1948F-1Pickup,
Do you really believe a 10-15 lb (approx. normal OE production range) residual valve can overcome shoe return springs of 50-100 lbs or more?
The "
keeps the shoes in close proximity to drums" makes no sense at all, (although
is/was shared by some misinformed brake suppliers) as the normal shoe to drum
total clearance is .025"-.030". That's .0125"-.015" per shoe. The shoes in a drum brake
should always return solid to their anchors,
by design.
My 35 year dynamic brake testing experience started in '71 at Bendix, when residual valves began a phase out because of cup expanders, better cup designs, and front disc brakes that do not need residuals.
Bluebell,
I do agree with your first sentence, and is why I install/recommend residuals on
all drum brake systems. :-)
It is the very strong shoe return springs that
can and
will allow air to enter past the cylinder cups during fast release, fact-not opinion.
Production residual valves ranged from around 10 lbs to about 18 lbs from the info I've been able to gather. The after market in line valves are all rated 10 lbs for drums, and 2 lb for discs.
Production disc brakes never needed or used residuals, as master cylinder location was high on the firewall before modern discs were available. The aftermarket 2 lb valve should
only be used when the calipers are higher than the master.
Early single system residual (check) valves were usually located at the end of the bore, but most dual masters have the valves located behind the tube seat(s).