First time to plumb brakes for an underfloor master and I have a few questions. Setup: Front: F100 11" Drums Rear: 1964 Ford Station Wagon Drums Master: Underfloor 1970's Ford Dual Bowl Manual Questions: 1. I believe I need to plumb in a front and rear 10 psi residual pressure valve? 2. What are the rules for the location of the residual, should it be closer to the tees or the master? 3. Do I need to use a proportioning valve? If so does it go before or after the residual?
Or use a late 60s dual drum type master cylinder, with built in residual pressure valves?or an older single drum mc with a built in residual pressure valve? Should not need a proportioning valve...although you might...those are kind of big rear brakes, for a car that's not a wagon. But I'm ***uming it's not a wagon, you didn't say what kind of car (or truck?) it is.
Great question, I hope you get some more detailed answers rather than suggestions for alternate master cylinders and other such drivel. I'm setting up an almost identical 4 wheel drum setup. I prefer a master cylinder without residual pressure valves myself. I have been told that yes an adjustable proportioning valve is needed so that you can adjust the braking balance between front and rear. Also front and rear residual pressure valves, (10 lbs.) The location of the components will be the next info to have.
Residual valves should be close to the master cylinder. I usually plumb the system without a proportioning valve and only install it if it is needed, it goes after the residual valves. 10 lb for drum 2 lb for disc.
If your master cylinder has a residual valve inside each port, you will not need the inline versions. I was told that you could check by sticking a small nail in port. If there is resistance, you have those little rubber "duck" valves already in the m/c ports. You probably do not need a combination valve for drum/drum, unless there is a big difference in front/rear tire size. If one were installed, it should be the closest to m/c. I have successfully mounted these below m/c on frame in attempt to clean up the looks of firewall mounted m/cs. Inline residual valves should be downstream, as stated, but closer the better to m/c. Some of the adjustable inline proportioning valves seem to just lower line pressure as knob is screwed in.
Drivel was probably the wrong word He has a MC, as do I, probably one that he bought as I did based on the recommendation of a shop like Boling Brothers. So, changing master cylinders would actually amount to spending more money. Isn't spending more money what we do playing with these toys anyway ?
If you feel the info you received was correct for your MC , then I'd go to the same source for info on the rest of your system...pretty simple.... dave Inotherwords , if the recomendation for the MC was based on your components , and not a WAG , they should be able to advise you further...
That's true and I will probably do so once I order up the front brakes. I was just curious to see what info the OP would manage to get here.
maybe, maybe not. The extra fittings for the valves would add up.... We each have different priorities. I like doing a lot without spending much.
As mentioned already, One of the problems with brake balance is the difference in tire sizes front to back. If you took a complete braking system off a normal car and installed it on your rod. If the rear tire dia. is much bigger than front it possibly would not be balanced. Also it is not mentioned enough. If you install a dual circuit master cyl.. The pedal must completely bottom the piston in the master cyl. before the pedal hits the floor. Test this without fluid. If the pedal bottoms on the floor before the piston, your safety brake system won't work.
This is a timely post as this is the next phase of my project as well. I have been researching the question and i am equally confused so i am watching the post with interest. I am also under the floor with the MC, I am told that you need a 10 PSI residual pressure valve between the MC and the rear brake cylinders to prevent ****ing air into the MC when the pedal is released? Don't quote me on that, I may have that screwed up. And I heard that to allow the rear brakes to work first you need a hold off/metering valve in front of the MC? Maybe a disc brake application but I know that I heard it somewhere.
DRUM BRAKES FRONT AND REAR WITH MASTER ON FIREWALL OR UNDER FLOOR drum/drum, firewall or under floor Drum brakes require a 10 lb. residual pressure (RPV10) to counteract the spring tension in the drum system which tends to pull the shoes away from the drums. This will give you a longer pedal travel and "spongy" brakes. The residual valve holds a pressure keeping the shoes near the drums giving a higher firmer pedal. Also required a metering valve (PVM) to the front (the metering valve prevents nose dive).
Residual valves prevent air from entering the drum brake wheel cylinders during release, needed on all vintage drum brakes, but are a good addition with any drum brake. Metering was only used with some disc/drum systems.
DISC BRAKES FRONT AND DRUMS REAR WITH MASTER UNDER FLOOR disc/drum, under floor The best way to plumb a disc/drum system when the master is under the floor is with a combination valve (PV2) and then a 2 pound residual valve (RPV2) to the front which is needed to prevent fluid from flowing back from the calipers into the master. We also recommend the addition of a 10 lb residual valve (RPV10) to the rear drum brakes.
Sorry hotroddon, the above is total BS. I know where you got it from, and is similar to one or two other brake suppliers who sell stuff but don't have a clue how they work. This has been discussed many times in the past.
