Vacuum Brake Bleeder Tip

[The Critic]

I normally avoid using my pneumatic vacuum brake bleeder for fluid exchanges since it results in a soft brake pedal. For some reason, the vacuum bleeder will often allow a small amount of air to enter the brake caliper.

I recently found that if you allow each caliper to gravity bleed for at least one min, most of the trapped air will come out.

I made a video of the process. In this video, you will see me turn off the pneumatic brake bleeder and remove the collection hose. After removing the hose (0:03), it takes about 15 seconds (0:18) before fluid begins to drip out of the bleeder screw - this is due to the trapped air inside of the caliper. As fluid drips, you may be able to see a small air bubble at the opening of the bleeder screw. After about 30 seconds of dripping (0:52), the bubbles disappear.



Does it work? Sort of - the pedal still ends up a bit softer than before I completed the service. It did seem to firm up a bit after the test drive, so perhaps the vacuum process causes the fluid to aerate a bit?

 

[Sequoiasoon]

I never had luck with the vacuum bleeders, always slightly soft pedal afterward. I do much better with the Motive pressure bleeder or old school 2 man with help from my kids/wife/whoever.

 

[Soft Cars]

Most shops will have a pressure bleeder that pressurizes the master cylinder.

 

[Jetronic]

I normally avoid using my pneumatic vacuum brake bleeder for fluid exchanges since it results in a soft brake pedal. For some reason, the vacuum bleeder will often allow a small amount of air to enter the brake caliper.

I recently found that if you allow each caliper to gravity bleed for at least one min, most of the trapped air will come out.

I made a video of the process. In this video, you will see me turn off the pneumatic brake bleeder and remove the collection hose. After removing the hose (0:03), it takes about 15 seconds (0:18) before fluid begins to drip out of the bleeder screw - this is due to the trapped air inside of the caliper. As fluid drips, you may be able to see a small air bubble at the opening of the bleeder screw. After about 30 seconds of dripping (0:52), the bubbles disappear.



Does it work? Sort of - the pedal still ends up a bit softer than before I completed the service. It did seem to firm up a bit after the test drive, so perhaps the vacuum process causes the fluid to aerate a bit?

The vacuum tends to retract pistons. If it aerated the fluid, it wouldn't get any better with time: air in the system can't get out.

I found that every time you get significant amounts of air in the brake system, like replacing or rebuilding a caliper, it pays to bleed the abs unit with software.

 

[eljefino]

I use a hybrid method of the "driver stomp" along with the vacuum bleeder, but the bleeder is just for cleanliness. I'd probably have as good luck with the half-full gatorade bottle and hose.

 

[Ihatetochangeoil]

I never had luck with the vacuum bleeders, always slightly soft pedal afterward. I do much better with the Motive pressure bleeder or old school 2 man with help from my kids/wife/whoever.

I LOVE my Motive pressure bleeder. I've used it enough to realize that I need to replace the rubber washer that seals to the MC every time I use it. As a precaution to leakage, I also put a large drain pan under the car and MC, just in case. The Motive bleeder together with speed bleeders, my opinion is I get as firm a pedal as if the vehicle were new, and I DON'T need my wife or a buddy.

 

[Traction]

I've been using an OTC air-powered vacuum bleeder for 20 years many times on completely dry systems and it has worked every time. The air bubbles leaking around the bleeder screw threads do not go back into the caliper since it's after the fact. The whole idea is to get brake fluid moving through the system taking the air with it. The vacuum bleeder can pull a pint of fluid through the lines in very little time, and it only take about a pint per corner. Takes less than 30 minutes usually to bleed everything.

 

[Luftmasse]

I don't see any extra air coming out from tapping with the hammer. Does this part really makes a difference?

 

[The Critic]

I've been using an OTC air-powered vacuum bleeder for 20 years many times on completely dry systems and it has worked every time. The air bubbles leaking around the bleeder screw threads do not go back into the caliper since it's after the fact. The whole idea is to get brake fluid moving through the system taking the air with it. The vacuum bleeder can pull a pint of fluid through the lines in very little time, and it only take about a pint per corner. Takes less than 30 minutes usually to bleed everything.

