How about the hoses, new or old? They can play with you if they're old. Dirt can get stuck inside the hose or they can swell up during pressure.
ran the same speedway master years ago with the exact same problem you are having. swap out with a different master!
I dont know if you have the right m/c as if it is a drum/drum one the resivoirs should be the same size. that one in the pic looks like for a disk brake syst
The fact that you are getting a firm pedal on the first pump, although the travel is too far and then you have a firm pedal at the second pump would indicate a master cylinder that is too small. If there was air in the system you would not get a good pedal at all as you would just keep compressing the air. The master does not have to have the same size resevoirs or cylider bores as these would be adjusted to give slightly different pressures on the front and back systems, you don't want your rear brakes locking. I would look at a different master, try to talk directly with a company that makes them, they will ask the size of the wheel cylinders so that they can work out the correct sizes of bores in the master, if the residual bores are built in you don't need them, if you go with a master with the same size bores a proportioning valve would be recommended.
Did you check to make sure the check valves were not in the MC? Two checks in line may cause a hydraulic issue
If the shoes are adjusted so they are dragging on the drums, try a Bench Bleed on the car. Loosen closest wheel bleeder and remove the pedal rod and use a long stiff screwdriver to compress the MC a couple of times. Make sure you bottom the piston in the MC. Fixed mine when the Bench Bleed off the car did not.
Speedway says no valves built in, and the listing for the part says Drum/Drum or Drum / Disc, I guess that is why no residuals built in, so its very universal. So if my bore is too small, and I want to get one at local napa dealer, what bore do I need, I have heard 1 1/16" on here, is that really enough to mak ea difference from 1"?
amen....to eastwood............its not rocket science.stop trying to invent the wheel.no residuals.....basic master for drum system...at least 1 1/16. listen to the master n not speedway .
True, you'd always have a somewhat spongy pedal if there was air in the system. I'm in the camp that thinks your M/C is too small of a bore. Some of the mid-60's mopars had large-bore drum/drum M/C's, might be another option for you. I think the 66 Charger I had was a 1 1/8 bore.
I never owned an old car that came with them either. They are a modern misconception, or at least I think they are I could be wrong. I am going to go with the wrong cylinder bore or actuation rod adjustment.
Uhhhh - sounds dumb but are the wheel cylinders on the right sides. A brake shop put two left callipers on my car once and it created hell because one of the bleeders was down instead of up. It was many trips back before somebody picked up on it. ...just a maybe.
Toss the residual valves and check what size front wheel cylinders you have. 42-48 Ford front brakes came with two different size wheel cylinders. If your lucky you have the larger ones and can switch to the smaller. Keep the system as close to stock as you can. Nobody spent more money developing parts as the original manufacturers. Dont try to reinvent the wheel and dont listen to people that think they can.
I had exactly the same problem. A very small lengthening adjustment of the m.c. pushrod solved my problem. Worth a try. Good luck.
We're not talking rocket science here. I just converted the mechanical brakes on my '38 to 1940 hydraulics. I had a complete system off a freshly restored '40 chassis. I say freshly restored as the restoration was done 15 years ago, just never driven. Even though things were "new" I didn't want any problems so I replaced all of the software pieces (rubber seals, hoses,etc.). Every thing was ordered from Mac's and installed as per Ford service bulletins. Brakes were bled and adjusted. The car drives and stops like every '40 in good condition that i've ever driven. Frank
When trying to get things working first time on drum brakes,i adjust push rod so it bottoms out at same time as pedal bottoms out on stop or firewall what ever stops pedal.,even before bleeding,I just adjust drums all up=can't trun drums at all=no spring action at all by then,then I bleed them and comeback on shoes dose not happen as I bleeding,you get a hard pedal and clear fuild/no air showing in a clear hose off the bleeders. This has made things EZer 4 me,after it feels real good,I back off the shoe adjust just enough to turn=now you do loss some pedal at that point but have as much as you will ever have. By that time you may find you like your pedal to not be so high,so you can then adjust puchrod tell it is were all is good.
