Got to talking to some of the guys a while back. Mainly pertaining to the - reported - many failures of Willwood 2# residual valves. They're recommended for installations where the front disc brake caliper cylinders are higher than the - most times - frame mounted Master Cylinder (M/C). The residual valves are designed to hold a minimal amount of pressure - 2# - in the front lines to prevent fluid from traveling back to the M/C and perhaps allowing air into the front brake lines. If you have a firewall mounted M/C and no leaks, you have no problems. Along those lines, how about a firewall mounted M/C reservoir? This would simulate the higher up M/C and fluid would be unable to move toward the M/C from the caliper cylinder due to the gravity impressed head of fluid above it. M/C's are constructed in such a way as to forestall fluid leaking from the cap to M/C body interface. This would allow fittings to be installed in the M/C cap that would connect to lines leading up to the remote reservoir on the firewall. Building a reservoir shouldn't be too difficult. Exhaust tubing, some welding, a little paint would do it. Even better - for an aluminum afficionado such as myself - a short piece of thick wall aluminum tubing, bottom cap TIG'd or JB Welded on, some threads cut in the top, a removable O-ring threaded cap for the top, a touch of bracketry to make a good looking firewall install and you'd be in business. Using an even thicker wall piece of aluminum tubing would allow machining in of fins similar to the popular Beehive oil filter. A couple of lines to finish it off and you'd be done. Braided stainless would be my choice, but you could run hard lines down to the M/C area and have a short length of flexible line if desired. Since fluid levels would be checked at the reservoir, the M/C cap wouldn't have to be removed. Along those same lines, Speedway makes a nice fluid level indicator - for rear ends, but it would work here and you wouldn't have to remove the cap very often. http://www.speedwaymotors.com/xq/aspx/paging.yes/dept_id.325/display_id.3807/qx/Product.htm These are dependable little gadgets, commonly used in industry and look cool in the hot rod environment. Perhaps the remote fluid reservoir is the answer to a question nobody asked, but it strikes me that gravity is a whole helluva lot more dependable than a prone to fail mechanical device. I realize as well that these remote reservoirs are on the market - in billet form - but they seem to be more for the trinket value than for the convenience or ease of fill factor. It ain't billet if you make it yourself....
Doesn't bending the brake lines into a series of loops near the M/C help keep air out of the lines as well? (I am not suggesting this as a replacement for a residual valve.)
I think the coiled brake line is a vibration damping device to help keep the brake line from breaking off near the fitting. Usually seen on the longer runs of hard line. Getting back to the remote reservoir bit, a single down line from the reservoir could be used and have a "T" set up for each reservoir at the M/C so as to supply both ends of the M/C with make-up fluid.
Nahhh, that would make sense and be too easy.... I've been hanging out in the garage knocking out aluminum brackets and other things. I want to get the little stuff done before I get into the drive train build. Otherwise, I'll fire the car, deem it good for now, start driving it and maybe never finish some of the ideas I have for it. Two trunk brackets and three lock pin bases to date on the trunk latch install . . . and I'm still contemplating changes.
No. They don't have a siphon problem from what I understand. The residual pressure is there to keep the cups expanded so they don't leak. If there is no pressure the cups relax far enough to allow air into the system when the brake pedal is allowed to return to rest. Yeah, been keeping busy. Our new dachshund pup drags me out at the crack of dawn....
When I built my truck brake system, about 16 years ago, I did not know about residual valves. I bought the valves about 3 years ago but they are still on my desk in the office of my shop. My brakes work fine with out them but they are not as firm as when I first started driving the truck many years ago. Someday when I redo the old truck I will instal the residual valves to see how much difference it makes. I am not saying you do not need them, but it my case the system seems to work fine without them.
