Dual Master Cylinder
by Charlie "Cletis" Hardin
|It takes a leap of faith (and hopefully a good life insurance policy!) to trust your life to ancient, single system brakes! If you'd prefer not to live life that dangerously, it's not that hard to update your truck's single master cylinder to a safer dual set-up. Here's Mr. Easywrench's ace assistant, Cletis, to walk you through the....|
This tech tip will cover installing the dual master cylinder bracket, non-power dual master cylinder and new brake lines. The bracket is available from most of the truck parts vendors. The master cylinder is also but you'll pay at least twice as much as you would locally. Brake lines of various lengths are available locally also. They will need to be cut to length and re-flared. Don't let that scare you off. I'll show you how.
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I used the bracket from CPP and a master cylinder for a mid-1970's Chevy 1/2-ton. The set-up uses the stock brake pedal. On the original set-up, the pedal mounts to the master cylinder. The conversion bracket bolts on in place of the stock master cylinder and the pedal mounts to it.
Start off by removing the old master cylinder and pedal as an assembly. Remove one of the connectors from your brake light switch so the lights don't stay on while you're working. Disconnect the part that goes inside the cab from the outer pedal arm by removing a nut. Once you get the assembly out in the open it will be easier to dis-assemble. Clean up the pedal arm and the pivot pin. I removed all the old grease from inside the pin.
The next step is to install the new bracket. Here's where I ran into the first problem.
The threads in the stock nutplate were fine thread -- 7/16-20 -- and the supplied bolts were coarse -- 7/16-14. Now the easy way out would be go to the hardware store and buy new nuts. But that's 15 miles away and nuts would be hard to start and get a wrench on. So I built a new nutplate from 1/4" steel.
You may want to buy the new nuts and try to get a wrench on them. But if you want to build your own, here's what I did. I found that piece of stock in my scrap pile. I was going to cut it down but decided the extra length would make it easier to start the bolts. Using the stock nutplate for a template, I centerpunched the hole locations. Then drilled out the holes with a 3/8" drill and tapped them with a 7/16-14 tap.
Here is the bracket installed. You can see the new nutplate sticking out behind the bracket.
After you get it bolted down, you can install the pedal. Here's where you'll run into the next problem. The hole in the keeper for the pivot pin will have to be elongated. Don't forget to grease the pivot pin.
The next step is to temporarily install the new master cylinder. It will have to come out again later to be bench bled. But for now, we want it dry so fluid won't be leaking out while we build the new lines for it. I know, you could probably get by using the old lines. But for how long? The reason we went with the dual master cylinder was for safety, right? So let's go with new lines. You probably need new hoses too. I went one step further and installed new wheel cylinders and brake components, too but I'm not going to cover that here.
OK, so why build new lines when you can buy them pre-bent from the vendors? Besides being more expensive, there are other considerations. For one thing, the pre-bent lines are not going to mate up to your new master cylinder. For another, the 1956 is plumbed with one run going only to the left front brake and another run going to the other front and both rears. I don't want my dual cylinder plumbed that way.
I have a 1959 parts truck and it is plumbed with one run to both front and another run to both rears. I don't know what year the change was made but if your truck is plumbed like this, you could probably use the pre-bent lines and just build some extensions from the new master cylinder to the ends of the pre-bent lines.
|TOOLS REQUIRED||TUBING REQUIRED|
The double flare tool should have instructions but just in case, I took a few pictures of how to use it. The file is to de-burr and slightly chamfer the outside of the cut tube. The rotary file is to do the same to the inside of the tube. Most of the bends I made by hand, using wide sweeping bends. I used the bender when I had to make small radius bends.
The 60" tubes came off the master cylinder. You will have to cut the least amount you can off the ends that go into the master cylinder and put the large threaded nuts on and re-flare. The one going to the rear brakes will cross to the right side of the frame where the stock line did but instead of connecting to the tee, it will connect to the 51" line going to the rear hose with the 1/4" union. The tee that was on the right side of the frame will be moved to the left front of the frame. I enlarged an existing hole for it. The other 60" line goes to it. The 12" line goes from the tee to the left front hose. The 42" line goes from the tee to the right front hose. I ran it along the aft edge of the front crossmember. I couldn't find a 42" line, so I cut one from a 51" and re-flared it.
The 3/16" lines go on the rear end housing. I cut mine from stock I had left over from another project. I got the lengths from the Master Parts Book. The 21" one is actually a little long. I don't know what lengths you'll find available. You might have to buy longer and trim them.
Now go to work bending and installing lines. Put a small amount of brake fluid in a separate container and brush a dab on the threads and flares before assembly. You can use the existing clips to hold the lines to the frame. Install everything finger tight first then go back and tighten.
After you have all the lines installed and tightened you can now remove the master cylinder and bench bleed it. Instructions should come with the master cylinder. If you use the rod that comes with the master cylinder, remove the locking clip from it first. Here's a tip to make bleeding easier and less messy. Cut the master cylinder tubes off a GM parts car and use them to bench bleed. After bleeding, pull the tubes out of the reservoirs and re-tighten the tube nuts with the tubes higher than the fluid level. This will prevent the fluid dripping all over you as you re-install the master cylinder.
Re-install the master cylinder and connect the lines to it. Now is a good time to re-connect the wire to the brake light switch you forgot when you installed the pedal.
Next you need to connect the plunger rod to the brake pedal. This is where I discovered another problem with the CPP bracket kit hardware. The bolt they supplied was too short. Using it would have caused the plunger to enter the master cylinder at an angle. Not only that, the bolt would wobble in the pedal hole. Not acceptable.
I had to make that trip to the hardware store after all. I picked up a 2" long 3/8-16 bolt, a nut and lock washer, all in Grade 8. I used the supplied washer and spacer on opposite sides of the rod end. I put my new nut and lock washer on one side of the pedal and the supplied nyloc nut on the other side. Now the bolt is tight on the pedal and the plunger goes straight into the master cylinder.
All that's left now is bleeding the lines. I'm assuming everyone knows how to bleed brakes. Start by cleaning all the connections to make it easier to spot leaks. You'll need some way to add fluid to the master cylinder. Some people buy an extra hole plug for the floor board and cut another hole. I have a little squeeze bottle that allows me to add from underneath the truck.
Start with the brake closest to the master cylinder. In this case that's the left front. From there go to right front. Then right rear and left rear. Check the reservoir often. It doesn't take many pumps to empty the small side. Don't ask how I know.
Once you get the system bled and there are no leaks, pat yourself on the back then take her for a drive. You'll know the job was done right because you did it yourself.
1953 Chevy 6100
Bolter # 1113
Parker County, Texas
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v. April 2007
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