Just had the same problem on my 34 I was running speedway 1" bore m/c with disc's on the front with no problems , changed the front to drums and couldn't get a pedal on first pump just like yours , after various attempts at all different things I changed my m/c to a 1 1/8" bore and perfect brakes . Posted from the TJJ App for iPhone & iPad
Trying to understand brake pedal effort with non power assisted system. Would larger frt wheel cylinders provide more presure to frt shoes, or less? Thanks, Bill
First be sure you are bottoming out m/c when you pump brakes then clamp of rear brake hoses to see if problem goes away,if it doesnt go away move clamp to one of the frontbrake hoses and repeat,to see if you can find the problem. Do your self a favor and dont just keep throwing money at it with out doing some basic diagnostic work.Studie the problem it might take a while to figure it out but that will be the way you get it fixed. you may have a def. wheel cylinder that sucks air by clamping the line you will start to narrow down were the problem is. Thanks Hope this helps.
A larger bore wheel cylinder will result in more pressure on the shoes with the same pedal effort, but if the M/C bore remains the same size the pedal travel will be further due to the additional fluid that is required to fill the larger wheel cylinder.
Give Master Power Brakes, www.mpbrakes.com, 888-351-8781 a call, all they do is hot rod brakes. Their catalog is great!
So, what part # did you use, I will surely try this, it sounds like an exact replica of my issue using same stuff.
Here is some info I found from my research: Mathematical babble? The arithmetic simply equates to the amount of force exerted by your leg times the pedal ratio divided by the area of the brake piston(s). FYI, the typical adult male can exert roughly 300 pounds of force (maximum) with one leg—and that’s a bunch. Something in the order of 1/3 or 1/2 that figure is obviously more comfortable, even in a hardcore racecar. The average manual (non-power boosted) master cylinder requires somewhere between 600-1,000 PSI to be totally effective. Somehow, 100-150 pounds of leg force has to be translated into 600-1,200 PSI. The way it's accomplished is by way of pedal ratio. While changing the overall length of the pedal is possible, it's often easier and far more practical to shorten the distance between the pivot point and the master cylinder pushrod mount location. That's precisely how many racecar chassis shops modify brake pedals. Brake Line Pressure Brake line pressure is a different thing than the force you apply to the pedal. Force acts in one direction and is addressed in pounds. Pressure acts in all directions against surrounding surfaces and is addressed in pounds per square inch or PSI. "Levers" (brake pedals) can be used to change the force. Inside the hydraulic system, the surface area of the piston is what is affected by pressure. Decreasing the bore size of the master cylinder increases the pressure it can build. Pistons in master cylinders are specified by bore size. But there's a hitch: The area of a circle (or bore) is Pi–R-Squared. The area of the piston surface increases or decreases as the square of the bore size or diameter. For example, the area of a common 1-1/8-inch master cylinder is approximately 0.994-inch. The area of an equally common 1.00-inch bore master cylinder is approximately 0.785-inch. Switching from the larger master cylinder to the smaller version will increase the line pressure approximately 26.5% assuming that pedal ratio hasn't changed. As the pedal force or the pedal ratio (or both) is increased, the stroke of the master cylinder is shortened (brake line pressure is unaffected). When the size of the master cylinder piston increases, the output pressure of the master cylinder decreases. A smaller master cylinder piston will exert more line pressure with the same amount of force (pedal ratio) than a master cylinder piston with a larger piston area. There's another catch: Since the brake line fluid pressure is working against the surface of the wheel cylinder (or disc brake piston), increasing the area of the cylinder will increase brake torque. The bottom line is, if the stopping power of a car needs improvement, or if there’s a need to reduce the pedal effort, several options are available: (1) Decrease the master cylinder bore size; (2) Increase the pedal ratio; (3) Increase the wheel cylinder bore size. If the pedal ratio is increased, there will be more travel at the master cylinder piston. If the master cylinder bore size is decreased, the piston has to travel further to move the same amount of fluid. Typically, a master cylinder has approximately 1-1/2-inch to 1-3/4-inch of stroke (travel). The idea here is coordinate the pedal ratio with the bore size to arrive at approximately half of the stroke (roughly 1-inch) in order to make the brakes feel comfortable, and of course, to bring the car to a grinding halt.