Me too! Personally I think it's a myth perpretrated to sell parts. MHO I know guys have problems but I personally don't think it's a result of syphoning or the M/cyl would over flow on the floor.
residual valves keep the pistons and pads close to the disc, without them the elastic action of the piston seals pulls the pistons back into the calipers which causes long pedal travel Larry
# Some new cars have "pull backs" in the calipers that intentionally pull the pads away from the rotors to eliminate that mileage robbing bit of drag. Do they have a much larger capacity M/C to counteract the same effect? I doubt the elastic "memory" of what usually amounts to an O ring on a piston is going to physically pull a piston very far, and the dust boot some of them have is usually a pain to feed back in, not get out of the caliper. # If the amount of "suction" of siphoning is actually powerful enough to "suck" a piston back in the caliper cylinder, then could I remove the flex line from the hard line and hanging it lower than the caliper and go eat lunch and after a period of time find all the fluid run out of the caliper and the pistons sucked completely back into the caliper bores, eliminating the need to use a caliper piston compressor tool when changing pads? If the caliper pistons don't move, freely, and their seals don't leak air back into the system, the fluid isn't going to siphon anywhere. From my experience, you have to apply substantial pressure, more than 2 pounds, to a caliper piston to get it to move in a bore even with no fluid line hooked up at all. Siphoning "power" uses a function of height. I know this because when I siphon lawn mower gas out of my truck it comes out of the siphon hose fast because the truck's tank is a couple feet off the ground, but when I try to siphon gas out of my MGB it just trickles because the tank's only 7" off the ground. If siphoning is the problem on a low M/C system, I would think that over night the pistons would suck completely back in their bores and when the cover was removed from the M/C it would be overflowed up into the dust boot bellows. Anyone with this experience? I think if it does occur, it's only on some certain design calipers that agressively pull themselves back when at rest. (My M/C is sorta level with the calipers but I park with the back end down hill usually, no 2# RPV, and no proportioning/combination valve, and I haven't had a problem with this in 13 years)
yeah, I'd sure love to hear a story about someone having a problem, and then putting in an rpv and the problem is solved. On a sort of unrelated note, I decided it was time to fix the front brakes on the old truck, I seem to recall having worked on them in 1990, and the wheel cylinders were pretty well stuck and slightly rusted and leaking and not working well. The truck had been driven a few thousand miles a year. I guess you need to maintain these things more often?
biggest problem with making a remote is the venting of it and not letting out side air come in contact with the brake fluid.
the magical "pull back" is the square oring, and it will pull the pads too far away from the rotor if a residual valve is not used, whether its built into the m/c or inline all disc brakes need them, whether you doudt it or not Larry
Backwards: The new M/C's DO have a take-up facility to allow for the retraction of the pistons, but my organic processor is on the fritz (brain fart, CRS) as to the name of the M/C. C9 - what you propose WILL do what you are thinking: put a gravity "head" on the fluid to reduce the (supposed) necessity of a residual valve. It wasn't clear, and I'm sure you know, but the cap supplied with the master will NOT work with a remote reservoir. I tried with fittings tapped into the body of the M/C, but it leaked. You need a solid, well-fitting (and gasketed) cover, which is what I think you are proposing, and it'll work a treat. For the remote's cover gasket, try a motorcycle M/C gasket. It has a bellows to allow the use of fluid while keeping out the air. Without this, you run the possibility of having a vacuum in the system, which could pull fluid out of the system. Cosmo
In regards to the defective Wilwood residual pressure valves.... 4 to 5 years ago it seemed like 30% of the ones we installed were faulty but in the past few years we've had no problems with them. (knock on wood) We install them on every underfloor master cylinder chassis we build.
The Bendix rep. that conducted the seminar for the shops that buy their products, explained that the grooves in the new calipers are milled differently than the older ones we are familliar with. The walls in the seal groove of the caliper are not parallel. The wall of the groove closest to the pads actually slants out towards the pads. That lets the seal lean when the brakes are applied. When you let up on the pedal the seal springs back pulling the piston with it. In the old calipers with parallel walls, the seal could not lean so the piston moved inside the seal. When the pedal is let up the seal stays put. As the pads wear the piston will move inside the seal but it will always have the spring back space to reduce drag and improve gas milage which is the reason for the change. Bendix conducted the seminar to alert the shops that the new style calipers require a different "quick take up" master cyl. with a stepped bore. The problem occurs in the daily drivers too if the parts get mis-matched. I never memorized what year the change took place. I just made sure to order the right year parts. That's how the Bendix rep explained it.
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