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Old 10-01-2020, 07:57 AM   #1
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Brake Fluid

Need to add a little brake fluid for an upcoming short trip. Not able to get Mercedes Benz Dot4+ locally, and wondering if folks have used something other than Mercedes Benz brake fluid?
Thanks for any input.
Sue
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Old 10-01-2020, 09:00 AM   #2
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No need to use MB fluid. The "+" is just their in house designation really. Essentially they want a fluid that has a higher wet boil point than DOT4 does. Thing is, most aftermarket DOT4 synthetic fluids far exceed the minimum wet boil point of DOT4 (around 311).

My advice- AMSOIL Dominator DOT4 (wet boil 410). If that is not available near you, a motorcycle shop should have Motul RBF 660 (399). You may get lucky at the auto parts store and find Liqui Moly DOT 5.1 which you can use also.
Bottom line is that DOT4+ is not some super special fluid. It just refers to the performance when moisture levels rise to 3.7%BV. You can add DOT3, 4, or 5.1 in a pinch. Only those with a lower wet boil point will reduce your service interval of 2 years. Then again, if you actually do flush your brake fluid every 2 years (most don't) then the moisture infiltration is nominal.
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Old 10-01-2020, 09:19 AM   #3
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You might want to find out why you have to add brake fluid..not normally required unless you have a leak.
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Old 10-01-2020, 09:21 AM   #4
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Or used up a lot of brake pad.
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Old 10-01-2020, 11:41 AM   #5
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Old 10-01-2020, 12:40 PM   #6
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Thanks for the quick replies! After reading about brake fluid online, I went and checked the levels on my into town, and in the light of day could see that the brake fluid level was perfect. Guess I just panicked earlier.
Makes sense that I wouldn't need to add brake fluid unless I had a serious brake issue!
Love this forum....thanks for being there!
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Old 10-01-2020, 12:52 PM   #7
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Mercedes Benz is now making brake fluid? Who knew? The Amsoil DOT4+ will cure cancer, or so they claim.

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Old 10-01-2020, 10:19 PM   #8
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Quote:
Originally Posted by Chuck_S View Post
Mercedes Benz is now making brake fluid? Who knew? The Amsoil DOT4+ will cure cancer, or so they claim.

-- Chuck
They dont make a 4+. That is a MB designation, not a standard.
Don't know about cancer, not that they claim it, but I do know the saturated boiling pointof their DOT4 rivals fluid that costs twice as much and I routinely push it to several hundred degrees.
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Old 10-03-2020, 08:02 PM   #9
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Brake fluid is Hygroscopy, meaning it absorbs water.
It absorbs moisture out of the atmosphere.

the longer brake fluid is in your rig, the lower the boiling point.

this moisture not only can case corrosion in the braking system, it can also boil under high heat causing "air" in the system. I have experienced boiling on off road racing motorcycles, but never in a 4 wheel vehicle.


Also as your disk brakes wear, the pistons move closer together since the pads are getting thinner. When they do they end up with more brake fluid in the calipers. You can replace brake fluid in the master cylinder to make up for this.


I would just use any DOT 4 fluid, but I would also follow the MB scheduled brake fluid flush recommendations.
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Old 10-03-2020, 11:59 PM   #10
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Brake fluid is Hygroscopy, meaning it absorbs water.
It absorbs moisture out of the atmosphere.

the longer brake fluid is in your rig, the lower the boiling point.

this moisture not only can case corrosion in the braking system, it can also boil under high heat causing "air" in the system. I have experienced boiling on off road racing motorcycles, but never in a 4 wheel vehicle.


Also as your disk brakes wear, the pistons move closer together since the pads are getting thinner. When they do they end up with more brake fluid in the calipers. You can replace brake fluid in the master cylinder to make up for this.


I would just use any DOT 4 fluid, but I would also follow the MB scheduled brake fluid flush recommendations.
Moisture contamination is controlled in automotive brake systems through the use of a flexible "follower" on the master cylinder. Atmospheric air with its moisture is isolated from the fluid by this rubber like membrane that follows the fluid as it is used in the calipers/wheel cylinders.

When one opens a master cylinder and finds this rubber follower protruding from the cap/cover, don't push it back unless you are going to fill the reservior.
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Old 10-04-2020, 07:09 AM   #11
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So are you saying it don't get contaminated and you don't have to flush every 2 years like MB says?
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