Here is another: Going faster creates a need for stopping faster. Efficient braking is based on choosing the right components and matching the proper combinations will result in a brake system that works in conjunction with the specifics of your car, track and driver style. It is highly recommended that you work with your brake company engineer to assist you in building the right combination to tailor a system for your application. Since pad compound, rotors, calipers and master cylinders all work together in relation to car weight, speed and track characteristics, it makes sense to think of your brake system as a package. Each brake component relates to the other braking variables and an individual change may necessitate the need to reanalyze your entire brake system in your effort to achieve a balanced clamping force on your car. A Billet Clamp On Reservoir Mount allows you to mount your brake fluid reservoir at a high point resulting in improved brake bleeding. Remote mounting keeps unwanted heat away from your brake fluid. We contacted long time brake expert Carl Bush from Wilwood engineering to help our readers understand the brake system. While I encourage you to consult your brake company engineer to build the right braking system, I also encourage you to learn how the parts interrelate. With your own knowledge base, education will allow you to better communicate your needs resulting in the best brake system possible. How do you pick the proper master cylinder? Carl Bush: Master cylinders are an integral component in the brake system. They are responsible for sending the correct amount of pressure and balance to the brake calipers. But it must be remembered that they are only one component in a system, and do not function alone. Brake requirements for different types of race cars will vary by component and element. But all systems do carry a common thread. They must allow the driver to stop the car with comfortable leg effort while contributing to the overall handling and performance of the car. How do master cylinders work? Carl Bush: A master cylinder is used to convert force from the brake pedal into the hydraulic pressure that operates the brake calipers. The amount of pressure generated is a function of the force being applied, divided by the master cylinder bore area. A 1” master cylinder has a bore area of .785” inches squared. For every hundred pounds of force applied to the master cylinder piston by the pedal pushrod or balance bar, that master cylinder will generate pressure equal to 100 divided by .785 or 127.4 PSI. By calculating the area in inches squared (bore x bore x .785” for any master cylinder size, you can calculate how much pressure change would be affected by a bore size change. A 7/8” bore master cylinder has a bore area of .6” inches squared. If we apply that same 100 pounds of force to the 7/8” master cylinder, using the formula 100 divided by .6, that same 100 pounds of force from the pedal will generate 166.7 PSI. A decrease in master cylinder bore area produced a proportionate increase in line pressure. This line pressure management becomes a key factor in setting brake balance. Master Cylinder bore size is the element that affects pressure. Jeff Butcher: So Carl provides some great information about how master cylinder size works with your leg effort and brake system. How can we use Carl’s master cylinder bore area math to our benefit? Since my articles try to remove some of the engineering speak and present information into layman terms, I will try to expand on the math that Carl is illustrating. If you read all the way through you will see that the math is easy once you get a handle on all of the terminology. By understanding the basics you will have more data to make informed decisions. Carl explains that a 1” Master Cylinder has a bore area of .785” squared. To get to this number you use the formula for Area which is: Area = 3.14 (Pi) multiplied by the radius squared. So you calculate the radius of 1” bore which is simply half of the diameter which equals .5” (half an inch). The result is that a 1” master cylinder has a radius of half an inch. You then multiply your radius which is a half an inch (.5) by itself so .5” X .5” = .25” or a quarter of an inch. .Multiply .25 X 3.14 (pi) and you arrive at Carl’s .785” area number. Basically, I just repeated what Carl said in an effort to make the math more simple and I bet the barrage of numbers made the calculation more intimidating and confusing? It’s ok – we will get to a simple way to look at the master cylinder math and going through the steps will make the process easier to understand. Another way to explain Carl’s math uses a 7/8” master cylinder as the example. We will do the calculation and show our work to reinforce the math for calculating bore area. Bore = 7/8” 7 divided by 8 gets us the decimal equivalent = .875” The Radius is .875” divided by 2 = .4375” .4375” Multiplied by .4375” (Squared) = .1914” .1914” Multiplied by (Pi) 3.14” = .6” - which is the answer Carl explained above. With the