Brake Bleeding: Pressure vs. Vacuum

[Hofmeister Kink]

What are the pros and cons of using a pressure bleeder or a vacuum bleeder? Has anyone had trouble with a vacuum bleeder? I've heard that a vacuum bleeder can draw air into the system past the brake cylinder seals.

 

[Big Daddy]

I bought a pressure bleeder from a BMW parts wholesaler and love it. Fill it with brake fluid, screw the cover on the master cylinder, pump her up, then bleed each caliper at the wheel, done! I think either one can allow air into the system if you do not stay on top of the fluid level.

 

[Hofmeister Kink]

Thanks, Big Daddy. What I've heard is that vacuum bleeders can draw in air around the brake cylinder cup seals. These seals are meant to work with fluid pressure greater than the outside air pressure. With a vacuum pump, the fluid pressure is below the outside pressure and air can be sucked in around the seals, unless there are cup expanders on. In any case, it sounds like a pressure bleeder is the way to go. Thanks for the advice.

 

[Big Daddy]

That makes sense. The pressure bleeder I bought is wonderful and easy to use.

 

[Ghost]

I’ve read that one can only bleed the brakes on a traction control system with special equipment or by the “stealer,” is this true? Has anyone ever bled the brakes on ASC/DSC with a pressure bleeder without incident?

 

[Hofmeister Kink]

Good question. As I understand it, the ASC/DSC systems work with the ABS system. Pressure bleeders can be used with ABS systems, so I assumed that they may also be used with ASC/DSC as well. What is a "stealer?"

 

[Big Daddy]

I used a pressure bleeder on my 91 750il and she has DSC. No problems! I use it on my 91 318is and 98 M roadster, but neither of them have DSC or traction control. All three have ABS.

 

[Ghost]

What is a "stealer?"

A term referring to dealers because of the prices they charge.

Big Daddy I used it on my ’89 535I but she only has ABS also. I was reading in the Bentley manual that air bubbles might get stuck in the hydraulic system of the ASC/DSC, and it was necessary to use the equipment that actives the system in order to purge these air bubbles. That’s what I was worried about, but if your 750il didn’t have any trouble I don’t see why it would cause a problem. Thanks!

 

[Hofmeister Kink]

THE_GHOST
Junior Enthusiast

Registered: Jan 2004
Location: Chicago
Posts: 23
What I Drive: '98 540i6M Dinan

quote:
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Originally posted by Hofmeister Kink
What is a "stealer?"
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A term referring to dealers because of the prices they charge.

Big Daddy I used it on my ’89 535I but she only has ABS also. I was reading in the Bentley manual that air bubbles might get stuck in the hydraulic system of the ASC/DSC, and it was necessary to use the equipment that actives the system in order to purge these air bubbles. That’s what I was worried about, but if your 750il didn’t have any trouble I don’t see why it would cause a problem. Thanks!


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[Big Daddy]

Wow, I did not know about the Bentley's warning. Would that mean that you could not bleed the brakes with the two person method either? Maybe I got lucky. I will ask a BMW mechanic friend to be sure, but honestly my 750il works great.

 

[frolf]

word is to not exceed 15 pounds of pressure with an automatic bleeder, i heard it gets messy.

 

[Hofmeister Kink]

I got this reply from one of the vendors for a power bleeder:

The factory states that the Power Bleeders are effective at bleeding brakes
with or without ABS and traction control. The unit is very easy to use and,
from my perspective, makes it a joy to bleed brakes. I've used the "pedal
pumping" and Power Bleeder methods and it is night and day. You can see all
the power bleeders on the bottom (scroll down) of the following page:
http://trackhaus.zoovy.com/category/tools.brakebleeders/

Thanks for your email and please let me know if you have any other
questions.

Regards,

Greg
TrackHaus.com

 

[Big Daddy]

Here is the word I got back from Strictly BMW is Bellvue WA.:

"Hey Dan, I just spoke with one of our Technicians, and the main caveat of the DSC systems is making sure that you don't bleed out the whole system, if you drain the system completely, you need a special diagnostic computer to re-initialize the DSC control unit. The system can stand up to a pressure bleeder, and yes, you're correct, 15psi is the highest you want to go.

Brian Terril
Service Advisor
Strictly BMW
(425) 747-6044
brian@strictlybmw.com"

I find you can trust the information that you get from Strictly BMW they have always done a great job on my cars.

 

[Hofmeister Kink]

Thanks again, Big Daddy. I got a reply from the Tech Advisor for the BMW CCA that agrees with your last reply. He says that the chief concern with bleeding brakes on vehicles with DSC is that you NOT introduce air into the system. If you do, you'll need the BMW DIS tester and MoDic or GT-1, which is the "special service equipment" referred to in the Bentley manuals.

And, I believe the better tool to use to prevent introducing air into the system is the pressure bleeder rather than the vacuum bleeder.

 

[Big Daddy]

Bam, another technical question answered throught the cooperative efforts of members of the BMWBoard! Go team!