The Stovebolt Site Forums The Shop Area Engine Shop Dual Master Cylinder Question.

I've searched the archives on master cylinders and have not really found an answer to my questions. When I switch to a dual cylinder, will I have to access it from under the truck to top it off or when I am bleeding the brakes or is itm still accessed through the floor? Also in one of the old threads, I read where one company told a guy that the dual and bracket would interfear with the clutch and could only be used on the automatics. This sounds crazy. Any thoughts? One more question. I have looked at alot of suppliers , and the brackets and related parts all seem the same, most suppliers evn use the same illistration. Is there any difference in the mounting brackets from one supplier to another? Thanks for all of your help.

I have the bracket and master cyl from cpp,on my 51,3100,only problem a little close to the shift linkage on my saginaw 4spd.everything has been working fine over a year now. old navy51..............

I cut a new hole in the floor for access. The MC moved back as I had to fit a vac booster in there too. Some people are using remote reservoirs which would be really nice.

Plenty of room with SM420 transmission.

Don't know about suppliers as I made my own brackets.

I had to do a little messaging on the CCP bracket I bought to get it to fit right. It fits fine with just the master cyl. But when you use the combination valve with it, it interferes. No biggie. I did not use a booster with mine. Stops just fine without it. I cut a bigger hole in the floorpan for access. Just cut a piece of sheet metal to cover with a couple of small screws holding it in. I think there are some pics of the install on my webshots page. Good luck.

I am not going to use a vac. booster, just the mc so I hope it will work ok. I'm not sure as to what trans. I have, the old original 4 speed. Would this be the sm420? Anything else I should know before I start the switch over? Thanks

Figure out whether you are going to go with metering valves/residual valves and proportioning valve or a combination valve and residual valves.

Must have residual valves when the master cylinder is lower than the wheel cylinders, like when you are going up hill and down hill...

Master cylinders that remote reseviors can be hooked up to are all over the junk yards. The ones I'm thinking of are the ones that have plastic resevoirs plugged into the two holes on the cylinder itself. The problem I havn't solved yet is where to get the caps/plugs with hose mounts to cap the master cylinder and run lines to a remote cylinder the firewall and that way not have to pull up my floor mat, padding, insulation and sound deadner, or cut holes.

Any ideas on where to get the caps with male hose fittings?

A buddy of mine has added the dual to his truck and tells me before he finishes his cab and puts it back on he is going to put a battery door on the driver-side floor also to have access. I thought that sounded lik a good idea.

Buddy in AK

Hey Elmer51, just bought my disk brake set-up and the guy at ccp told me the only way to use a booster (any size) was to go w/auto tranny , so I stuck with new double master and kept my pedals. Good Luck on urs. Mike

You'll also have to re-plumb your brake lines.

I have an extra battery cpver I've been planning to install for just that purpose. I've been looking for a floor I could cut the lip from without feeling I was ruining a good floor...

There's all this talk about different kinds of valves to be added , having to replumb the brake lines and everything else. All I really want to do is make my old '51 safer to drive. Is all this nesessary? The parts catalogues give the impression that all you have to do is add the dual MC to the existing brake system and all is fine. They seem to say it fits like a glove. Is this true? Can I buy the mounting bracket and the dual mc and install it without too much pain and have a safer driver??? Thanks

You only need residual pressure valves if you're switching to disc brakes; return springs move the shoes to the limit of the adjusters on drum brakes. Residual pressure valves on disc brakes prevent the pucks from moving beyond the runout of the discs so they don't have far to move when the brakes are applied.

There is nothing wrong with just keeping the original single master cylinder and maintaining the brake system. I haven't heard of many catastrophic brake failures the had no precursors.

Baldy

Booster & original tranny problem:

The problem with installing a 7" or 8" dual diaphragm brake booster in the original stock location is that once the master cylinder is bolted to the back of it the combined length is longer than the space between the tranny and bell housing cross-members. If you've got an automatic or have switched to a t-5 standard you will have eliminated or repositioned the tranny cross member and have no problem. The stock clutch linkage is also in the way but can be repositioned. The CPP kit includes a spacer to move the clutch armature out of the way, I'm not sure about others.

ADDING VALVES AND RE-PLUMBING BRAKE LINES:

Baldy is right that valves are only required in certain circumstances, though they are probably reccomendable always. There are three basic types of valves involved in a brake system: A metering valve, proportioning valve and residual valve.

The proportioning valve sends a different percentage of the hydraulic pressure to the front and back, since disc and drum brakes require different amounts of pressure.

The metering valve delays sending pressure to the front brakes for a bit to allow the back to start braking first.

The residual valves maintain a low level of pressure in the brake lines so that, as baldy says, the pucks or brake shoes/pads are close to the drums/discs and ready to clamp down, and also to keep the disc brake calipers from opening up beyond where they should. These are only required when the master cylinder gets lower than the brake cylinders/calipers. Since our trucks have the master cylinder mounted on the frame at almost the tire level, residual valves might be important when going up or down hill. Disc and drums require different amounts of pressure to be 'at the ready' Fronts need 10 psi and backs need 2 or 4, I can't remember which. You'll need one of each residual valve if you use a disc/drum set up.