progression towards understanding the math we can do take the steps the easy way. Use Carl’s magic formula of Bore X Bore X .785” (.785 is the magic number that simplifies the above equations as it simply pre-calculates the squared business relating to Pi in advance). So a 7/8” bore is .875” X .875” X .785” = .6” Bore Area. It turns out you can use the number .785” and multiply it by ANY Bore X Bore as the reusable number of.785” is a derivative of Pi and it is a repeatable math number that can be used with any and all bore sizes. So, the complicated math shown relating to Master Cylinder Bore Area can be simplified. Now we have taken another step towards understanding. Bore X Bore X .785” - you can always use .785” in the equation. Let’s check with the Easy 1, 2, 3 method: For an example 7/8” Bore master cylinder the Bore Area math is: Step 1 – Convert the fraction Bore to a decimal by dividing the bottom number in the fraction into the top number. 7 divided by 8 = .875”. 7/8” is the bore marked on the outside of the master cylinder and .875” is the decimal bore equivalent of 7/8” Step 2 – Multiply the bore diameter (our example is .875” by itself which is the same as bore squared. .875” X .875” = .766” Step 3 – Multiply the bore squared result from step 2 (.766) by the reusable number (always .785 with every master cylinder size – you can count on .785 to work every time with every master cylinder size). .875” X .875” = .766 .766 X .785” = .6 .6 is the Bore Area for a 7/8” Master Cylinder! The EASY 1, 2, 3 Bore Area calculation is right here! Our example was for a 7/8” master cylinder. Now you can use the bore size on your car and substitute your actual numbers to come up with your Bore Area, front and rear, by following the 1,2,3 calculation above. Now that we have our Bore area numbers of .6 for a 7/8” master cylinder and .785” for a 1” master cylinder what do we do next? Carl states that a smaller master cylinder bore creates more pressure with an equal amount of force. A 1” master cylinder creates 127.4 PSI as compared to a 7/8” master cylinder which is 166.7 PSI based on your foot making 100 pounds of force at the master cylinder. It is important to consider that the smaller cylinder makes more pressure but the smaller bore will move less fluid. More travel will be needed to make up for the reduction in fluid moved by a 7/8” master cylinder as compared to the larger 1”. Carl explains further in the next section. Utilizing a bolt on caliper mount ensures that your calipers are square to the rotor improving pad wear and braking efficientcy. How do fluid volume and leverage come into play? Carl Bush: While a change in master cylinder bore size affects a pressure change, it also changes the amount of pedal travel realized to add the additional stroke needed to displace enough fluid to move the caliper pistons. This volume ratio plays an important role in the clamping capability of the caliper, and leverage that the driver has to generate that clamping force. The ratio between the caliper and master cylinder is a function of the net effective caliper piston bore area divided by the bore area of the master cylinder. To compare these ratios and do the calculation, you must start with the total piston area of the pistons in one side of one caliper. Going faster creates a need for stopping faster. Efficient braking is based on choosing the right components and matching the proper combinations will result in a brake system that works in conjunction with the specifics of your car, track and driver style. It is highly recommended that you work with your brake company engineer to assist you in building the right combination to tailor a system for your application. Since pad compound, rotors, calipers and master cylinders all work together in relation to car weight, speed and track characteristics, it makes sense to think of your brake system as a package. Each brake component relates to the other braking variables and an individual change may necessitate the need to reanalyze your entire brake system in your effort to achieve a balanced clamping force on your car. A Billet Clamp On Reservoir Mount allows you to mount your brake fluid reservoir at a high point resulting in improved brake bleeding. Remote mounting keeps unwanted heat away from your brake fluid. We contacted long time brake expert Carl Bush from Wilwood engineering to help our readers understand the brake system. While I encourage you to consult your brake company engineer to build the right braking system, I also encourage you to learn how the parts interrelate. With your own knowledge base, education will allow you to better communicate your needs resulting in the best brake system possible. How do you pick the proper master cylinder? Carl Bush: Master cylinders are an integral component in the brake system. They are responsible for sending the correct amount of pressure and balance to the brake calipers. But it must be remembered that they are only one component in a system, and do not function alone. Brake requirements for different