Master cylinder question
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Laughing Gas
Joined: Sep 2008
Posts: 966
Likes: 26
From: Missouri
Thank you all for the information. I will put all of this together and try to decide which way I want to go. Either way I am going to put on a dual MC. Where does the brake light switch hook up at?
Cargo Master
Joined: Feb 2008
Posts: 2,793
Likes: 128
From: Windermere Valley,B.C. Ca
Senior User
Joined: Jun 2007
Posts: 151
Likes: 0
From: Woodinville
The differences between drum brakes and disk are simple. A drum brake has two "shoes" that are anchored to the backing plate and are forced against the inside surface of the drum by hydraulic pressure. Between the shoes at the bottom of the setup there is some sort of either a self-adjusting or manual adjusting arrangement. The reason for the adjusters is that as the shoes wear you would have to push further down on the brake pedal to stop so keeping the shoes close to the drum is a good idea. Because of this arrangement of shoes and anchor points a drum brake has a tendency to "self energize" What this means is that as the shoes are pushed against the drum they try to wedge against the drum because of the rotation of the drum. If you want to see what they feel like with no self-energizing action then go fast in reverse and hit the brakes. They will not stop as fast and you will have to push harder on the pedal.
Disk brake calipers do not have the geometry to "self energize" and thus need extra pressure. There are two ways normally used to get that pressure. The first is leverage and this can be done a few ways but generally it is made as simple as possible for obvious reasons. The placement of the pushrod in relation to the pivot point on the brake pedal arm is a good start. And to a point this works but normally is not used because you need X amount of pedal travel to do the job but you only have so much room in the cab before the pedal hits the floor. So the mechanical advantage is usually adjusted with the inside diameter of the master cylinder. Smaller bores make for more system pressure as larger bores make for less system pressure. Couple this with the bore of the wheels cylinders and caliper pistons and you have a fluid system setup to multiply the force you use on the pedal to stop your truck.
The piston in a drum brake is pretty close to the same size as the master cylinder. The piston in a disk brake caliper is usually twice the diameter or more of the master. Where a drum has adjusters to keep the shoes close to the drum a caliper has a piston that pushes out and stays out. If you ever wondered why the brake fluid chamber is larger on the disk side of a master cylinder here is why. In order for disk brakes to stay adjusted the pistons continually move out as the pads wear and stay out so the fluid does not return to the chamber as it does with drum brakes. So more fluid is needed in the disk brake side to keep up with the pads wear. Because the drums have a mechanical adjuster the pistons only need to move a small amount and then return. There is a small amount of spring back in a disk brake system from the drag of the seal on the piston. This is just enough to give the disk free movement when the brakes are not applied.
Now if you want to run manual disk brakes you will have to adjust the master cylinder bore size to get good braking action without having to really push hard on the pedal. You will also have to adjust the size of the wheel cylinders in the drums for the same reason. You want the braking force divided from front to back because 70% of your braking job is done up front. Later you can add a "booster" to that system as they did with some of the Ford trucks of the mid 60's. My 1969 has a "booster" that is smaller in diameter than a full out Power Brake setup. If I disconnect the "booster" there is little to no difference that I can feel in the brakes unless I am running fully loaded. The booster assists the brakes in this case and is not a full Power Brake system. Now with a full out Power Brake setup you will notice a breath taking difference when you disconnect the power booster as in you will be on that pedal with both feet praying you will stop.
My Ford Mustang had a disk drum setup with no booster and it worked just fine but believe me changing the master cylinder out for the wrong one about got me killed. The new one had a larger bore and was for a Mustang with drum/drum brakes. As a result the first time I came off the freeway at speed I felt like I was going to pull the steering wheel off because I was on the brake pedal so hard. I took the ditch rather than the police car that was in line in front of me. He looked at me with that "oh geez… not another stupid kid" look. After I explained to him why I took the ditch rather than his rear bumper he told me that the parts place probably gave me the wrong master cylinder. That was my first experience with master cylinder bores and brake system pressure and so on. Brake system questions are not easy to answer and even harder to work out from scratch, let the manufacturer work it out then you just grab a setup and use it.
Unless you have lots of time to change out master cylinders and tinker with proportioning valves and so on you may as well do your brakes Once and Right the first time. Where the brakes, steering and wheels are concerned skimping is not a good idea and is down right dangerous. Skimp on the paint or the bumper or the radio or the seat but please don't skimp on what is going to keep you alive in a pinch. Where brakes are concerned you may only get one chance with no do overs.
Your best bet is to figure out what you want in brakes and go grab all of the brake setup out of the same vehicle. I.E. a 67 or so half ton ford with disk brakes up front.
Because of the way a master cylinder works I have never seen one with a step bore, meaning two different inside diameters in the same hole. Because manufacturers tend to try and keep costs down so they can charge you more, they would use the same casting for either drum/drum or drum/disk, the only difference between the two would be valves which is all internal and plumbing sizes. Nothing really different on the outside but they are different on the inside.
As for a brake light switch, you can get one that goes in the brake line and is activated by the pressure of the system. I would not advise an open brake switch under the truck because of water, which would short out the system.
Cyrus
_____________________
My Grandpa told me once that you have to learn by the mistakes of others because you will NOT live long enough to make them all yourself.
