A bent brake rotor on your dirt bike can quickly ruin your ride day. This commonly happens with a direct impact to the rotor or rotor disc brake guard. Mud, sticks, rocks and other debris can also cause the disc rotor to bend or break beyond repair. You can protect both rear and front brake discs with disc brake guards. They effectively protect the disc from direct impact bends and debris.
Straightening a bent brake rotor on a dirt bike includes placing the dirt bike on a center stand. Next, while rotating the front wheel, use a marker to mark the bent area into the brake rotor. Finally take an adjustable wrench and slowly bend the rotor, until the rotor is true.
Luckily, most slightly bent disc brake rotors can be straightened. In this guide, we are going to help you figure out if the rotor can be fixed and show you how to straighten or true a bent brake rotor on a dirt bike or a mountain bike.
In this article, you will find:
- How to diagnose a bent brake rotor?
- 3 Steps to straighten or true a bent brake rotor disc
- Tools needed to fix a bent brake rotor on a dirt bike
- Step 1: Inspect the bent rotor disc and wheel
- Step 2: Find the warped area of the disc with a marker
- Step 3: Straighten the disc with a wrench
- and much more!
How To Diagnose A Bent Brake Rotor?
A bent brake rotor is usually fairly simple to diagnose. The most common symptom is a pulsation feeling in the front brake level or on the rear brake pedal. When you apply brake, the lever or the pedal feels like it’s moving or pulsating, and the frequency is speed related. The warped disc will also push the brake pads apart and cause a longer brake lever/pedal actuation. This often requires pumping the brake to push the pads closer to obtain desired braking force.
In summary, typical symptoms are:
- Pulsating brake lever or brake pedal when applying brake
- Poor brake performance
- Brake lever or pedal movement increases when first applied during riding
- Dragging or grinding sounds coming near front or rear disc when moving or riding the dirt bike
- Uneven brake pad wear
- Visually bent rotor
All these above mentioned symptoms mean that you should stop riding and perform an inspection on the brake system. Typically the warped or bent brake discs are easy to diagnose and test.
How Do You Fix a Bent Disc Brake?
A bent dirt bike disk brake is fixed by using an adjustable wrench to bend the rotor back to true. You can also use a disc truing tool.
Can You Straighten a Dirt Bike Rotor?
This is a common question, as we can see here in popular forums.
Yes, in most cases you can successfully straighten a dirt bike rotor. If the rotor is slightly bent and not cracked or otherwise damaged, it can be straightened using a rotor truing tool or an adjustable wrench.
No heat is needed as the disc brakes are thin and bend fairly easily without cracking.
In scenarios where the dirt bike rotor is bent by a sharp hit and the rotor grinds into the brake caliber, the straightening may not work.
Next, lets begin straightening the bend.
3 Steps To Straighten Or True A Bent Brake Rotor Disc
Now that we have identified a bent brake rotor, we can straighten or true the rotor. Most bends are small enough where they can be fixed.
If you are able to push the dirt bike back and forth and the rotor is not locking the wheel, you are in luck. Unless the rotor is otherwise damaged or broken off, bending it back to true is possible.
Tools Needed To Fix a Bent Rotor
Tools that you will need to fix a bent brake rotor are:
- Center stand or similar to lift the wheel off the ground
- An adjustable wrench or
- a disc truing tool to bend the disc with
- Marker or sharpie to find and mark the bent area of the disc
Step 1: Inspect The Bent Rotor Disc and Wheel
Let’s begin by placing the dirt bike on the center stand. Place the wheel that has the bent brake rotor off the ground, so you can freely rotate the wheel.
Typically the front wheel stays on the ground when you lift the dirt bike on the center stand. If you are working with the front rotor disc, use a tool, wrench or similar, about an half an inch thick item and place it under the front of the skid plate. This will lift the front wheel off the ground.
Next, rotate the wheel around and inspect the wheel bearing play for wear. Sometimes worn out wheel bearings can cause wheel wobble when braking that feels very similar to a bent brake rotor. You can quickly check the wheel bearing play by grabbing the wheel from top and bottom and wiggling the wheel and inspecting the wheel bearing and axle area for any visible play.
Most bent rotors can be seen wobbling when rotating the wheel. Spin the wheel and visually inspect the rotor for any wobbling, side to side movement or deviation.
Step 2: Find The Warped Area Of The Disc With A Marker
Place the sharpie or a marker next to the front fork or the rear swing arm near the rotor. You can use a clamp or tape or just hold the marker in place by hand. If working with the rear rotor, find a spot near the swing arm.
Next, spin the wheel and slowly push the marker closer to the bent brake rotor, so that the marker leaves a streak in the bent area of the brake rotor. If the bend is to the inside, you should use the same technique except mark the area that is not bent. This leaves the bent area without the markings.
You can also anchor the marker near the brake caliper and slowly rotate the wheel to find the area with the bend.
Step 3: Straighten The Disc With a Wrench
Using the adjustable wrench or the truing tool, slowly bend the brake rotor back to true. Go slowly and in small increments at a time.
For bigger and sharper bends, use a smaller wrench and place the tool to cover only the outer edge of the brake rotor disc. An inch is enough or equal to the brake pad width.
Alternatively you can use the wrench to bend the disc from the rotor arm. These methods move the disc faster by applying the force directly to the bent area. Use two wrenches, like in the picture above, to bend the rotor arm. Lifting the wrench will push the rotor bend inwards and vice versa.
For smaller bends or warping, position the tool deeper to include both the arm of the rotor disc and the outer edge where the pads touch. This will put pressure to a larger area and bend the disc slower and less and creating a more wider bend.
Keep rotating the wheel and remarking the bent area until true.
After successfully straightening or truing the bent brake rotor, inspect the brake fluid reservoir and add fluid if needed. Badly bent disc can push out some of the brake fluid out when the pads are pushed further apart.
It’s also a good idea to install a brake disc guard to protect the brake rotor discs from future damage.
Finally, remove the dirt bike from the center stand and test ride. Very small bends in the brake rotor disc will eventually work itself out when riding. If you feel any pulsation or moving brake lever or pedal, repeat the procedure.
Fixing a bent brake rotor is a quick and easy task, even trailside. The modern brake discs are very thin and can bend easily with direct hits, so it makes sense to use brake rotor protection. Remember, most guards can also be bent back.
If you ride more technical single track or regularly ride in rocky or muddy conditions, you should pack a small wrench into your moto maintenance bag. This way you can fix a bent brake rotor out at the camp, not letting it ruin your ride day.
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Last updated: February 24, 2023