Residual pressure valves question

[Tom Wells]

I've read that 2lb residual pressure valves are needed if the master cylinder reservoir is level with or below the calipers. Mine are OK in that regard.

QUESTION: Are the residual pressure valves needed if the brake lines themselves are located about a foot above both the master cylinder and the calipers?

My brake pedal isn't as high or firm initially as I'd like. Two quick presses firms it up some.

Tom

[Jack21]

Tom,

If you look at the brake component location on some '30's and '40's era cars, the master cylinder was located by the floorboard, and below the height of the wheel cylinders. Brake fluid could siphon back into the master cylinder under those conditions. The residual pressure valve functioned as an anti-drainback valve. If your master cylinder is located above the height of the wheel cylinders, you shouldn't need residual pressure valves. Something else is causing your wheel cylinders to retract. Look at your parking brake adjustment.

[427sharpe]

I presume you are running discs @ all 4 corners?? If your lines run that far above the master, you have to make SURE that all the air is out! Air will gravitate to the highest point in the system and stay there. Are you 100% SURE that ALL the air is out of the system? If you are, the lack of residual pressure valves could very well be causing your weak pedal. Modern calipers have a square cut retaining seal that acts as a nominal retractor to pull the caliper piston back from the rotor. If there is no resistance, it may be drawing them back too far. A quick check: raise one end of the car just enough to get the wheel off, and then lower the car to its approximate ride height. If you can get to the brake pad, see if it 'wiggles' freely. If it does, ck again after one pump of the pedal..is it tighter? If so, you need a residual pressure valve to keep them from retracting so far. If you are using Tilton masters, they offer a variety of residual valves to help you tune the brakes. You want just enough pressure to keep the pad in LIGHT contact with the rotor, but NO DRAGGING. I think I ended up with 1.5 psi valves in my car, and my pedal woes went away.

[Tom Wells]

Hi 427sharpe,

Yep discs at all four corners:

Front are PBR (SVO Mustang or Corvette etc)
Rear are Jag inboard, widened for vented discs

Master cylinder is Subaru power.

I think I'll try to make sure that no air is in the lines, then maybe try the 2psi valves from Wilwood.

Regards,

Tom

[Roscoe]

Tom,
I have a set of Wilwood valves that I never used. Brand new in the bag. You can have them for 10 each plus 4.00 shipping.
Let me know
roscoe@priveye.com
Roscoe