ntsqd
heratic car camper
I've posted a lot over the years on this topic. I've an older thread on the IH8Mud forum covering the whole topic of brakes. I'm far from a real expert, but I did spend two years working in the industry at wilwood and several decades since working with and observing other's brake system results. There is at least one person here whom I know easily exceeds my applied knowledge on the topic.
In this thread: https://classicbroncos.com/forums/t...n-manual-disc-disc-brake-combinations.324668/ I mentioned that my mentor while at wilwood developed a simple formula to set-up a manual disc brake system. It should be noted that this formula does not consider the rear brakes. That said, I spent the next 10+ years watching how well the formula agreed with the system configurations that people arrived at, whether they used the formula or got there by some other means. The formula has proven to be a reliable predictor of how the system will feel to the operator.
The formula itself is simple. The combined hydraulic and mechanical leverage is ideal at 95:1. Seems simple enough? What's important are the boundaries, and this is where I've had to expand beyond what my mentor originally proposed. As most know, brake pedal feel is very subjective. Most can agree on a narrow range of pedal feel being OK, but what it ideal to one person isn't even close for another. These boundaries have been established by watching the topic for literally decades and aligning the results with the formula. In the direction of a hard pedal that still stops the vehicle about 93:1 is as low as most are willing to go. In the other direction there seems to be a bit more tolerance. Can get out to 100:1 before most all will complain about the pedal feeling mushy.
How to figure out your total ratio requires knowing the pedal's mechanical ratio, the bore size of the caliper piston(s), and the bore size of the master cylinder. Total Ratio is the ratio of the hydraulic piston areas multiplied by the pedal ratio. For hydraulic ratio that means the areas of both front calipers are added together, then divided by the m/c piston area.
I'll start with the standard Ford sliding caliper. It has a 2-7/8" piston OD. I've no idea what the actual ratio of an EB's brake pedal is, but it is in my notes that it is 6:1 so I'm using that. With that pedal ratio a Ø1-1/32" m/c will have a Total Ratio of 93.3:1 That's a little low on the ratio. The pedal will be rock solid, but the truck isn't going to stop very easily.
If a Ø1.00" m/c is put in the system then the Total Ratio is 99.2:1 and it takes 157 lbf on the pedal to generate 1200 psi in the system. That's a bit high in ratio. More than a few will think that the pedal is too mushy.
Let's say that the T-Bird calipers are used to replace the std. Ford calipers. Those have a Ø3-3/32" piston in them. Still using the 6:1 pedal ratio combined with an Ø1-1/8" m/c the Total Ratio is 94:1. That's closer to the theoretical ideal of 95:1 and I suspect that most would be happy with that pedal feel.
Hopefully this shows how this is simple, yet difficult at the same time. The calcs are easy, but finding the right combo of parts is not. Setting up a spreadsheet to examine all of the combinations is really helpful.
In this thread: https://classicbroncos.com/forums/t...n-manual-disc-disc-brake-combinations.324668/ I mentioned that my mentor while at wilwood developed a simple formula to set-up a manual disc brake system. It should be noted that this formula does not consider the rear brakes. That said, I spent the next 10+ years watching how well the formula agreed with the system configurations that people arrived at, whether they used the formula or got there by some other means. The formula has proven to be a reliable predictor of how the system will feel to the operator.
The formula itself is simple. The combined hydraulic and mechanical leverage is ideal at 95:1. Seems simple enough? What's important are the boundaries, and this is where I've had to expand beyond what my mentor originally proposed. As most know, brake pedal feel is very subjective. Most can agree on a narrow range of pedal feel being OK, but what it ideal to one person isn't even close for another. These boundaries have been established by watching the topic for literally decades and aligning the results with the formula. In the direction of a hard pedal that still stops the vehicle about 93:1 is as low as most are willing to go. In the other direction there seems to be a bit more tolerance. Can get out to 100:1 before most all will complain about the pedal feeling mushy.
How to figure out your total ratio requires knowing the pedal's mechanical ratio, the bore size of the caliper piston(s), and the bore size of the master cylinder. Total Ratio is the ratio of the hydraulic piston areas multiplied by the pedal ratio. For hydraulic ratio that means the areas of both front calipers are added together, then divided by the m/c piston area.
I'll start with the standard Ford sliding caliper. It has a 2-7/8" piston OD. I've no idea what the actual ratio of an EB's brake pedal is, but it is in my notes that it is 6:1 so I'm using that. With that pedal ratio a Ø1-1/32" m/c will have a Total Ratio of 93.3:1 That's a little low on the ratio. The pedal will be rock solid, but the truck isn't going to stop very easily.
If a Ø1.00" m/c is put in the system then the Total Ratio is 99.2:1 and it takes 157 lbf on the pedal to generate 1200 psi in the system. That's a bit high in ratio. More than a few will think that the pedal is too mushy.
Let's say that the T-Bird calipers are used to replace the std. Ford calipers. Those have a Ø3-3/32" piston in them. Still using the 6:1 pedal ratio combined with an Ø1-1/8" m/c the Total Ratio is 94:1. That's closer to the theoretical ideal of 95:1 and I suspect that most would be happy with that pedal feel.
Hopefully this shows how this is simple, yet difficult at the same time. The calcs are easy, but finding the right combo of parts is not. Setting up a spreadsheet to examine all of the combinations is really helpful.