Disk brake calipers do not have the geometry to "self energize" and thus need extra pressure. There are two ways normally used to get that pressure. The first is leverage and this can be done a few ways but generally it is made as simple as possible for obvious reasons. The placement of the pushrod in relation to the pivot point on the brake pedal arm is a good start. And to a point this works but normally is not used because you need X amount of pedal travel to do the job but you only have so much room in the cab before the pedal hits the floor. So the mechanical advantage is usually adjusted with the inside diameter of the master cylinder. Smaller bores make for more system pressure as larger bores make for less system pressure. Couple this with the bore of the wheels cylinders and caliper pistons and you have a fluid system setup to multiply the force you use on the pedal to stop your truck.
The piston in a drum brake is pretty close to the same size as the master cylinder. The piston in a disk brake caliper is usually twice the diameter or more of the master. Where a drum has adjusters to keep the shoes close to the drum a caliper has a piston that pushes out and stays out. If you ever wondered why the brake fluid chamber is larger on the disk side of a master cylinder here is why. In order for disk brakes to stay adjusted the pistons continually move out as the pads wear and stay out so the fluid does not return to the chamber as it does with drum brakes. So more fluid is needed in the disk brake side to keep up with the pads wear. Because the drums have a mechanical adjuster the pistons only need to move a small amount and then return. There is a small amount of spring back in a disk brake system from the drag of the seal on the piston. This is just enough to give the disk free movement when the brakes are not applied.
Now if you want to run manual disk brakes you will have to adjust the master cylinder bore size to get good braking action without having to really push hard on the pedal. You will also have to adjust the size of the wheel cylinders in the drums for the same reason. You want the braking force divided from front to back because 70% of your braking job is done up front. Later you can add a "booster" to that system as they did with some of the Ford trucks of the mid 60's. My 1969 has a "booster" that is smaller in diameter than a full out Power Brake setup. If I disconnect the "booster" there is little to no difference that I can feel in the brakes unless I am running fully loaded. The booster assists the brakes in this case and is not a full Power Brake system. Now with a full out Power Brake setup you will notice a breath taking difference when you disconnect the power booster as in you will be on that pedal with both feet praying you will stop.
My Ford Mustang had a disk drum setup with no booster and it worked just fine but believe me changing the master cylinder out for the wrong one about got me killed. The new one had a larger bore and was for a Mustang with drum/drum brakes. As a result the first time I came off the freeway at speed I felt like I was going to pull the steering wheel off because I was on the brake pedal so hard. I took the ditch rather than the police car that was in line in front of me. He looked at me with that "oh geez… not another stupid kid" look. After I explained to him why I took the ditch rather than his rear bumper he told me that the parts place probably gave me the wrong master cylinder. That was my first experience with master cylinder bores and brake system pressure and so on. Brake system questions are not easy to answer and even harder to work out from scratch, let the manufacturer work it out then you just grab a setup and use it.
Unless you have lots of time to change out master cylinders and tinker with proportioning valves and so on you may as well do your brakes Once and Right the first time. Where the brakes, steering and wheels are concerned skimping is not a good idea and is down right dangerous. Skimp on the paint or the bumper or the radio or the seat but please don't skimp on what is going to keep you alive in a pinch. Where brakes are concerned you may only get one chance with no do overs.
Your best bet is to figure out what you want in brakes and go grab all of the brake setup out of the same vehicle. I.E. a 67 or so half ton ford with disk brakes up front.
Because of the way a master cylinder works I have never seen one with a step bore, meaning two different inside diameters in the same hole. Because manufacturers tend to try and keep costs down so they can charge you more, they would use the same casting for either drum/drum or drum/disk, the only difference between the two would be valves which is all internal and plumbing sizes. Nothing really different on the outside but they are different on the inside.
As for a brake light switch, you can get one that goes in the brake line and is activated by the pressure of the system. I would not advise an open brake switch under the truck because of water, which would short out the system.
Cyrus
_____________________
My Grandpa told me once that you have to learn by the mistakes of others because you will NOT live long enough to make them all yourself.
Thread Starter
|
Laughing Gas
Joined: Sep 2008
Posts: 966
Likes: 26
From: Missouri
Is a remote fill MC different from a regular MC or is it just a special cap that fits on the MC that the remote fill connects to? Question for those that have upgraded their brakes with MC under the floor, how do you fill the MC if you do not have a remote fill? Like to see pictures of the remote fill installed.
Mountain Pass
Joined: Aug 2006
Posts: 216
Likes: 18
From: Central NC
special cap...
my brake kit came with a small bottle with a 'J" ? shaped tube on it...
it works... squeezing the fluid into the MC...
I am lucky enuff to have a lift, so it is relatively easy... and just 'how' often do you need to add fluid??
the master cylinder itself is no different between the remote fill and 'typical'...
my brake kit came with a small bottle with a 'J" ? shaped tube on it...
it works... squeezing the fluid into the MC...
I am lucky enuff to have a lift, so it is relatively easy... and just 'how' often do you need to add fluid??
the master cylinder itself is no different between the remote fill and 'typical'...
Elder User
Joined: May 2006
Posts: 572
Likes: 0
From: Sacramento area
pappys53
If your concern is, if engine fails and you will lose all vacuum, the answer to your concern is a vacuum tank. IMHO I don`t think losing vacuum because of an engine failure is of great concern, there will still be unused vacuum in booster.
I have disc/drum in my gallery. Good luck whichever way you go.
Gary
If your concern is, if engine fails and you will lose all vacuum, the answer to your concern is a vacuum tank. IMHO I don`t think losing vacuum because of an engine failure is of great concern, there will still be unused vacuum in booster.
I have disc/drum in my gallery. Good luck whichever way you go.
Gary