types of race cars will vary by component and element. But all systems do carry a common thread. They must allow the driver to stop the car with comfortable leg effort while contributing to the overall handling and performance of the car. How do master cylinders work? Carl Bush: A master cylinder is used to convert force from the brake pedal into the hydraulic pressure that operates the brake calipers. The amount of pressure generated is a function of the force being applied, divided by the master cylinder bore area. A 1” master cylinder has a bore area of .785” inches squared. For every hundred pounds of force applied to the master cylinder piston by the pedal pushrod or balance bar, that master cylinder will generate pressure equal to 100 divided by .785 or 127.4 PSI. By calculating the area in inches squared (bore x bore x .785” for any master cylinder size, you can calculate how much pressure change would be affected by a bore size change. A 7/8” bore master cylinder has a bore area of .6” inches squared. If we apply that same 100 pounds of force to the 7/8” master cylinder, using the formula 100 divided by .6, that same 100 pounds of force from the pedal will generate 166.7 PSI. A decrease in master cylinder bore area produced a proportionate increase in line pressure. This line pressure management becomes a key factor in setting brake balance. Master Cylinder bore size is the element that affects pressure. Jeff Butcher: So Carl provides some great information about how master cylinder size works with your leg effort and brake system. How can we use Carl’s master cylinder bore area math to our benefit? Since my articles try to remove some of the engineering speak and present information into layman terms, I will try to expand on the math that Carl is illustrating. If you read all the way through you will see that the math is easy once you get a handle on all of the terminology. By understanding the basics you will have more data to make informed decisions. Carl explains that a 1” Master Cylinder has a bore area of .785” squared. To get to this number you use the formula for Area which is: Area = 3.14 (Pi) multiplied by the radius squared. So you calculate the radius of 1” bore which is simply half of the diameter which equals .5” (half an inch). The result is that a 1” master cylinder has a radius of half an inch. You then multiply your radius which is a half an inch (.5) by itself so .5” X .5” = .25” or a quarter of an inch. .Multiply .25 X 3.14 (pi) and you arrive at Carl’s .785” area number. Basically, I just repeated what Carl said in an effort to make the math more simple and I bet the barrage of numbers made the calculation more intimidating and confusing? It’s ok – we will get to a simple way to look at the master cylinder math and going through the steps will make the process easier to understand. Another way to explain Carl’s math uses a 7/8” master cylinder as the example. We will do the calculation and show our work to reinforce the math for calculating bore area. Bore = 7/8” 7 divided by 8 gets us the decimal equivalent = .875” The Radius is .875” divided by 2 = .4375” .4375” Multiplied by .4375” (Squared) = .1914” .1914” Multiplied by (Pi) 3.14” = .6” - which is the answer Carl explained above. With the progression towards understanding the math we can do take the steps the easy way. Use Carl’s magic formula of Bore X Bore X .785” (.785 is the magic number that simplifies the above equations as it simply pre-calculates the squared business relating to Pi in advance). So a 7/8” bore is .875” X .875” X .785” = .6” Bore Area. It turns out you can use the number .785” and multiply it by ANY Bore X Bore as the reusable number of.785” is a derivative of Pi and it is a repeatable math number that can be used with any and all bore sizes. So, the complicated math shown relating to Master Cylinder Bore Area can be simplified. Now we have taken another step towards understanding. Bore X Bore X .785” - you can always use .785” in the equation. Let’s check with the Easy 1, 2, 3 method: For an example 7/8” Bore master cylinder the Bore Area math is: Step 1 – Convert the fraction Bore to a decimal by dividing the bottom number in the fraction into the top number. 7 divided by 8 = .875”. 7/8” is the bore marked on the outside of the master cylinder and .875” is the decimal bore equivalent of 7/8” Step 2 – Multiply the bore diameter (our example is .875” by itself which is the same as bore squared. .875” X .875” = .766” Step 3 – Multiply the bore squared result from step 2 (.766) by the reusable number (always .785 with every master cylinder size – you can count on .785 to work every time with every master cylinder size). .875” X .875” = .766 .766 X .785” = .6 .6 is the Bore Area for a 7/8” Master Cylinder! The EASY 1, 2, 3 Bore Area calculation is right here! Our example was for a 7/8” master cylinder. Now you can use the bore size on your car and substitute your actual numbers to come up with your Bore Area, front and rear, by following the 1,2,3 calculation above. Now that we have our Bore