1. HOME


Brake fluid is essential to your motorcycle’s performance and your safety. Learn when and how to change your brake fluid with Castrol’s maintenance guide.

Motorcycle Brake Fluid

Brake fluid is critical to motorbike performance and safety. Motorcycle brake fluid transfers your squeeze on the brake lever into pressure on the brakes. It’s not a time to compromise and you should look for the best motorcycle brake fluid – one which doesn't simply turn pressure on your brake lever or pedal into compression of the brake callipers, but also has the ability to withstand high temperatures and to protect and lubricate the entire braking system.


You should visually check the level in your brake fluid reservoir at least once a week and top it up with the appropriate specification of brake fluid if it falls below the minimum required level.



We don't recommend changing your brake fluid as a DIY job as the consequences of failing to properly bleed air out of the system can be very serious. The following is a guide to the process that a skilled mechanic will follow in changing your motorcycle brake fluid. The mechanic will use a spanner, a bleed kit and protective gloves.


In preparation for the task, he or she will protect your paintwork as brake fluids will damage painted surfaces.


1. Starting with one of the front brakes, they will open the lid of the reservoir, making sure that the diaphragm doesn’t drop off in the process.

2. Then they will remove the rubber grommet protecting the nipple and loosen the nipple with a spanner so that they can fit the pipe from the bleed kit to the nipple.

3. Next, they will crack the nipple while applying pressure to the brake lever. Once they have done this, the next task is to tighten and release the nipple. They will continue to do this until they see a clear stream of fluid in the see through part of the tube. Once this happens, they will pump the motorcycle brake fluid through tightening the nipple each time.

4. As they reduce the level in the master cylinder with each pump of the lever, they will add new motorbike brake fluid.

5. They repeat this process until the lighter, new fluid is visible in the bleed kit’s see through part of the tube. Now it’s time to tighten the nipple, check the level of fluid in the master cylinder and release the lever. If your bike has twin discs, they will need to repeat this whole process for the remaining front caliper.

6. When they have finished with the second caliper, they will hold in the lever one final time and crack the nipple. If there are no air bubbles in the tube, the job is done and they can re-tighten. The brake lever ought now to feel firm with no sponginess. 

7. Finally, they will top up the reservoir and put the cap back on, making sure the diaphragm is properly in place.

8. They then repeat the whole process for the rear brake.


Motorbike brake fluid is glycol based. Glycol does not boil until very high temperatures have been reached which makes it ideal as the base for a motorcycle brake fluid. However, one of the other attributes of glycol is that it a major absorbent of moisture. As moisture enters your fluid over time through seals and hoses, the boiling temperature of motorcycle brake fluid reduces and it becomes less able to convert force into pressure.

You should consult your manufacturer’s handbook for recommended service intervals but most will recommend that you change your motorbike brake fluid every 1 to 2 years.