Combining brakes to hand brake lever

Information and questions on GL1500 Goldwings (1988-2000)
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Motorcycle: 1995 GL1500A Aspencade Trike with Motor Trike kit

Combining brakes to hand brake lever

Post by Shootdaroc » Tue Oct 13, 2015 9:36 am

I have a 1995 GL1500 Aspencade with a Motortrike trike kit. As a disabled rider I am trying to combine most (if not all) of the brakes to the hand lever. Originally the hand lever only worked the right front disc brake. Last winter I had my mechanic route a new brake line to work the two drum brakes on the trike. He felt the hand lever master cylinder would support either the two front disc brakes or the two drum brakes in the back. I didn't think I would want both fronts only in an emergency situation, so opted to have the two rear drum brakes. I now find that the stopping power of only the rear drum brakes is not adequate. Not even as good as the original right front disc, so I need to add at least one front disc brake to the equation...

Has anyone accomplished this brake setup?
Is the Front master cylinder from a GL1800 bigger than the GL1500?
Could a right side delay proportioning valve off a GL1800 be used?
Any help would be most appreciated... Ron

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Re: Combining brakes to hand brake lever

Post by WingAdmin » Tue Oct 13, 2015 9:59 am

The problem you're going to have is just how much effort it takes to brake.

The hydraulic brake system is essentially a force multiplier. You squeeze the lever which moves a small piston a relatively large distance through its bore, pushing fluid down the brake lines.

This fluid then exerts pressure against two large pistons, which move a relatively tiny distance. Let's say you squeeze your lever with 10 pounds of force, and in doing so the lever moves 2 inches.

The piston in your master cylinder moves much less, because of the lever action of the brake lever. Let's say the piston moves 0.5 inches. 2 inches divided by 0.5 inches = a force multiplier of 4, which means the piston translates your 10 pounds of force into 40 pounds of force being exerted on the piston.

The piston travels 0.5 inches, and pushes fluid down to a brake caliper. There are two pistons in the brake caliper. The total area of the pistons (based on their diameter) is 1.5 square inches. The total area of the piston in the master cylinder is 0.05 square inches. 1.5 divided by 0.05 is 30, so multiply our 40 pounds of force by 30, and we get a total of 120 pounds of force being applied to the brake pads, simply by squeezing your brake lever with 10 pounds of force.

Of course, because the caliper pistons are that much larger, they move much less. With the master cylinder piston moving 0.5 inches, we divide that by the difference in area between master and slave pistons (40), which tells us that the pistons in the brake caliper move only 0.0125 inches. Fortunately, this is all that we need, because the pads rest almost right on the brake rotors - and moving only this tiny amount is enough to have them contact the rotor.

Now we add another brake caliper, which effectively doubles the area. We need twice as much fluid moving through the brake lines in order to move the second set of pistons the same amount. We can't double the lever travel from 2 inches to 4 inches, because our hands aren't that big! So instead we have to increase the size of the piston in the master cylinder - let's say we double it. Now in order to actuate the caliper pistons the same amount, and apply the same amount of force, we have to apply twice the force to the lever - 20 pounds instead of 10.

Now add two more - for two front calipers and two rear calipers - and we are well beyond what can be reasonably applied using your hand. This is what brought about the advent of "power brakes" in cars - essentially using vacuum from the engine to boost the brakes, reducing effort required from the driver.

So what is the answer? The GL1800 type system might be an option, if it could be adapted. It adds a second master cylinder built into a brake caliper, and the brake caliper is allowed to pivot. When the rider applies brakes, the caliper "grabs" the brake rotor. Because it can pivot, the brake rotor pulls the caliper slightly, which then pushes the secondary master cylinder piston into its bore, and this is what then actuates the other brakes. Basically you're using the bike's momentum as a brake booster to actuate the second brakes.

How this would be done, or if it could be done is a little out the scope of this discussion - you're talking a fair bit of custom fabrication and adaptation.

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Re: Combining brakes to hand brake lever

Post by Mh434 » Tue Oct 13, 2015 2:11 pm

Although I haven't researched them there are small power brake boosters for ATV's available. Maybe that would be an option...

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Re: Combining brakes to hand brake lever

Post by Shootdaroc » Tue Oct 13, 2015 3:39 pm

Let me first thank you (wingadmin) for the very quick and detailed reply. Not being a hydraulics major I thought the issue was volume, not pressure! Your explanation really puts a different twist on this modification.

It has also been suggested that we use a slave cylinder to actuate the rear master cylinder since it is already setup for the 2 rear and the left front brakes. I figured that it would be much easier to run connecting lines and maybe proportioning valves, but it sounds like it won't be that simple.

Lastly, I want to thank you for providing this forum. I have learned sooooo much from it about my bike and would never have gotten the Pingle electric shifter to work properly if I had not found out about the shifter brace. The how-to article on installing the brace was spot on and the photos were outstanding (as are all the how-to articles)!

As I was writing this I saw the suggestion on the power booster. Another good idea to look into. Thanks everyone for your suggestions. Somehow, I know it will work!!

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