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  #11  
Old 05-11-2019, 12:38 AM
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I had the constant air bubbles thing happen to me about 13 years ago on a Cadillac STS...

Only went thru half a bottle until I stopped to think about WTF was going on...

Fluid moving thru an impingement will create low pressure due to Bernoulli principle, the opening of the threads of the bleed nipple internal to the caliper are at 90 degrees to the flow direction, thus will create a slight Venturi & suck in air thru the threads, especially when you're banging on the caliper with a rubber mallet
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  #12  
Old 05-11-2019, 01:12 AM
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Quote:
Originally Posted by Entropy View Post
If you’re regular with brake fluid flushes (every 2 years), cycling the ABS solenoids is unnecessary.
This does not really compute...

The brake system does not have any appreciable flow (at least it shouldn't in a properly working brake system, else you're going to have a really bad day)... When you flush the brake system, you're only removing the fluid that is available to be flowed, which is NOT the fluid that is locked inside the ABS actuating system...

Actuating the ABS system during normal use also does not create flow throughout the brake line system, it only circulates brake fluid through itself via the positive displacement pump & internal bypass system & actuators, it does not circulate any fluid to, or from the rest of the brake line system, nor new fluid from the reservoir... Actuating the ABS system only circulates brake fluid through itself, it does not get new fluid from the reservoir, thus changing only brake fluid, regardless of age, will not appreciably change out any of the fluid internal to the ABS unit, only the tiny amount of new fluid in the passthru channels will get mixed into the old fluid in the ABS unit...

The ONLY way to get the brake fluid exchanged internal to the ABS unit, is having new fluid flowing from the reservoir to the calipers, while the ABS pump is on & actuators are open, as this provides a constant new fluid stream at the locations inside the ABS pump that are opened & pumped thru the ABS unit, where the old fluid is then carried further down the brake lines to caliper & out of the bleed port...

Without the pump actuated, the entire ABS system is completely out of the loop during a brake flush, where the only fluid that is exchanged is the insignificant amount of fluid volume that is in the passthru channels...

If you examine the hydraulic diagrams for modern ABS / traction control units, you'll see that no fluid can be exchanged out of the ABS system, unless the ABS system is actuated while new fluid is being flowed thru it via a pressure bleeder. The ABS module is where there is the most likely chance for contamination of the fluid to occur...

Being very generous with the numbers: Assume that a very generous 10% of the fluid is exchanged out of the ABS unit if you do not actuate it during a flush.

1st flush, you'll have 90% of the factory fill that is 2 years old.

2nd flush, 81% factory fill fluid that is 4 years old, 9% that is 2 years old.

3rd flush, 73% that is 6 years old, 8.1% that is 4 years old, 9% that is 2 years old.

4th flush, 65% factory fluid that is 8 years old, 7.3% @ 6 years old, 8.1% @ 4 years old, 9% that is 2 years old...

Not flushing the ABS unit out, even at 2 year intervals, simply does not compute...

Last edited by SPL15; 05-11-2019 at 01:29 AM.
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  #13  
Old 05-11-2019, 04:33 PM
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Thanks SPL15. I stand corrected!
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  #14  
Old 05-13-2019, 06:07 AM
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Spl, how much of the total brake fluid is held by the abs parts that aren't actuated?

If let's say , guessing here 10% of the total fluid is in those parts, a normal flush would replace 90% of the fluid. During an abs stop, that fluid would be mixed with the rest of the system and not be all old sitting in there anymore.
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  #15  
Old 05-21-2019, 10:38 AM
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He's saying that even when you activate the ABS in action like that, its not like fluid flows freely out of the ABS circuit and into the remaining parts of the system, it moves very little in reality, its just creating brake pressure.

I guess you could go do 20 ABS stops after a flush to try to get some of it to move through, but I am not sure that would even do it.

Agreed, the proper way is to cycle the ABS unit. Did I do it? No, I went to my buddy's garage with a lift and did it manually with NO ABS cycling. I'm fine with that.
Maybe one day when the X5 is in the dealer for something else and its due for a brake flush I'll have them do it by the book.
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  #16  
Old 05-21-2019, 04:56 PM
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The thing about flushing brake fluid is to remove water in the system.
Let's say a bad system has 10% water by volume.
If you change 90% of the fluid, now you have an average of 1% by volume water in the system.
Since brake fluid is hygroscopic, water in the abs system fluid amount will migrate to balance out in the rest of the fluid in short time leading to 1% water all over. That's why in older cars I never had issues with just changing the fluid in the reservoir more often. Water in more saturated sections migrates over to drier sections. Of course in the bmw, I do flushes to change more of the fluid but not everyone has access to ista and my point is that changing a majority of the fluid is the key to preventing water buildup and corrosion.

In cases where water doesn't mix with fluid, like silicone dot 5, the water builds up in the low points as the fluid doesn't "hold" the water like our brake fluid does.
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  #17  
Old 05-22-2019, 10:11 AM
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Agreed, this is the most practical approach for most of us DIY'ers.
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  #18  
Old 06-23-2019, 11:19 PM
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How do you reset the service interval/computer?
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  #19  
Old 06-24-2019, 04:35 AM
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You have to access the "hidden" function on the dash just like for the brake replacement, etc. There are a couple youtube vids on this that show it better than any written response on here. GL.
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  #20  
Old 07-02-2019, 07:24 PM
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I have a MityVac vacuum pump with the brake bleed attachment that I've used previously with success on various Mercedes from 1970s to 2000s. Anybody used on of these on an X5?
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