Article And Photos By: Daniel Donley www.pandemoniumcustomchoppers.com
Originally Published In The March 2018 Issue Of Cycle Source Magazine
I have shown you in past articles how to rebuild calipers and master cylinders. This month I am going to go over some common issues with brake systems, because you will eventually come across these issues; it is just a matter of when.
Bleeding The Brakes:
So, you are trying to bleed your brakes and for some reason it is just not working and you’re ready to pull your hair out. Well, before you do that, here is a list of some common issues you may have when trying to bleed the brakes to help narrow down the problem.
Bleeder screw passages are corroded and plugged.
Replace or clean bleeder screw, also add a bleeder cap
Rubber brake lines over time can collapse inside and get plugged; inhibiting the flow of brake fluid. I like to install new brake lines on any new project.
I have seen master cylinders, new and old, leak. A quick inspection of pulling back the rubber boot to inspect for brake fluid, this is a sign of internal seals leaking. The master cylinder will needs rebuilt or replaced. Master cylinders can also leak internally. A master cylinder internal piston has 2 seals on it, one could leak to the other. How I check for this is to pump the brake quite a few times. Wait a second, then pump one time very quickly, while looking for a bubble to come up through the fluid. This is a sign of internal leaking and the master cylinder will need to be rebuilt or replaced. Your brake caliper piston could be stuck, not allowing fluid into the caliper. The brake caliper piston seals could be leaking and letting air into the caliper. The brake pedal pushrod could be adjusted incorrectly not allowing for a full stroke in or out. Adjust pushrod for a minimum of a 1 /16” of free play. This will allow for full stroke in and out.
When building custom motorcycles, we like to orientate the brake calipers in many locations around the rotor. When the caliper is mounted in the downward position say 6 O’clock the bleeder screw is also at the lowest point. This will allow the caliper to
hold air. The caliper must be removed from its bracket and the bleeder screw pointed up. Before you’re able to remove the air from the caliper while bleeding.
Brake systems typically use DOT 3, 4 or 5 brake fluid. You CANNOT MIX 3 or 4 with 5!!! IT WILL Turn to GEL!! How do you know which one you have? You cannot always go by what the cover says is required, over time it may have been changed. DOT 3 & 4 have a very bitter taste, DOT 5 has NO taste. I cannot tell the difference
in the color of them when they are old. New DOT 5 is typically purple or green. Use the fluid the cover says. DOT 3 & 4 fluids have a swelling agent in them to allow the seals to swell and seal. DOT 5 does NOT have the swelling agents in them. So, if you put DOT 5 in a DOT 3 or 4 system and it works but it is leaking now you know why. Air in your system is the most common reason you cannot bleed your brakes. Sometimes you have to get creative and bleed the system at every joint. To remove the air completely. Spongy brakes are also very common. This is when the pedal or lever feels mushy and you don’t feel the resistance in the lever or pedal that you should.
Brakes And Custom Bikes
I see this one a lot. When people build their own foot controls. The lever ratio at which your foot presses on them to the ratio of the amount of force being exerted on the master cylinder is incorrect. Think of it
as a teeter totter. I like to keep the pedal length comfortable on my foot and the push point to the master cylinder as close to the pivot point as possible. This is called the brake pedal ratio. This can get very complicated. Please do your research on this one to come up with a ratio that is suitable for you and your project
I see a lot of people using sport bike master cylinders on their custom builds. These master cylinders were typically designed to run two 4 piston calipers. When you install this on a one brake caliper application you will have spongy brakes. Why? The piston bore size in the hand brake is too large for a 1 caliper application. You will want to make sure that the master cylinder bore size is correct for your brake caliper application. You don’t want to use rubber brake line for high performance braking systems. They can flex and swell leaving you with the spongy feeling. I like to change my brake fluid every 2 years. This will provide you with proper braking performance. The calipers on early to mid-2000 Harley-Davidson’s are also known for sponginess after time. The reason this happens is the brake piston seals become dry and do not let the brake caliper pistons react as they should. A quick way to resolve this problem is to remove the caliper and clean around the pistons with some brake cleaner then with a Q-tip spread some light weight oil onto the pistons. You will want to work the pistons in and out a few times to get lubrication into the seals. This great tip was shown to me by a NASCAR Mechanic.
Don’t Be A Drag:
A dragging brake is also another common thing that I see, this can
not only be dangerous but can ruin brake pads and rotors very quickly. When building your custom motorcycle, you want the calipers centered over the rotor. Typically, most people can accomplish this. But what happens is when you send the brake caliper bracket out to get chrome plated or powder coated these coatings add a measurable thickness to the bracket and throw it off center of the rotor. Make sure that you take your coating thickness into consideration when building your sweet ride. I have seen with the use of older brake lines sometimes they can collapse internally. So, when you apply pressure to the lever or pedal they will actuate the brake because it’s under pressure. Then when you release the pedal or lever the line will collapse and retain some pressure on the brake making it drag. There is no real way to know this for sure other than replacing the old brake line with new. Brake lever or pedal free play can be adjusted incorrectly. This is where the pedal or lever is continually pushing on the master cylinder piston and not releasing completely retaining some pressure on the brake caliper causing drag. Brake pedal free play should be at least 1/16 of an inch before it makes contact with the master cylinder piston. This will allow for expanding and contracting of the fluid and parts.
Older calipers or ones that have been sitting for quite some time typically have had brake fluid left in them and over time it starts to corrode the caliper body and piston. This will cause the piston to stick or not react correctly. You will need to disassemble and clean these components and inspect for damage.
Allowing your brake to drag continually over time will eventually warp your rotors. You will know that this has happened when you apply the brakes and feedback through the pedal has a pulsating action. Beware of buying or using used rotors they are not being used for a reason. This may be one of them.
Recently reassembling a bike with my friend Hugh, we were bleeding the brakes using my “Mighty Vac”, we were struggling to get the rear brake bled, eventually we did. But the rear wheel was dragging severely, we checked all the above things listed in this tech article, everything checked out just fine. The problem ended up being the 90’s style Harley brake caliper. It is set up with sliders like on an old Chevy pickup. The pads move on the sliders and the problem was the new brake pads have a metal backing that is stamped on a machine this creates an angle on the edge of the pad. This angle was creating too much friction for the pads to slide properly. A quick trip to the belt sander to square up these areas fixed this issue. Go Figure!
Brake systems, in theory, are very simple, but yet can be SOOO complicated when problems arise. These are some of the scenarios that I have encountered working on bikes for many years. Hopefully my experiences will help get some of the learning curve out the way. I’m proud to say this marks my 7th year writing for Cycle Source and my 84th tech article. If there is something that you would like to see me do an article on give me a call or email me with your idea. If you have any questions, please feel free to call me at the shop anytime 419-576- 6812 Daniel Donley Pandemonium Custom Choppers email@example.com