I have just purchased a Road King Custom with a TLE side car and am making some adaptive modifications since I’m a paraplegic. A Pingel electric shifter and a Champion reverse gear kit are the easy modifications. Linking the brakes or converting to a two handed operation of the brakes is next. I mentioned this as a challenge in a previous post and a couple of people responded with suggestions to simply link the front and rear/sidecar brakes with a proportioning valve. My experience is that it is not as simple as that. Please excuse my lengthy post; my intent is to share how I came to that conclusion.
Example 1: My first attempt at getting back on a bike was with a Moto Guzzi V11 Sport. I designed and fabricated a primitive retractable training wheel system which I later abandoned as being unsafe for reasons unrelated to braking. However, I did experiment with linking the front and rear brakes with a proportioning valve. I simply added a brake line from the front master cylinder to the rear caliper with a Willwood proportioning valve and discovered the braking performance and feel was degraded with the valve in any position other than fully closed. Opening the valve enough to make the rear wheel stop resulted in mushy feel and the lever traveling almost to the hand grip.
Example 2: I had a GL1500 with a well developed and safe system of retractable training wheels. The Honda had a linked brake system from the factory. One of the front disk brakes was actuated by the right hand lever and the other front disk and the rear disk were linked and actuated by the foot pedal. Again experimenting, I converted the front brakes to conventional dual disk operation by the stock handle bar mounted master cylinder (with the rear brake isolated). This did not work. The front brakes again felt mushy and the bike took longer to stop in this configuration than it did with just the one front disk.
I also spent a fair amount of time converting a kart to hand controls and again learned there is a very complicated relationship between the bore and stroke of the master cylinders and calipers as well as the leverage effect of the actuating lever and force applied to that lever.
Getting my hands on a copy of “Brake Handbook” by Fred Puhn just confirmed that my math and engineering skills are not up to snuff. I did learn that adding volume to the slave cylinders (adding calipers) requires an appropriately smaller master cylinder. But, how much smaller?
So I’m looking for help from those that may have experienced success through trial and error. Or from those that have read the Brake Handbook and understand it!
My preference would be to operate all four brakes from the right hand lever. Second choice would be to operate the rear wheel and hack wheel brakes with a left hand thumb brake. Anybody have specific experience with what will work on a Harley rig?
I've been under the assumption that adding more volume to the system (adding calipers) will require a larger volume master cylinder to operate the system correctly. How does a smaller bore master cylinder efficiently operate more slave units without running out of fluid/pressure? The fluid in the reservoir only comes into play on the second squeeze. Too late in some scenarios.
The second handlebar control for the rear bike & sidecar discs seems the most efficient for the least cost. No proportioning valves needed.
One of my paraplegic sidecar customers has rigged a left side lever that uses a sports bicycle lever assembly to operate the rear brake unit. He has limited strength in his left hand and says this setup works fine for him. A similar fix would work on the Harley I imagine.
Lonnie
Lonnie,
Somebody much more informed than me would have to explain why a smaller master would be needed when adding calipers to the system. Like you I assumed the same thing and was surprised to learn other wise when reading about basic hydraulics in Puhn’s book. This much I understand (I think……): assuming you want to maintain the same force applied to the lever and the same force applied to the slave pistons, if you add piston area to the slave, then you have to decrease piston area of the master. If you don’t decrease the master piston area it will require greater force at the lever to achieve the same force applied to the slave. My head hurts…….
Was your paraplegic customer’s rig a Harley? If yes would you be so kind as to ask him to contact me? Thanks.
Kirk
kfeye@pacbell.net
Going to a smaller bore master will keep the effort about the same as you now have however unless you add a lot more stroke to the master your brakes will not work. To keep the same stroke and work more brakes you need a larger bore however your effort will go up. With hand controls it is difficult to add more stroke so you usualy end up needing to accept having to use more force to apply the brakes and thus go with a larger bore master.
Jay Giese
Dauntless Motors Corporation
866-638-1793
Sorry Kirk,
He has a Honda rig.
