftermarket offers. it's a little "hat shaped" disc with holes in it and a rubber diaphragm. It can be taken out, or left out during a rebuild, leaving you with no residual pressure.
Do the valve pressures stay the same if you run drums on all four corners? Everything I see shows disc fronts.
The only point of residual valves is to keep the cups in the wheel cylinder expanded so they seal tightly, they are virtually obsolete now as most springs in wheel cylinders have a cup expander built in. Put pressure gauges on a brake system some time, 10psi is negligible and is not to overcome the spring tension, that's what metering valves are for....lots of misinformation on brake systems. Sent from my iPhone using The H.A.M.B. mobile app
The Jalopy Journal