There is a thing called a 'combination valve' which is both a metering valve and proportioning valve. Each combination valve is designed for a certain system, ie. disc/drum, disc/disc, drum/drum.

REPLUMBING THE BRAKE LINES:

This is necessary but not to a large extent. Why? Because right now you have a single master cylinder with one line coming out of it and going to all the brakes. If you go to a dual master cylinder, there will be two outlets, one fo the front brakes and one for the backs. This is the purpose and advantage of a dual master because if you develop a leak, lose a wheel cylinder or caliper (leak/failure...) with a single master you lose your brakes. Of course as Baldy says, there are probably some warning signs before hand, but sometimes those get ignore or mis diagnosed, or the failure is sudden. With a dual master, if you lose the back you still have the front brakes because they are on separate hydraulic circuits, which you created when you 're-plumbed' the brake lines.

How hard is it to re-plumb you might ask? Take a look under your truck. You'll see one line coming out of the master cylinder and dividing to front and back brake circuits at a 'tee'. You'll have to eliminate the 'tee' and run two separate lines from the 'tee' to the master cylinder. It really isn't that much work or that difficult.

What if you want to add those residual valves just to be safe? They look like hose fittings and are an inch or two long with two female ends. So, when you are dividing your front and back circuits you could add them between the old lines and new lines, where the 'tee' used to be. Not a big deal and probably worth the minimal investment for the valves ($20 total, maybe).

What about buying the bracket kit and finding a master cylinder at a parts house? Thats your call.

Where can I get the master cylinder braket, or kit, or a booster, master and bracket kit? Lots of people sell them, including jim carter, chevy duty, brothers, CPP, ECI. ECI's webpage lists the original applications they use the master cylinder/dual diapraphm master from. http://www.ecihotrodbrakes.com/master_cylinder_systems.html

What about accessing the dual master or booster and dual master under the floor? There are a variety of solutions. Some people drill another hole beside the existing one and put in a second plug just like the original when going with the dual master. Some people use a remote master they put under the hood. Others cut a hole to see the master and check the level. The kits I've seen come with a squeeze bottle and right angle hose cap to be able to fill the master from beneath the truck after checking it by dipping your finger, and thereby not cut the floor at all.

Brother's has a nice technical article with pictures about installing either just a dual master or booster/master combo.

http://brotherstrucks.com/tech/tech...%20DUAL%20MASTER%20CYLINDER%20CONVERSION

CPP also has instructions and pictures, but not as detailed.

http://www.classicperform.com/Store/1947_59_Trucks/4756MMK2.htm

PS- Combination Valve-

I believe many combination valves also include a sensor to indicate when the hydraulic pressure drops, which is an indication of a low fluid levels caused by a leak or failure. Probably wouldn't be hard to wire up an indicator light to the dash or modify the instrument clusters to add an innocuous light for that purpose if you decided not to cut the floor but were worried about fluid levels.

You can use a combination valve with either just a master or a master/booster combo.

Also, an older hotrodder I know used a dual master and different sized lines to the front discs(smaller) and rear drums(larger) on his '40 chevy coupe instead of using a proportiong valve or metering valve. He did use a residual valve to the front but not the back. I would think carefully about that approach before using it since I don't know anything about it beyond having heard of it, and the cost of swapping all the lines versus putting in valves might not be much different.

On the 1/2-ton Advance Design trucks I've dealt with, the brake plumbing is a little different than described above.

The master cylinder has two outlets. One feeds only the left front brake cylinder. The other feeds a Tee on the right, just behind the bellhousing crossmember, which splits to the right front brake cylinder, and to the hose feeding the two rear brake cylinders.

I ran all new lines so as not to be surprised by a failure later...

Most drum brake master cylinders have a residual valve built in to hold a little pressure against the brake springs. I've heard people say they did not use any valves at all but I added residual valves to my mine because the master is lower than the cylinders and calipers.

I used the combination valve from the vehicle I got my rear axle and rear brakes from, and used a disk kit that used the rotors and calipers from that same vehicle.

Seems to work well two and a half years and 10,000 miles later.

Thanks; I cannot thank you guys enough for the explanation you all have given on the different kinds of valves and the reblumb issue. I have a much better understanding of what I have to do now. Is the mater cylinder really lower than the wheel cylinders? This may not be an issue anyway. If I can buy the bracket, Dual MC, and replumb the lines , maybe add the residual valves for good measure , all will be good. Sound good??? Thanks

1951 Elmer,
One more. Yes the m.c. is lower on a 51 than the w.c. To make this easy for you. If you are using disks on the front ask for a 1969 Ford Mustang disk/drum m.c. The proper residual valves are built in. Just make sure you plum the correct one to the front. To tell take a toothpick and stick in each of the exit holes from the m.c. if you feel a little resistance thats the residual valve one. If you buy the Ford m.c. it will save you about $40.00 and you won't have to plum in residual valves. You will also need a new bracket or make your own. None of the brackets I've seen will line you up right so you will have to make up an off set jog to fit the orig floor pedals. you don't need any boosters or porportioning valves. The stock clutch linkage on your truck will clear however as someone else said if you use a saginaw 4 speed the shift linkgae will be tight. All the more reason to use a 5 speed or orig 4 speed. And if you get a ford m.c. you won't have to deal with the residual valves near the m.c. to plumb.