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  #1  
Old 09-16-2009, 10:26 AM
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Pressure for Brake Fluid Flush w/ABS

I've seen it stated that flushing the brake fluid in a car with ABS requires up to 30psi of pressure. I've always thought that pressure any higher than about 15psi can pop the reservoir off the master cylinder.

Which is correct, 15 or 30 psi??

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Old 09-16-2009, 11:56 AM
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I pressure bled my W124 with ABS just fine at around 10-15psi
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Old 09-16-2009, 01:12 PM
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That's reassuring. I'm going to flush my 91 300E and my Volvo S80.

According to alldata.com the procedure for the Volvo calls for between 29 and 40 psi when using a bleeding unit. It also says to start with the left front caliper (closest). That also goes against the way I was taught, but I figured it must be a ABS thing.
In the Bentley manual (E-class Bible) it recommends that:
"Caution - On vehicles equipped with ASR, do not attempt to change the brake fluid without using a pressure bleeder capable of maintaining a pressure of 2 bar (30 psi). The fluid and bubbles cannot be effectively evacuated from the system without a pressure bleeder with 2 bar capacity."

Fortunately, my Benz doesn't have ASR.

Last edited by long-gone; 09-16-2009 at 01:23 PM.
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Old 09-16-2009, 01:22 PM
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Quote:
Originally Posted by long-gone View Post
That's reassuring. I'm going to flush my 91 300E and my Volvo S80.

According to alldata.com the procedure for the Volvo calls for between 29 and 40 psi when using a bleeding unit. It also says to start with the right front caliper (closest). That also goes against the way I was taught, but I figured it must be a ABS thing.
In the Bentley manual (E-class Bible) it recommends that:
"Caution - On vehicles equipped with ASR, do not attempt to change the brake fluid without using a pressure bleeder capable of maintaining a pressure of 2 bar (30 psi). The fluid and bubbles cannot be effectively evacuated from the system without a pressure bleeder with 2 bar capacity."

Fortunately, my Benz doesn't have ASR.
Just use a pressure bleeder that hooks up to an air compressor or a vacuum bleeder. Its universally used. btw alldata can be wrong so its good to go by the factory service manual first which states nothing about having a certain psi bleeder
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Old 09-16-2009, 02:07 PM
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I use a Motive Power Bleeder, it works great.....and is capable of 30+psi....though I have never used it much over 15psi....there was no need.
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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 109k - mine - (OC-112,500)
'17 Metris(VITO!) - 29k - wifes (OC-34k)
'09 Sprinter 3500 Winnebago View - 61k (OC - 63k)
'13 ML350 Bluetec - 82k - dad's (OC-86k)
'01 SL500 - 98k(km) - dad's (OC-94,000km)
'16 E400 4matic Sedan - 132k - Brothers (OC-139k)
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  #6  
Old 09-16-2009, 02:32 PM
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Originally Posted by pawoSD View Post
I use a Motive Power Bleeder, it works great.....and is capable of 30+psi....though I have never used it much over 15psi....there was no need.
yeah

The master clyinder and brake lines are capable of handling thousands pounds of hydraulic pressure so you dont have to worry about shooting off the reservoir when you bleed using conventional means
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  #7  
Old 09-16-2009, 07:17 PM
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I have the Motive bleeder as well. I did the Volvo today and went with 15 psi. It seemed to work fine except for a slow leak at one of the bleeder hose connections which I didn't notice until I spotted a puddle of fluid .
It didn't seem to take much fluid, maybe 3/4 of a litre so I'm not sure if the ABS unit flushed out. The manual says the system holds about that much but when you consider the amount of over flow into the catch bottle it probably only took maybe half a litre in the system.
I used the ATE Blue racing fluid for no other reason than it's real easy to see when the new fluid is flowing out.
I'll be doing the Benz later as I saw some steel brake lines that look like they need to be replaced. I'll wait till it needs new pads and I'll overhaul the whole system.
Thanks for the opinions & info!

I believe it is very possible pop the reservoir off the master cylinder if you pump in too much pressure. Unless I'm wrong, while the lines and hardware might be able to handle lots of pressure, the reservoir set-up is generally not designed for much. System pressure builds on the hydraulic side of the MC valve not the reservoir side, which is normally subject to little if any pressure.
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  #8  
Old 09-16-2009, 07:24 PM
LarryBible
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I've flushed ABS brakes in all sorts of cars, MB's included with 15PSI. Where you can sometimes get into trouble is BLEEDING brakes. Occasionally after major hydraulic work where the system is filled with air in one end or the other, it gets stubborn and takes some pressure bleeding before or after using the two man method.

Flushing with 15PSI will be no problem as long as you don't let the fluid level get too low.

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