residual valves?

[Panelfantastic]

Tried to search, no luck. Putting together 4whl disc for my panel.
What's the story with residual valves? How do you know when you need them? My understanding was, on lowered vehicles where the M/C could possibly be lower than the caliper, they are a necessity to prevent flow back into the M/C. but I've also read they cause "dragging" in some cases...
I'm also trying to learn about the porportioning valve but that seems a matter of personal choice/control than an absolute need (given the tire/wheel sizes are similar, from the posts I've read)
What are your experiences?

[kdanie]

If you use a 2 psi residual pressure valve it should not cause the pads to drag. I think if your MC resivour is well above the calipers, like in the trunk the head pressure should make it work ok with out the residual pressur valves. Some MCs have built in residual pressure valves, if you are using a drum brake MC it may be built in. Drum brakes use 10 psi residual pressure which is too much for disk systems.
hope this helps some
ken

[Panelfantastic]

Thanks Ken, on researching a little further I discovered that the residual valve is needed in all applications if you want to keep the pads or shoes tight against the disc/drum for a solid pedal feel. As you pointed out, the 10lbers are for drums (more effort needed on drums) and the 2lbers are for discs.
I've still gotta research which M/C will be best for me to use on my 4 whl disc conversion. Thinkin' maybe a 944 unit, seems to be what several others are using.

[chigger]

Wilwood has excellent articles on both residual valves and proportion valves. When to use them and why. www.wilwood.com
www.stockcarproducts.com also has some great tech articles.

The 944 or stock dual MC question comes up alot. It is probably about 50 50 divided on what you use. Both camps seem to like the outcome either way. Read the articles and decide what you want, other wise you won't be happy.