Every vehicle I have used a pneumatic bleeder on….a small amount of air will come out if I follow up with a manual bleed. The quantity is usually very minimal if I allow each caliper to gravity bleed for 1-2 min after the pneumatic fluid exchange, but it’s still there.

 

[edyvw]

Always returns firm brake pedal:

 

[The Critic]

Always returns firm brake pedal:
View attachment 188749

The disadvantage of that method is you’re contaminating the fluid with air.

 

[edyvw]

The disadvantage of that method is you’re contaminating the fluid with air.

Hmm, with a pressure bleeder? How? Where does air end up since it returns the normal braking operation? Actually, in ISTA manual, BMW specifically instructs to use a pressure bleeder!
The only time air was introduced into my braking system is via vacuum bleed done by a guy who was doing something on rear suspension when I did not have time. I told him, if I ever give him car again, ask me for pressure bleeder as there is no way I will take car from him if he does it using vacuum.

 

[The Critic]

Hmm, with a pressure bleeder? How?

The fluid is being pressurized in a chamber. When you do so, the fluid is absorbing the air from the environment, which is not dry.

Actually, in ISTA manual, BMW specifically instructs to use a pressure bleeder!

They are probably specifying the usage of an electric pressure bleeder or a diaphragm style. The diaphragm style will store the fluid inside of a bladder and the air does not contact the fluid.

The electric bleeders use a pump.

 

[edyvw]

The fluid is being pressurized in a chamber. When you do so, the fluid is absorbing the air from the environment, which is not dry.

They are probably specifying the usage of an electric pressure bleeder or a diaphragm style. The diaphragm style will store the fluid inside of a bladder and the air does not contact the fluid.

The electric bleeders use a pump.

Wait, are you talking air bubbles or absorption of the air moisture bcs. nature of the fluid? There is NO AIR as the membrane will seal the reservoir. Now, this is MUCH easier to do on Euro cars as they all have same reservoir and universal membrane. On Toyota, I found it harder to do it with those adaptors which could lead to air pockets.

ISTA specifies this pressure bleeder. In case of replacement of Master Cylinder, and calipers, a manual pressure bleeder is to be used. Once pressure is set, ISTA is activated to get rid of bubbles on DSC module valves. In case of fluid flush, pressure bleeder alone is sufficient. When I had air pockets due to the vacuum bleed procedure, I had to use the ISTA method as the guy managed to screw up the whole system apparently. SImple pressure flush could not do it.

 

[The Critic]

Wait, are you talking air bubbles or absorption of the air moisture bcs. nature of the fluid? There is NO AIR as the membrane will seal the reservoir. Now, this is MUCH easier to do on Euro cars as they all have same reservoir and universal membrane. On Toyota, I found it harder to do it with those adaptors which could lead to air pockets.

When you pump up the pictured pressure bleeder, the tank is pressurized with air. Air that is drawn in from the environment.

That’s the issue.

 

[edyvw]

When you pump up the pictured pressure bleeder, the tank is pressurized with air. Air that is drawn in from the environment.

That’s the issue.

So, you are talking about moisture due to the hygroscopic nature of the fluid?

 

[The Critic]

So, you are talking about moisture due to the hygroscopic nature of the fluid?

Correct.

If you use a bleeder with a bladder or an electric one, less likely to have this issue.

 

[edyvw]

Correct.

If you use a bleeder with a bladder or an electric one, less likely to have this issue.

I am not sure how would you force more moisture into the fluid compared to let's say opening the cap to add fluid. I am not a chemist, but if you vacuum, you still need to open a cap and add fluid that is exposed to outside air.

 

[The Critic]

I am not sure how would you force more moisture into the fluid compared to let's say opening the cap to add fluid. I am not a chemist, but if you vacuum, you still need to open a cap and add fluid that is exposed to outside air.

When you pressurize a chamber, the air is being forced into the fluid. At least that’s how I understand it. Otherwise, how does the fluid stay pressurized at 15-20 psi?

 

[edyvw]

When you pressurize a chamber, the air is being forced into the fluid. At least that’s how I understand it. Otherwise, how does the fluid stay pressurized at 15-20 psi?

The air is sucked out of the reservoir and pressurized by new fluid. You have to fill the bottle. In instructions, it clearly states not to allow the bottle to get too low on fluid so that air is not introduced into the system.