Virtually all OEM M/C new or rebuilt come with 10 lb. residual valves installed in the out ports. These are little rubber cones that prevent the brake fluid from rushing back into the M/C when the pedal is released. If you use a after market M/C from a company like Wilwood, then you must put the appropriate residual valve in line. Because of the heavy springs in a drum setup, the shoes walk away too far from the drum unless some fluid pressure is kept in the line. Disc brakes tend to stay where they ae driven, therefore only a 2 lb. residual valve is required in these lines. It is maintained that valves are only necessary when the M/C is below the floor but it is a good idea to use them when ever. A proportioning valve is adjustable to balance brake application between the front and rear brakes. If it is a heavier car and about the same size tire all round, then there should be no need for the proportioning valve, but using big-littles or a very light car, the valve will prevent the rears from locking up. If your M/C comes with residual valves installed and you can see them sitting just inside the out ports, they must be removed for disc brakes. This can be dome easily by turning a drywall screw into the rubber valve and pulling it out. You can then install that 2 lb. residual valve in line again as close too the M/C as possible. And by the way, brakes are not drivel. Install what you want, but just make sure the installer is qualified. Warren
Warren, The only master cylinders that had internal residuals were for drum brakes, and they were not all 10 psi. That is strictly an aftermarket value. Modern disc brakes never needed or used residuals, because of the high firewall master cylinder location on disc braked cars/light trucks. The ONLY time a residual is used with discs is when the master is below the floor and lower than the calipers, and then ONLY a 2 lb valve. Normal drum brake (total) shoe-to-drum clearance is .025"-.030", and the last thing you want is to have the shoes "floating" around and not firmly seated against their anchor(s). Because of the heavy (strong) drum brake return springs, NO WAY can a 10-20 lb residual valve overcome the return springs, and NO reason why you would want them to. Proportioning came about with disc/drum systems, because of the higher pressure requirements of disc vs drum brakes, and the need to keep the rear brakes from locking during higher decel braking to retain good vehicle control in ever toughing DOT braking/handling requirements. Tires, along with static/dynamic vehicle weight, CG, wheel base, engine weight/location also play a role in prop valve operational value.
Bob I tried to keep an overview as brief as possible. I have a friend who rebuilds M/C and they put the 10 lb. rubber valve in every port whether single of double. That is the only reason I cautioned about removing it. I agree with the disc brake not needing the valve if it is high but better to err on the side of caution. Again with the proportioning valve, I have used or not used them in drum/drum, disc/disc and mixed dependant upon the vehicle. I like to try without first and see where it goes. Brakes are a very complex subject and the most important thing is be sure you are qualified or have a qualified person setting them up. Safe and Merry Christmas Warren
Warren, The only residuals that should be installed in a master cylinder are in the drum brake port(s). Using a 10 lb residual with a disc brake will very likely cause a run-away (self applying) brake!
It would be nice to see some real information here along with a good diagram. Nothing posted here so far strikes me as correct. A lot of misinformation and opinion.
Blue One Diagrams enough for you? As a Canadian responding to a Canadian, I am really embarr***ed with this thread and your at***ude. I entered 'brake systems hot rod' into Google and got up about 200 diagrams of every possible application. No more drivel. I'm sure Texag09 got his answer. Bob: No where in either of my postings did I state that 10 lb. residual valves should ever go in disc brake lines. Sorry if what I wrote could be mis-interpreted. Warren
Larry, Any drum brake needs a residual, any no matter what. Without it, drum brakes will **** air. Any master cylinder under the floor needs residuals to prevent gravity from ****ing fluid down hill. Are the residuals in the master for drum brakes enough when the master is moved below the floor , I don't know that but its just as possible as not. Get the residuals as close to the master as you can, sometimes you just can get immediately after.
Also to muddy the waters more, make sure you check your master BEFORE installing it for residual valves. I use a paper clip inserted into the port and you'll feel a little spring back tension if it does have the valve. Not all reman masters are the same, I bought 2 same part number (same brand) masters a few months apart and one have res valve while the other didn't. I use res valves (drum or disc for underfloor masters) and an adjustable prop valve on the rear, ALWAYS use good quality parts as cheap ones will leak....I've had very good luck with SSBC stuff, not so much with wilwood or right stuff. I also try to size the new master to the brakes I'm using original master bore, to keep the pedal feel in range. Use real brake line, good line clamps, armor shield can be bought in bulk now, adapter master nuts can be bought and always try to keep the fittings to a minimum to reduce places to leak. And yes, the res valves go as close to the master as possible. Lastly, look at pictures of the vehicle your using the master from and note which port goes to the front brakes and which to the rear.......obviously you'll know on a disc/drum master.
My at***ude Warren ? Give me a break. These threads typically get so filled with contradictory information that it's hard to figure out what or who is right. Diagrams ? The diagrams you posted are easily available when you search. Anyone with even limited intelligence can do that. These diagrams still do not address the initial question for a DRUM/DRUM system. In case you didn't notice they are all for disc/drum combos. Now they may work by just subs***uting drums for the front along with the required 10 lb. residual pressure valve in the system ,but it would be nice to know for sure if that is the only difference. For instance do you still need the adjustable proportioning valve as well ? You will find several different answers for that one. Larry
Build the system, ( all drums, then use the 10 psi residual's), and test it. You'll figure it out real quick if a proportioning valve is needed. If so, add an adjustable one on the rear................................It's called "tuning"..............
Wow........How can you run a under the floor M/C , front disc/ rear drum, without running a "back off" valve,(metering valve) between the front two disc brakes, . Without the "back off" -metering valve your front disc brakes will lock up before any pressure will engage the rear drums. Also running a 10 psi residual valve on the back line and 2 psi residual valve on the front line to keep pressure in the lines. On my '30 coupe , drum/drum, with a 70's chevy truck M/C, under floor, I have two 10 psi residual valves off both both lines....stops great and straight.
Simply not true. Metering, or "hold off", was not used on all production disc/drum systems, and is the one valve I do not use on any custom brake system, including my own. Their purpose was to allow the rear shoes overcome their return springs and engage the drums about the same time the disc pads touched the rotors, providing more even braking on some vehicles, depending on suspension/ch***is design. But early rear lock can also be the result, especially on lo/co surfaces and light load conditions. You really need to install a dust boot on that master cylinder, to keep water/dirt from getting into the bore. Merry Christmas.
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