If your vehicle has soft-feeling brakes, the way to exhaust air from the pipeline is to deflate the brakes. To complete this job, you need a brake bleed wrench or combination wrench suitable for your vehicle's bleed nozzle, a suitable can of brake fluid, a clean glass can and a friend.
Follow the steps below to deflate your brakes:
1. Locate the small nozzles called brake bleed screws located behind each brake.
If you lift the vehicle, it may be easier to access this bleed screw. If you want to climb below, please spread an old blanket or thick newspaper first. If you really want to be more comfortable, you can beg or borrow a creeper to lie on it and slide it easily.
2. Choose a suitable wrench or socket for the screw, and then loosen the screw.
A special wrench called a deflation wrench is suitable for deflation screws, which can prevent the hex head of the screw from rounding. Be careful not to break the screws, otherwise you will need professional repairs. If it gets stuck, spray some penetrant like WD-40 around the screw. After loosening the screw, tighten it again (but not too tight).
3. Put a small piece of flexible hose on the end of the bleed screw, and put the other end of the hose into the tank.
Then fill the canister with brake fluid to cover the end of the hose. If you don't have anything suitable for the vent screw, just place the can near the nozzle so that any liquid sprayed will fall into the can.
4. Ask your friend to slowly step on the brake pedal several times.
Ask your friend to say "down" when you step on the brake pedal, and "up" when you release it.
5. After your friend has stepped on the pedal several times and held the pedal, open the bleed screw.
Brake fluid will squirt (duck!). If there is air in your brake line, air bubbles will appear in the fluid. If you are using the hose-in-tank method, it is easiest to see these bubbles, but without it, you can also see them.
6. Before your friend releases the brake pedal, tighten the bleed screw.
If this is not done, air will be drawn into the brake line when the pedal is released.
7. Tell your friend to let go of the pedal and listen to him or her say "get up."
Repeat this process, loosen the screw and tighten again and again until no more air bubbles appear in the fluid.
8. Open the master cylinder and add more brake fluid until the fluid level reaches the "full" line.
If you break down and have to deflate the master cylinder, this is the same as putting on the brakes (friends and everyone). Just bleed the air at the position where the brake line is connected to the cylinder or the bleed nozzle of the master cylinder (if any).
9. Repeat this process for each brake until air is discharged from each brake line.
After deflating each brake, don't forget to add brake fluid to the master cylinder.
10. After you restore the brake fluid level in the master cylinder to the "full" level for the last time, drive the vehicle around the block.
You should no longer feel soft when you step on the brake pedal. If so, check the master cylinder again to make sure it is full, and try to deflate the brakes again (this situation is not uncommon and will not be as long as it sounds).