Help me spend my money

[andy198712]

sounds like a terrible car lol
reinforces its all about balancing the brakes though huh?
(army or Navy?)

[helowrench]

Yes,
brake balance is very important, and usually you find the problems at the worst possible time.

[Ol'fogasaurus]

...67' 1500 beetles were first to come stock with disks here....

. I used an early dual-circuit M/C with the discrete residual-pressure check valves and learned the hard way that they aren't compatible with discs (first set of pads was shot in ~10K miles).

If you know, what size of residual pressure valves were installed?

[Piledriver]

...67' 1500 beetles were first to come stock with disks here....

. I used an early dual-circuit M/C with the discrete residual-pressure check valves and learned the hard way that they aren't compatible with discs (first set of pads was shot in ~10K miles).

If you know, what size of residual pressure valves were installed?

It really doesn't matter, discs need to fully release pressure so as not to drag on the rotor.
(The square seal flexing actually pulls the pistons off the rotor a thou or so when released)
Residual pressure valves are an exclusively drum brake thing, never use on discs.

The later master cylinders eliminated the residual valves and just used small drillings, disc compatible.

[Ol'fogasaurus]

The rule of thumb is 2#s for disc and 10# for drum brakes. Now days disc residual valve is usually located in the distribution block usually found on the firewall that the MC feeds.

The reason for the valve is the potential bleed back of the brake fluid into the MC reservoir especially when the slave cylinders/caliper/turning brakes are mounted above the MC which, if it happens, can allow the shoes/calipers to back away from the drum/rotor which causes either a lot of pedal travel or pumping up of the brakes.

A lot of guys riding in the sand with discs think that they are OK with 10# on the rear (only as they don't have front brakes) brakes.

Lee

[Steve Arndt]

I have a 2 pound RPV on my rear discs on my street car. Works perfect, no dragging.

[Marc]

I dunno what the pressure rating of those OEM RPVs was...it was an early `68 M/C IIRC and had three of them, all apparently identical (one for each front line and one for the rears). I didn't recognize them as RPVs and assumed that they were just thread adapters - that style of M/C won't accept regular bubble-flare lines without them. The pressure must not have been too high, though, since I didn't notice any drag - but the pads sure did go away fast. When I realized the problem, I took the two front ones out, clamped them in a vise, and used a drift punch to knock the guts out of them which left a hole about ⅛" in diameter (NO restriction-drilling effect) and the brakes functioned fine thereafter.
Another thing which RPVs do (and restriction drillings do not) by keeping a light pressure on the wheel cylinders is to help the seals work better. Slight fluid leakage is fairly benign, what's more important is to prevent air from being drawn into the system on the pedal upstroke. More modern wheel cylinders incorporate a cup seal expander (a plastic disk inside the seal with a light spring applying pressure to physically push the lips out.

Both the original `67 (two stoplight switches, no warning lamp), and the early `68 with a third mechanical switch for the warning light, master cylinders have been obsolete for decades; the 113 611 015BD "universal replacement" is the only part available anymore - it incorporates the restriction drillings in all three outlet ports to slow down the fluid return flow (and the chances of sucking in air past the seals) but they don't have any effect on the line pressure at steady-state.

[Ol'fogasaurus]

Steve, how old are your soft lines or what condition are they in. The soft lines are another place where pressure to the calipers can be stymied.

[Piledriver]

I have a 2 pound RPV on my rear discs on my street car. Works perfect, no dragging.

If you are running discs, why? Suckback through calipers is not a concern.

[Steve Arndt]

The calipers are higher than the master cylinder (like Lee mentioned).

The front circuit has one built in to the master cylinder as I understand it on the dual circuit unit units.

[Marc]

There are no residual pressure valves in the 113 611 015BD (or any other current-production ACVW M/C that I'm aware of). Once upon a time it was common in some Detroit iron, but nowadays the feature (if present) is built into the proportioning valve that's omnipresent on modern cars.