How to Bleed Car Brakes?

[DeCaden]

Method for bleeding car brakes: Requires two people to complete. One person sits in the driver's seat and steps on the brake pedal to generate brake pressure. The other person works underneath the vehicle to release the air. The person pressing the brake pedal must firmly depress it and keep it pressed without releasing until the person underneath finishes bleeding the brakes. If a wheel's brake cylinder has issues or a new brake caliper is replaced, bleed that wheel's brakes. If the brake pedal still feels soft after bleeding, proceed to bleed the other wheels' brake cylinders. Always check and top up the brake fluid during the bleeding process.

[Harper]

Last time I changed the brake fluid on my old car myself, bleeding the system wasn’t actually difficult but required careful attention. First, fill the brake fluid reservoir with fresh fluid and leave the cap open. Start bleeding from the wheel farthest from the master cylinder, in this order: right rear → left rear → right front → left front. Get a helper to pump the brake pedal—press it a few times and then hold it down firmly. At this point, quickly loosen the bleeder screw on that wheel’s caliper, and once the fluid comes out without air bubbles, tighten it immediately. Remember, keep the pedal fully depressed and don’t release it! Repeat the process for all four wheels, ensuring the fluid level in the reservoir never drops below the minimum mark—top it up as needed. After finishing, test the brake pedal firmness a few times before hitting the road. It’s best to wear gloves when doing this yourself, as brake fluid is highly corrosive.

[Sylvia]

When it comes to bleeding brake air, understanding the principle is key: air is lighter than brake fluid, so it gets trapped at the highest point in the brake lines. My preferred method is to attach a transparent hose to the bleeder valve and insert it into a plastic water bottle, allowing clear visibility of when bubbles are fully purged. This requires two people working in coordination—one repeatedly pumps the pedal to build hydraulic pressure while the other operates the bleeder valve at the caliper. After each bleed, immediately top up the master cylinder reservoir; letting air enter means starting over. Pay special attention to rear-wheel ABS-equipped cars, as a diagnostic tool may be needed to activate the pump. Don’t rush to drive after bleeding—test at low speed by stomping the brakes firmly; only when the pedal feels hard and responsive is it safe. Older cars often have leaky line fittings, so consider replacing the brake hoses altogether for a thorough fix.

[DelDamian]

Auto repair shops typically use the vacuum bleeding method. By connecting a specialized vacuum tool directly to the brake caliper's bleeder valve, the brake fluid is suctioned out while maintaining a vacuum state to automatically remove air. This method can be operated by a single person, offering high efficiency and minimal risk of introducing new air. Note that the suction pressure should not exceed 0.8 bar, as excessive speed may deform rubber seals. After suction, manually pump the brake pedal 20 times to expel any remaining micro-bubbles. Newer vehicle models now use the pressure bleeding method, where a pressurized canister forces fluid into the master cylinder for more thorough bleeding. In fact, you can DIY with a manual pressure bleeding tool, which costs around 200 yuan and comes with a pressure gauge—far more reliable than manual pedal pumping.

[LeonardoRose]

I've learned the hard lesson of failed brake bleeding all too well: that spongy pedal post-bleeding. Possible culprits include an empty reservoir sucking in new air or ABS pump harboring trapped bubbles. The trick is gently tapping brake lines and calipers during bleeding to dislodge stubborn air pockets. Remember to prepare 2L of fresh DOT4 brake fluid - never mix with old fluid. Lay newspapers to catch spills as contaminated pavement is tough to clean. After bleeding, drive 2km and repeat the process for safety, especially on vehicles with stability control to activate the hydraulic pump. Final reminder: brake fluid is highly hygroscopic - discard opened containers after 6 months.