area numbers of .6 for a 7/8” master cylinder and .785” for a 1” master cylinder what do we do next? Carl states that a smaller master cylinder bore creates more pressure with an equal amount of force. A 1” master cylinder creates 127.4 PSI as compared to a 7/8” master cylinder which is 166.7 PSI based on your foot making 100 pounds of force at the master cylinder. It is important to consider that the smaller cylinder makes more pressure but the smaller bore will move less fluid. More travel will be needed to make up for the reduction in fluid moved by a 7/8” master cylinder as compared to the larger 1”. Carl explains further in the next section. Utilizing a bolt on caliper mount ensures that your calipers are square to the rotor improving pad wear and braking efficientcy. How do fluid volume and leverage come into play? Carl Bush: While a change in master cylinder bore size affects a pressure change, it also changes the amount of pedal travel realized to add the additional stroke needed to displace enough fluid to move the caliper pistons. This volume ratio plays an important role in the clamping capability of the caliper, and leverage that the driver has to generate that clamping force. The ratio between the caliper and master cylinder is a function of the net effective caliper piston bore area divided by the bore area of the master cylinder. To compare these ratios and do the calculation, you must start with the total piston area of the pistons in one side of one caliper. A front brake set using four piston calipers with 1.75” diameters will have a net bore area of 4.8” inches squared as each 1.75” diameter piston has an individual bore area of 2.4” inches squared. (Jeff’s Easy Math works for caliper piston bores too – 1.75” X 1.75” = 3.06” X Reusable Number .785” = 2.40” X 2 Pistons = Carl’s Net Bore Area of 4.8” Carl Bush-continued: By running the formula, the leverage ratio between a 7/8” bore master cylinder and the 1.75” four piston caliper will be equal to: Effective Caliper Piston Area (4.8) / Master Cylinder Bore Area (7/8 which is .6) = 4.8 / .6 = 8 for an 8:1 ratio. The driver leverage is then determined by multiplying the Pedal Ratio x the Caliper Piston Bore to Master Cylinder ratio. (Note from Jeff: “The pedal ratio is marked on your pedal assembly when you buy it or use the Pedal Ratio Drawing shown”. Carl’s Example: Pedal Ratio (6:1) x (Piston Bore (4.8) / Master Cylinder Ratio (.6) results in (8) = Driver Leverage (48:1) 6 x (4.8 / .6) = 48:1 You can substitute any number of piston bore combinations with master cylinder sizes with any pedal ratio to determine the driver’s actual brake leverage. For fun Carl has given you the answer to the test with this chart. Common Caliper Piston Size Diameter / Area Diameter, Inches 1.12 1.25 1.38 1.62 1.75 1.88 2.00 2.38 2.75 2.94 Area / Piston, Inches Sq .99 1.23 1.48 2.07 2.40 2.76 3.14 4.45 5.94 6.78 Common Master Cylinder Bore Sizes / Area Diameter, Inches .62 .75 .81 .88 1.00 1.12 Area / Piston, Inches Sq .31 .44 .52 .60 .79 .99 By changing to a 7:1 ratio pedal (from the 6:1 shown in Carl’s Example), the driver would then realize a final ratio of 56:1 with the same caliper and master cylinder (Jeff’s math 7 x (4.8 / .6) = 56:1). Consequently, a 5:1 pedal would only give the driver a 30:1 ratio (Jeff’s math 5 x (4.8 / .6) = 30:1). If we compare the front leverage ratio to the rear leverage ratio on any given car, this tells us the front to rear static bias capability of the car. Pedal Ratio is determined by dividing length "A" by lenght "B". The amount of force at "F" determines the force to the master cylinders. Now that we know the math, can you explain a common set up for our readers? Carl Bush: A common set up that could be found on a weekly show short track asphalt car is to use the example above with 1.75” piston calipers on the front with a 7/8” bore master cylinder, and a pair of 1.38” piston calipers on the rear with a 1” master cylinder. A 6:1 floor mount pedal ratio is also common. We have already determined that the 1.75 pistons with a 7/8” master cylinder and a 6:1 pedal will give the driver an overall brake leverage of 48:1 on the front. If we use the same formulas with the 1 3/8” piston calipers and 1” master cylinder on the rear, that produces a total driver’s rear leverage ratio of 22.75:1. When we compare the 48:1 ratio in the front, to the 22.75:1 ratio in the rear, we see that the car will be baselined with a front to rear static leverage bias of 67.8%, as long as the balance bar is centered and equal force is being applied to both master cylinders. You can substitute any combination of parts and their sizes to determine the exact influence they will have on the baseline static bias ratio. Four piston calipers can usually be found with piston sizes from 1.125" to 1.875". The area of two pistons on one side of the caliper determine the calipers influence on clamping capability. How do we use pressure to determine brake bias? Carl Bush: Although racing with a perfectly centered balance bar is the ideal goal, it