How to Bleed the Brakes Using a Vacuum Pump

How to bleed the brake using a vacuum pump. This was an old video I produced back in 2016 and with some of the questions I’ve had over the years, I’ve decided to upload an improved version. As some of you may have seen, I did rebuild the front calipers on this truck and if you haven’t seen that video, be sure to check it out. Whenever any work is done on the brake system where there’s fluid involved such as replacing a caliper, brake line, wheel cylinder, master cylinder, etc, the system will need to be bleed off air. This tool can also be used to flush a brake system, removing the old fluid and I’ll show you that in a moment as well. #brakes #bleedingbrakes #autorepair

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Tools/Supplies Needed:
-vacuum pump kit
-clean rags
-drain pan
-wrench
-brake fluid

Procedure:
The master cylinder is located on the driver’s side of the truck, therefore I need to start with the further affected wheel first. I always like to loosen the bleeder screw first using a 6 point socket. Make sure the master cylinder reservoir is full of fluid, up to the maximum line.

Depending on the vehicle and how much fluid was drained from the system, the ABS pump may need to be activated for the system to be fully bleed.

Have a drain pain handy, along with a clean rag. Install the box end side of the wrench of the correct size on the bleeder screw, also ensure it has enough movement and doesn’t catch up on anything when tightening and losing the bleeder screw. The hose from the vacuum pump should fit tight on the bleeder screw.

Pump up the vacuum to about 20 to 30 in hg. Being that there’s no clamp around the bleeder screw, there might be a small leak which is fine. Make sure there isn’t a large leak.

Open the bleeder screw and watch for fluid. If no fluid is coming out of the bleeder screw, it can be plugged with rust and dirt or you may not be opening it enough.

The vacuum pump can be pumped up while the bleeder is open or you can close the bleeder screw, pump up the vacuum, then open it again. Don’t let the vacuum go below 10 in hg. As long as there is negative pressure at the bleeder screw, there is minimal risk of introducing air into the brake system.

When bleeding air in the system, you’ll notice excessive bubbling in the fluid which is normal. This bubbling will change when the air is removed from the system, either being greatly reduced or completely disappearing. This can be easily spotted with the clear hose.

It’s common for bleeder screws to leak around the threads too when it’s open, but as mentioned earlier, as long as there’s negative pressure at the bleeder, air cannot be pushed back into the system.

Considering this truck is also new to me, the fluid does appear to be older, I have decided to flush the front half of the system while I’m here. Vacuum pumps can also be used for removing old fluid too. Brake fluid new will have a light golden color. As brake fluid gets older and components deteriorate in the system, it’ll become discolored. You’ll notice the change in color between the new and old fluid when watching the extraction.

The amount of fluid that is removed from the system, either from removing the air or changing the fluid does vary depending on the work. If a whole line was replaced from front to back, more air would be present in the system. If you were flushing the fluid, the further wheel from the master cylinder would have the most fluid removed.

For this, I had the whole cup filled with fluid. Make sure the cup doesn’t become overly full where the brake fluid gets sucked into the pump, so drain as needed.

When done, tighten the bleeder screw while the vacuum is still present. To keep things a little cleaner, I usually pump up the vacuum and slowly remove the line, so any brake fluid will be sucked back into the reservoir.

Then check for any leaks.

Check the fluid level in the reservoir and add more as needed. Moving onto the next closest wheel, this would be the last wheel for me, this is the front driver’s side, use the same process.

When done, the key can then be turned off and tighten the reservoir cap. Check the brake pedal. The pedal should be firm and not sink to the floor. If it’s soft, then air is still present in the lines and you will need to re-bleed the system.

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