BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > Did I introduce air into brake fluid

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      11-08-2014, 09:41 PM   #1
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Did I introduce air into brake fluid

I did brake fluid flush today, using a motive power bleeder. I did not put brake fluid in the bleeder, rather I poured fluid directly into the reservior before doing each wheel. However, during the short test drive the brake pedal felt a bit soft.

I am wondering if pouring the fluid directly into reservior would introduce air into the system.

Also, before I start the job I tested the bleeder by pressurising the reservior. It seems the pressure does not last. I could build it to 15psi and it would drop slowly like 1psi every 10 minutes. Is this normal? looks like during bleeding it drops a bit faster than that still.
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      11-08-2014, 10:58 PM   #2
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If you had the power bleeder why didn't you just pour the fluid into the bleeder in the first place and just pressurize it? Taking it off after each wheel defeats the purpose of the power bleeder
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      11-09-2014, 12:11 PM   #3
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The 1psi loss per minute is normal.

If the pedal feels soft, you have an air bubble somewhere, recyrculate the same fluid over and over again until you are satisfied.
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      11-09-2014, 12:34 PM   #4
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outline of steps from the Bentley manual:

1. Top off brake fluid reservoir
2. Connect pressure bleeder to reservoir. Pressurize to approximately 2 bar (29psi).
3. Connect bleeder hose and bottle to right rear caliper.
4. Have a helper hold the brake pedal down.
5. Open bleeder screw, have helper slowly pump brakes about 10 times with screw open, holding pedal down on last pump. When escaping fluid is free of air bubbles close the bleeder screw.
6. Release brake pedal. Refill brake fluid reservoir and proceed to left wheel.

Note the Bentley manual does not instruct one to add fluid to the pressure bleeder, only to the reservoir.

So, I suspect adding fluid to the reservoir wasn't the problem. My read of the manual is it's okay to use the pressure bleeder for "pressure only". There are threads on the forum where people claim to have done the same.
for example:


For me, the real eye opener is they say 'use a pressure bleeder' AND a helper. I bought a pressure bleeder, thinking I could solo it. I used the pressure bleeder and also acted as my own helper. It worked out, but wouldn't do it that way again. Next time I'll use the bleeder and get another person to help.

Why use a pressure bleeder if you already have a helper? I'm not sure but fe1rx on 1addicts gives some thought to it here:

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