How to bleed the rear brake master cylinder
The rear brakes on many ATVs will have its own master cylinder. To bleed it properly, it is best to remove it and properly bench bleed it.
- Remove the master cylinder assembly including the hose that goes to the rear brake caliper. Use a rag so that you don’t spill brake fluid on paint or plastic.
- Move the whole assembly over to your workbench. Find a way to keep it stable, but be careful if you put it in a vise. The aluminum or plastic materials will break if you apply too much pressure.
- Open the lid of the reservoir and top off with brake fluid.
- Put the free end of the brake line back into the reservoir and start pumping slowly. Only pump about 80% of the overall travel before you start over or you may damage the seals on the piston inside the cylinder.
- Continue pumping until there are no more air bubbles coming out of the brake line, just a steady stream of brake fluid.
- Alternatively, you can direct the free end of brake line into a separate container. Then you need to make sure you add more brake fluid into the reservoir when it is running low. As an upside, this way of doing the job will completely flush the system, replacing the old brake fluid with new.
- Keep the rubber hose submerged in brake fluid when you are done pumping. Clamp down the rubber hose near the caliper fitting to not let any air back into the system. Now you can safely take the hose out of the reservoir and reinstall the cover.
- Reinstall the assembly on the ATV, remove the clamp from the rubber hose and bleed the brakes normally.