I have been looking at Speedway's catalog on brake systems and in the "tech tip" diagram it shows a residual valve on the lines to the front and to the back. A 10 p.s.i. valve for drum brakes and 2 p.s.i. for disc brakes. I have read that some master cylinders have them built in. How would I know if the one I bought(new 1967 Mustang for drum/drum) has them? Also I mounted the master cylinder under the seat well below the wheel cylinders.
yep you need them with the master down there. I think the pressure valve on single circiut mustang masters is in the outlet fitting-unscrew it and have a look-if its dual circuit will be integral in the piston.dont trust me on this,havent had one apart for a while,but you were gonna pul it apart to check it out anyway ..right?
This is what I have learned so far about these residual valves(RV), If you do a drum disc swap if is recommended to install one inline. These can be used in conjuction with proportioning Valves in fact should be (so I hear). Basically what they do is keep the line pressure set at whatever they are set at. for example if you have a 10LB. RV going to your rear drums, there will alway be 10lbs of pressure going to the rear brakeline after the valve. Also there are two type a 2lb and 10lb because 10lb is what you supposed to use with a drum setup and 2lb is what you'd use with a disc setup. I also believe you can use two separate RV's for front and rear useage. I personally am going to use a 2lb to the rear disc, I am going with on my old ford. The reason you don't want to use an adjustable one is that many thing can happen and you'll have too many variable to figure out what is wrong with you brake setup. ON the adjustable the tightening cam come loose or just not ever be "adjusted" properly by you. Thats why those preset ones fit the bill. good luck- everyone else you can call it on me if I don't ake sense!
When swapping discs onto the front of a car originally equipped with drums, use a 2lb residual valve to the fronts and a 10lb one to the rear (assuming you still run drums out back). This has nothing to do with where the master cylinder is positioned on the vehicle, you should run them as indicated to insure proper brake function and pedal feel without excessive travel.
Residual valves are necessary in ANY drum brake application and are built right into the master cylinder (for domestic applications). These are on the order of 10 psi and are necessary to prevent the fluid from being sucked back into the master cylinder faster than the return springs can pull the brake shoes back to the anchor pins. If the fluid were allowed to surge back as the pedal retracts, it would pull air into the wheel cylinders as a result of the vacuum the retracting master cylinder piston creates in the system. The residual valve is there so that the brake shoe return springs force the fluid back into the master cylinder, thereby preventing air from being sucked into the system. It's when you get into disc brake master cylinders when you run into problems. Disc brakes won't work with a 10 psi residual valve. They'll stay partially applied and, eventually, seize up. Most factory firewall-mounted master cylinders WON'T have a residual valve in the brake line. If, however, you MOVE the master cylinder worn under the floor, you run into a situation where the brake fluid from the calipers drains back into the master cylinder because the master cylinder is at or below the height of the calipers. When this happens you have to pump the brakes once or twice to get a pedal when the havent been used in a while. This isnt such a good thing when youre on the interstate and have to use the brakes after a long period of operating on cruise control. A panic stop will leave you with a stain on your seat if youre not quick enough. In this situation youll need to install a 2 psi residual valve/ 2 psi isnt enough to cause the calipers to drag but its enough to prevent the fluid from draining back into the master cylinder. All single reservoir master cylinders will have a 10 psi residual valve in them as they were designed for drum brake applications Dual master cylinders hit the streets when the need for dual pressure (disc and drum brakes require different line pressures) became necessary. If discs were an option, you could see one of two types of master cylinder on the car. Drum/drum or disc/drum. An example of this is the 72 Dart I own as compared to the 76 Duster I also own. Both have dual master cylinders but the Dart is a drum brake car while the Duster is a disc/drum car. From all outward appearances the master cylinders look identical but theyre NOT. In fact, Midas put a new master cylinder on my Dart when my daughter was driving it ad they put on a disc brake master cylinder. I caught it right away ad made em put teh old one back on. (She broke a brake line on the front and they said she needed a new master cylinder). Standard practice they said. The master they took off had less than 2,000 miles on it. So much for the experts Anyway . Drum/drum master cylinders will have a residual valve in each port. Disc/drum master cylinders will only have one residual valve in the drum brake port. Disc/disc master cylinders wont have residual valves in them.
I've never tried this, so here's my wild guess, can you hook up a pressure gauge and line to the M/C, build up some pressure and see if 10 lbs shows on the gauge?
This is some good info, often overlooked I would assume. Thanks for the lesson,Larry Oh yeah, I'm serious, not patronizin. Thanx
desoto- So what you are saying is that the master cylinder I bought will allready have the valves installed? I guess I can put the system together without the after market valves and see if it holds the pressure/ Thanks Fred
i don't think the `67 mustang has the residual valves built in, i think they were in the combination valve. i have used this m/c many times and i always put residual valves inline.i'm not 100% sure of this,but i took one apart onetime and couldn't see it,but it doesn't hurt if you add them inline in the brake system.they are not REAllY a lot of money,i'd ad them to be sure.
Fred, I've got a Mustang master in my T below the seat. I put the 10lb residual in back, a 2lb in front, didn't pull anything out of the master, and everthing works fine. 1659 miles and counting! Rick
lakes how ya doin? hey I had a similar problem / question and what I learned was that it doesnot hurt to have more than one residual pressure valve.. in other words even if your master has a valve built in it will not hurt to install another in the line to the rear. therefore when in question install one later sawzall ps is this for the car I saw at pee all uppp?
Hi, a '67 dual master doesn't have them built in.I took my new one apart to check.I have a 40 Ford and drums front and rear .I have the Wilwood red(10lbs) valves in there.They work. Michael
poke a small rod (welding rod or coat hanger) in the hole. If it hits a piece of rubbger, that's the residual valve. Gently screw a sheet metal screw into the brass cone and pull the cone out to remove the residual valve if you want to use the master cylinder on a disc brake line. ....and, yes, more than one 10 psi residual valve won't hurt anything. Just don't use a 10 psi valve in a disc brake line.
can anybody tell me where they have to by mounted for my drum/drum application. Can they go vertical or horizontal close to the master cylinder or close to where they split to go to the wheel cylinders?
i have the aforementioned setup, and am having issue with excessive pedal travel and a spongy feel, like its never really getting the job done. would a disc drum master with larger bore help? and why not use wilwoods? Thanks, D i have
Fat Hack? Unkl Ian? Anybody that has pics of their setup, good experience with a certain setup? I am looking at using the wilwood 1 1/8 remote fill, just hog out my stock one and mount it on the end, I saw it done somewhere but can't remember
Does a 40 ford master have this valve built in? I'd assume so since it was built for under-floor operation. I'm running without one..
I got a 35 ford roadster. im using 40 Lincoln drum brakes front and rear. I have installed a dual master out of some jap an import (Aisin pn. 47201-12761) no residual valves in it with a little (stress Little) it bolts up in the stock location . I have installed the wilwood residual valves Blue 2 lb. in both the front and rear lines at the master cylinder. I also run a proportioning valve (obviously in the rear line). I have about 9 thousand miles on this set up and it stops on a dime everytime. Its been tested a couple of times ............
Don't confuse a residual valve with an adjustable pressure valve. Typically the adjustable in line valve is used to reduce pressure to the rear so they don't lock before the fronts. This valve does not serve as a check valve. The debate of master cylinder above th floor Vs below the floor has to do with drain back. If your master is below the caliper (Disc only) there is a chance the fluid will drain back into the master and pull in air. A RPV will prevent this. If the master is on the firewall it will can not drain back into the master. Usually only an issue for disc brakes, as there is not enough fluid in a wheel cylinder, compared to a caliper.
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