seldom happens in reality. Besides, one of the advantages in using an adjustable balance bar is having the ability to adjust that leverage to optimize handling and driver comfort on track. Trying to measure the post-race leverage split at the balance bar is difficult and unrealistic. However, using pressure gauges to measure pressure differentials s at any given balance bar setting is relatively simple. The brake gauges will show the actual pressure split in the car based on the balance bar adjustments made by the driver. Those pressures can then be multiplied by the effective caliper piston bore areas to calculate the last on-track static bias settings. Calipers such as this metric replacement only have one piston on one side. The calculation of their clamping capability still uses the same formula. Going back to our (common set up) example, if we apply 50 pounds of leg force against a 6:1 pedal, we will generate 300 total pounds of force against the balance bar. If the balance bar is perfectly centered, it will distribute that force equally to each master cylinder. With each master cylinder receiving an equal force amount of 150 pounds, the 7/8” master cylinder should produce 250 PSI (Jeff’s math: 250 PSI comes from 150 divided by .6 which is the 7/8” master cylinder math result) while the rear 1” master cylinder produces 192 PSI (Jeff’s math: 192 PSI comes from 150 divided by .785 which is the 1” master cylinder math result). In practical use of gauges, you can use any level of effort and pressure for your comparisons. The end result will be the same. When the front pressure of 250 PSI from the 7/8” master cylinder is multiplied by the 4.8” inches of caliper bore area of the front 1.75” piston front calipers, we get a front clamping force of 1200. On the rear, we will have 192 PSI x 2.97” caliper area or 570 pounds of rear caliper clamping force. When comparing the these front to rear clamping force total in the same way you would compare wheel weights for balance, we would see that this car has a total of 1770 pounds of caliper clamping force at these line pressures with 1200 pounds or 67.8 % on the front. It’s that same static bias ratio that was measured using the overall driver leverage ratios. Now, if every car and driver had the same braking requirements and pedal feel preferences, we would never need to adjust anything. But, every car and every driver are unique and adjustments will get made. The ratio examples that have been used here are very common in many short track asphalt cars. But your car, for a wide variety of reasons, may have quite different requirements. As a racer or crew chief, you can use these formulas to map the existing brake set up on your own race car, and then make calculated decisions when the desired handling or driver feel isn’t being delivered. The inability to reach the desired bias or driver’s feel of the pedal is the indication you will need to evaluate your component selection and consider possible alternatives. By using the formulas in these examples, you can accurately calculate what affects a component change will make to your existing baseline, and record those final ratios in your records to use for future adjustments and set up for any given track type or conditions. Jeff Butcher As you can see, using the experience of you brake manufacturer is very valuable. Still, when you breakdown the math it is not all that hard. By understanding the pressures, bore areas and ratios you can improve your understanding of the brake system. A thorough understanding will help you to make improvements to an existing car or transfer learned knowledge to a new car. Be taking the time to understand the basic math behind the braking system you can calculate and record winning brake set ups. Slowing down to do the math will help you to go fast. Go forward – Move Ahead. Jeff Butcher JOES Racing Products 3/1/11
So if what I read is accurate, adding bigger wheel cylinders from 1 1/4" to 1 3/8" could help too...right?
It will increase the pressure of the lining against the drum but it will require more fluid volume from the master cylinder.
You guys make my head hurt. Hahahahaha!! I used this fruit jar one on my A bone... with a Wilwood residual valve... mounted on the frame. http://www.summitracing.com/parts/DHB-M32900 It has a 1" bore... and works great. I have Lincoln "self energizing" brakes all the way around... and the car is a Model A coupe. I ran the wheel cylinders that came with the Lincoln brakes up front... and then went with a smaller wheel cylinder (bore size) out back. My rationale for this is that with the fruit jar, you get equal amounts of fluid pumping in all directions... and while the rears won't have as much force applied to them as the fronts, they will actuate sooner than the fronts and pull the car straight as the brakes are applied at first. I may be a nut with my theories and such, but they work great. Also... don't quote me... but I made the pedal arm out of an old model A pedal... and I think the ratio is 7:1... I think. Sam
The Jalopy Journal
