Determining Pedal Ratio The key to a hydraulic clutch setup is getting the pedal ratio correct. In fact, it’s critical, and an inch or two can make all the difference in how the clutch performs. Just like a brake pedal, the clutch pedal acts as a lever to increase the force applied by the driver to the master cylinder. That force tells the master cylinder to send fluid to the release bearing or clutch slave. If you examine a clutch pedal, you’ll see the pivot point (where the pedal moves) and the mounting point/hole for the master cylinder pushrod are quite often different. By varying the length of the pedal and/or the distance between the pushrod mount and the pedal pivot, you can change how much force (via your left leg) is required to energize the master cylinder. This is the mechanical advantage, or pedal ratio. What you need to do is to figure out a ratio that provides enough force to energize the master cylinder without requiring too much effort on your leg’s part. Let’s start at the beginning. The typical adult male leg can exert roughly 300 pounds of force. If you’ve ever tried to single-leg press 300 pounds at a gym, you know that’s a bunch. When you’re figuring out the right pedal ratio for the clutch, shoot for a force number that is 1/3 or less than that 300 pound figure. That will make working the clutch much more comfortable. Next, you have to translate that 100 or so pounds of leg force into approximately 600 psi. You can do this by changing the overall length of the pedal, but it’s usually easier (and far more practical) to shorten the distance between the pivot point and the master cylinder pushrod mount location by drilling a hole for a new pushrod location. If you go overboard in the pedal ratio department, the clutch can become over-sensitive or touchy. So how do you get it right? First, you need some measurements: Height of the pedal from the very bottom through the centerline of the pivot point Center-to-center measurement through the pivot point and the clutch pushrod hole in the pedal lever Using an aftermarket reproduction clutch pedal as the example, dimension #1 is 13.25 inches. There are two different stock pushrod holes available (measurement #2): three inches and 3.625 inches. To determine pedal ratio, divide figure #1 by #2. Here’s how the ratios look for our example: 13.25 / 3 = 4.41 ratio 13.25 / 3.625 = 3.63 ratio The recommended pedal ratio with either a 7/8- or 3/4-inch bore clutch master cylinder is around 6:1, so we would need to drill a new pushrod hole approximately 2.2 inches from the pivot point to get the optimum pedal ratio (13.25 / 2.2 = 6.072). Take a look at the photos and captions above to see how simple a hydraulic clutch system really is. In a few weeks, we’ll look at some mechanical linkage options.
Read more at OnAllCylinders:
Please Release Me: How to Set Up a Hydraulic Clutch: http://www.onallcylinders.com/2013/07/05/please-release-me-how-to-set-up-a-hydraulic-clutch/?utm_source=oac-link&utm_medium=link&utm_campaign=copypaste
Determining Pedal Ratio The key to a hydraulic clutch setup is getting the pedal ratio correct. In fact, it’s critical, and an inch or two can make all the difference in how the clutch performs. Just like a brake pedal, the clutch pedal acts as a lever to increase the force applied by the driver to the master cylinder. That force tells the master cylinder to send fluid to the release bearing or clutch slave. If you examine a clutch pedal, you’ll see the pivot point (where the pedal moves) and the mounting point/hole for the master cylinder pushrod are quite often different. By varying the length of the pedal and/or the distance between the pushrod mount and the pedal pivot, you can change how much force (via your left leg) is required to energize the master cylinder. This is the mechanical advantage, or pedal ratio. What you need to do is to figure out a ratio that provides enough force to energize the master cylinder without requiring too much effort on your leg’s part. Let’s start at the beginning. The typical adult male leg can exert roughly 300 pounds of force. If you’ve ever tried to single-leg press 300 pounds at a gym, you know that’s a bunch. When you’re figuring out the right pedal ratio for the clutch, shoot for a force number that is 1/3 or less than that 300 pound figure. That will make working the clutch much more comfortable. Next, you have to translate that 100 or so pounds of leg force into approximately 600 psi. You can do this by changing the overall length of the pedal, but it’s usually easier (and far more practical) to shorten the distance between the pivot point and the master cylinder pushrod mount location by drilling a hole for a new pushrod location. If you go overboard in the pedal ratio department, the clutch can become over-sensitive or touchy. So how do you get it right? First, you need some measurements: Height of the pedal from the very bottom through the centerline of the pivot point Center-to-center measurement through the pivot point and the clutch pushrod hole in the pedal lever Using an aftermarket reproduction clutch pedal as the example, dimension #1 is 13.25 inches. There are two different stock pushrod holes available (measurement #2): three inches and 3.625 inches. To determine pedal ratio, divide figure #1 by #2. Here’s how the ratios look for our example: 13.25 / 3 = 4.41 ratio 13.25 / 3.625 = 3.63 ratio The recommended pedal ratio with either a 7/8- or 3/4-inch bore clutch master cylinder is around 6:1, so we would need to drill a new pushrod hole approximately 2.2 inches from the pivot point to get the optimum pedal ratio (13.25 / 2.2 = 6.072). Take a look at the photos and captions above to see how simple a hydraulic clutch system really is. In a few weeks, we’ll look at some mechanical linkage options.
Read more at OnAllCylinders:
Please Release Me: How to Set Up a Hydraulic Clutch: http://www.onallcylinders.com/2013/07/05/please-release-me-how-to-set-up-a-hydraulic-clutch/?utm_source=oac-link&utm_medium=link&utm_campaign=copypaste
the rod i stole from you ;)
