On my dual mastercylinder I have two resovors, one large one small. I**** U me large is for drum brake small for disc. I the airforce an old E9 said "never****ume It'll make an**** out of you and me" I'm looking for the right way to plumb. Terry aka dirt t
yup, as the pads wear, fluid moves from the master to the calipers, and there has to be enough that it doesn't run low.
Actually fluid displacement. When pads wear away fluid collects in the calipers and empties the master reservoir.
Just to stir the pot! Let's take the case of the commonly used Corvette master which has both reservoirs the same size. Now does it matter?
I've seen 50/50 on here, I personally like to plumb the master for what it originally came in. So I used a Chrysler master from a '65 car, I look up the line routing (ports front or rear) and plumb it that way (same with dual disc masters). http://www.britishv8.org/Articles/Tandem-Master-Cylinders.htm To the original post: Large pot = Disc Small pot = Drum
Even from the outside you can see the difference. Front is muffin belly and rear is straight walled at tappers back.
Every car I've seen has the bigger reservoir hooked up to the disc brakes from the factory. And the smaller reservoir for the drums should have a residual valve in the outlet.
I suppose the front brakes do about 75% of the actual braking so they need a bigger reservoir along with then pad wear issue?”l
The front brakes usually have larger diameter pistons (because they do more braking, as you said), so they can hold more fluid, is why they have larger reservoirs.
It's more about the available usable pad thickness compared to a brake shoe. PS. Squirrel is quicker and takes time to explain it better!
Reservoir size only matters if you don't check the fluid level till the brakes need replacing. Who on here gonna do that?
If you have disc brakes with a large reservoir and as the brakes wear you keep filling the master cylinder full then when it's time to replace the pads and go compressing the caliper pistons your going to have brake fluid everywhere. All that extra brake fluid you've been adding over time will have to go somewhere and since you always keep it full it's going to be spilling over the reservoir and all over the firewall, frame and floor. Thus this why most master cylinders on the disc side have large reservoirs, to hold enough fluid to brake pad replacement then you can press the caliper pistons back in and have a full reservoir again. .
"IF". You're doing your brake servicing correctly ,you open the bleeder screws before compressing the calipers thereby draining the excess fluid . After service is performed while bleeding the system , you flush the system as part of the brake service .
OK. I was wrong. There is a slight difference in the size of the reservoirs. But you missed the point of the question. So why do they have 2 different sized reservoirs? The question is: Is it just the size of the reservoir that determines which is front? Or is there something internal that says this reservoir is the front? My T was plumbed with the big res to the rear drums, smaller to the front discs. Just because it made for neater plumbing. The brakes worked just fine. I read so many of these damn threads that I decided one day to swap ends with the plumbing. Quick process. Absolutely no difference in braking. My experience says it makes no difference at all unless you are leaking fluid and not checking. In which case you are going to lose all your fluid eventually. No matter how big your reservoir is. You better fix that!
The size of the reservoir is based on how much fluid the caliper will hold when the pads are completely worn out....if the rear calipers hold less than the fronts because the pistons are smaller because they need less braking force, then the reservoir for the rears can be a bit smaller than that for the front. It's pretty simple.
Twenty percent is not slightly. If you suddenly lost 20% of your front braking power, you would have a car accident. The front calipers on a Corvette have a larger total piston area than the rears, and the pads will also wear faster. More fluid volume is required to compensate for both of those conditions. This style of master cylinder is popular because it is over-the-top of the requirements of almost all systems.
You guys are all missing the point. I am not debating that a different sized cylinder at the brake, be it a drum brake cylinder or a disc brake caliper, that the reservoir needs to be sized accordingly. That's pretty obvious, but a 20% reduction in the size of the master reservoir will not result in a 20% reduction of braking power. I have never seen this answered. I asked it before, but the conversation focused on the volume of the reservoir. Is there something internal to the master, such as maybe port positioning or something?, that says one of the reservoirs must be the front brakes, besides reservoir volume?
A reservoir only stores fluid. If you wanna know more about the front and rear “circuits” of a dual master stop say reservoir.
Yes Take a look at the path-of-force that begins at the pushrod tip. You will see that the pushrod pushed the first, or primary piston. That piston is not connected mechanically to the secondary piston. There is a spring in-between, but that is not there to apply braking force, except if the primary circuit has been lost (and the spring goes "full-block"). Otherwise both springs are return springs. What applies force to the secondary piston is the presence of incompressible liquid (brake fluid). By varying the length of the pistons, and the position of the outlets, a master cylinder can be "timed" to bias the rear brakes. There are designs that can favor either end. Mopar, for one, did like to go the opposite route of many other OEM's. Now let's take the aforementioned "Corvette-style" master cylinder: Careful examination of the rear outlet places it at the division wall between the reservoirs, and the front outlet far ahead of the end of the leading-edge of the front reservoir. These dimensions are not random accidents. Every single dimension has been carefully calculated. Beyond that, there are numerous caliper designs, the most famous (or infamous) here is the GM Metric "low-drag" caliper, which has angular seals which are designed to pull the piston away, retracting the pads from the rotor. In the case of calipers like that, it is imperative that not only the correct "quick take-up" master cylinder be used, but also that the plumbing be correct. Switch the lines in that instance and you will likely have a head-on collision with the person that was previously following you, and a lot of explaining to do, to that driver, the police, and your insurance company. There are other examples, and that does not even touch diagonal braking circuits found in many European cars.
When the brakes are applied, fluid begins to move from both lines, front and rear. The fluid from the rear section has dual functions. It activates the rear brakes and it moves the front (secondary) piston forward, applying the front brakes. For the initial part of the stroke, until the rear friction surfaces have made contact with metal, the path-of-least-resistance is to move the rear braking mechanism, rather that the front (secondary) piston, although that does move too. When metal contact has been made, and rear braking is underway, the next path-of-least-resistance is to move the front piston, applying the front brakes. When I had that module at university, it took about 500-pages to fully describe it, so now you're down with the discount.
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