If your motorcycle brake caliper won’t release, your bike won’t move. Or if it does, you’ll feel the resistance when you let off the throttle.
It can be frustrating to be having problems with your motorcycle brake calipers.
Here is a list of reasons your motorcycle brake caliper won’t release, and how to diagnose or fix the problem.
Table of Contents
1. Clogged Up Ports in the Master Cylinder Reservoir
When you squeeze your hand brake or put pressure on the foot brake, you are pressurizing the hydraulic fluid in the brake line. This pressure pushes down the pistons on your caliper to squeeze the brake pad into the brake disc.
The master cylinder is an essential part of your braking system. Brakes use a pressure-activated hydraulic system. Right underneath the brake fluid reservoir is the master cylinder.
When you pull in your hand lever, or put pressure on your rear brake’s foot lever, the master cylinder piston pushes the brake fluid into the brake line.
This pressurizes the brake fluid in the hydraulic line and causes the pistons on the caliper to press the brake pads up against your braking disk or wheel cylinder, in the case of drum brakes.
When you release the brake lever or pedal, the fluid returns to the master cylinder reservoir. If there is any stoppage or clogging in the holes between the reservoir and the master cylinder, you may be pressurizing the brake line without being able to relieve the fluid pressure.
In this case, you won’t be able to release the brake caliper on your motorcycle’s wheels.
The best plan of action is to carefully remove the master cylinder from the brake line and clean it.
There are two fluid ports leading into and out of the master cylinder. The fluid inlet port allows fluid to pass into the system when you squeeze the brakes, and the compensating port allows the fluid to return to the reservoir when you relieve the pressure.
Take care to clean out the ports, focusing on the compensating port where the fluid should be returning to relieve pressure in the brake line. If there is any debris, dirt, or gunk clogging up the port, clean it out with brake cleaner.
If this is the case, you will also need to bleed new brake fluid into the lines until all old fluid, any debris, and all air are out of the brake line.
2. Stuck Or Broken Return Spring in the Master Cylinder
The return spring is a component inside the master cylinder. When the brake lever or pedal is released, the return spring pushes the master cylinder piston back into place, relieving the pressure in the hydraulic system.
If your return spring has broken or is sticking in the depressed position, it won’t push the master cylinder piston back into the passive position and won’t release the brake caliper.
If this is the case, you will need to replace the spring, or more probably, the entire master cylinder.
Try to open the spring and piston chamber on the master cylinder and replace the spring. If you cannot replace the spring, you will need to remove the faulty master cylinder and replace it with a new one.
3. Too Much Brake Fluid In the Caliper
Brake fluid expands as it gets hot. That’s why there are different brake fluids, DOT 3, 4, 5, and 5.1. These different brake fluids have different boiling temperatures. DOT 3 brake fluid is the lowest boiling point and 5.1 is the highest.
Because brake systems are hydraulic, they work on a pressure system. Too much brake fluid in the caliper will expand when heated and cause your brake caliper to stick in place, with the brake pads firmly applied to the disk.
Brake caliper seizure is a common reason your motorcycle brake caliper won’t release. Fortunately, there are some simple things you can do to relieve the pressure and free the brake caliper.
Much like the problem with clogged ports in the master cylinder (which can be the culprit for this specific problem), you have too much pressure in the hydraulic brake line.
Cracking the bleeder valve can immediately relieve the pressure. To do this, find your bleeder valve-it should be right next to the brake line seal, where the fluid enters the caliper.
There will be a rubber nipple over the valve that needs to be removed. Use the appropriate size of wrench to open the bleeder valve.
The bleeder valve will release fluid with just a ¼-½ turn. Be sure not to open the bleeder valve too hard. You don’t want to release all the brake fluid, as it is corrosive and messy.
If you are just relieving the pressure from too much fluid in the caliper, hold a rag or cloth tightly under the bleeder valve to catch any fluid that is released.
Another way to relieve the pressure from the brake caliper is to put a flathead screwdriver in between the pads and push the pads away from the disk.
This reverse bleeding technique can push the pressure back up the line, but you will need to further diagnose the real reason your brake fluid is gathering in excess in the caliper.
4. Old Brake Fluid
Brake fluid will deteriorate over time and that’s why it is suggested to replace it every two years. During the life of your motorcycle’s brake fluid, water will slowly accumulate in the fluid.
While new brake fluid is a clear yellow, old brake fluid will be darker because of minor rust collection within the brake line.
Either open your brake fluid reservoir on the bike’s handlebar or crack open the bleeder valve to look at the quality of the fluid. If it is old, you will need to replace it by bleeding your brakes.
Because brakes are such an integral safety feature on your bike, it may be intimidating to work on the brake system, but don’t be discouraged. It’s fairly simple to bleed your brakes with only a few steps!
Here’s how to bleed the old brake fluid out of your lines and replace it with new fluid:
- Open the brake fluid reservoir on your handlebars. Using a Phillips head screwdriver, remove the two screws that hold the lid on the reservoir. Make sure to cover the gas tank with shop cloths or rags-brake fluid is corrosive and can damage your paint job.
- Remove the rubber cover from the brake bleeder valve. Your brake bleeder valve is located on the brake caliper.
- Attach a small piece of vinyl bleed tubing to the head of the bleeder valve. Place the other end of the tubing in a plastic or glass container to catch the brake fluid that is bled out.
- Pump your brake three times. This builds up the pressure line you will need to push the brake fluid through your brake line and out of the bleeder valve.
- Crack the bleeder. A ¼-½ turn will be more than enough to open the valve. You want a slow, steady amount of brake fluid to release from the bleeder valve. After the small amount of fluid is pushed out, close the valve again.
- Repeat steps 4 & 5 until clean, yellow fluid is flowing through the bleeder valve. It can take some time and repetition to bleed your brake fluid, so be patient.
- After you are finished with the front brake, move to the back brake. Even if only one caliper won’t release, they share the same fluid and if it is degraded, it can cause the same problem.
5. Stuck Pistons
The brake caliper uses a system of pistons to apply the brake pads to the disk. The hydraulic pressure from the brake line moves the pistons out of the caliper housing, pressing the pads into the disk to cause the friction you need to stop the motorcycle.
Heat, calcified build-up, and sticking parts can cause the motorcycle brake caliper to seize up.
In the case of a seized-up brake caliper, you will need to remove the caliper, clean and grease all moving parts, replace smash rings and rubber seals, and replace.
This is a meticulous process and if you aren’t comfortable mechanically, we suggest you leave this to a professional motorcycle mechanic.
The Importance of Brake Systems
Seized-up calipers can happen suddenly and throw you from your bike, so make sure to give your brake system the once-over when you do a pre-ride visual inspection.
If your brake caliper isn’t fully released, the friction between the pads and brake discs can cause substantial heat, warping the disc and causing further braking problems.
Alongside safety gear like helmets, riding leathers, and tough boots, your brake system is the most used piece of safety gear you have.
If you do a lot of hard braking for any reason, you should do regular maintenance on your braking system more often. Experts recommend heavy brake use should spur you to bleed your brakes every 6 months.
Brake systems in general should be maintained meticulously to avoid any emergency situations that might arise from faulty brake operation.