Brake Fluid
Thread Starter
MBWorld Fanatic!
Joined: May 2007
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From: Nebraska
99CLK320,
Brake Fluid
Has anyone swithed over to synthetic brake fluid. I have always read that DOT 4 is the stuff but I also see there is now DOT 5 and synthetic. 5 and synthetic have higher boiling temps so I don't know if it really makes any diff when you apply it to street use. Anybody?
MBWorld Fanatic!
Joined: Apr 2005
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From: SCV SoCal
2002 CLK430
I would have posted earlier, but we’ve had press days at the Los Angeles Auto Show for the past two days. 
This is just my personal opinion, but I don’t think you want DOT5 brake fluid.
DOT5 is a silicon based brake fluid (SBBF). It was designed for vintage cars whose replacement OEM brake parts are made of unobtanium. DOT5 does not absorb moisture hygroscopically like normal brake fluid. Since the water can’t be absorbed by the brake fluid, it pools into little pockets, which corrodes calipers, ABS units, master cylinders, and anything else it comes in contact with.
But wait, it gets worse - DOT5 is incompatible with DOT4. That means all the DOT4 has to be removed from the system. How do you do that? Assuming the entire system (all the hard parts) isn’t being replaced, I’m going to guess a complete line flush (with alcohol?), followed by a complete brake component disassembly and cleaning.
Hold on, there’s more . . . . . . .
DOT5 will give you a "spongier" brake feel. That is because DOT5 is more compressible than DOT4, which is more compressible than DOT3.
There is something called DOT5.1 fluid. 15 years ago, 5.1 was race fluid. It’s compatible with DOT3 and 4, but if you really want the BEST fluid that I know of, grab some Motul 600. It’s available at motorcycle shops. It has a 593 dry rating and 420 cold. I rotate between ATE blue and ATE 200. It’s rated at 536 / 392. I’ve never boiled ATE blue on the street.
On a related note, how is your power bleeder? Mine still won’t work.
This is just my personal opinion, but I don’t think you want DOT5 brake fluid.
DOT5 is a silicon based brake fluid (SBBF). It was designed for vintage cars whose replacement OEM brake parts are made of unobtanium. DOT5 does not absorb moisture hygroscopically like normal brake fluid. Since the water can’t be absorbed by the brake fluid, it pools into little pockets, which corrodes calipers, ABS units, master cylinders, and anything else it comes in contact with.
But wait, it gets worse - DOT5 is incompatible with DOT4. That means all the DOT4 has to be removed from the system. How do you do that? Assuming the entire system (all the hard parts) isn’t being replaced, I’m going to guess a complete line flush (with alcohol?), followed by a complete brake component disassembly and cleaning.
Hold on, there’s more . . . . . . .
DOT5 will give you a "spongier" brake feel. That is because DOT5 is more compressible than DOT4, which is more compressible than DOT3.
There is something called DOT5.1 fluid. 15 years ago, 5.1 was race fluid. It’s compatible with DOT3 and 4, but if you really want the BEST fluid that I know of, grab some Motul 600. It’s available at motorcycle shops. It has a 593 dry rating and 420 cold. I rotate between ATE blue and ATE 200. It’s rated at 536 / 392. I’ve never boiled ATE blue on the street.
On a related note, how is your power bleeder? Mine still won’t work.
Thread Starter
MBWorld Fanatic!
Joined: May 2007
Posts: 1,435
Likes: 0
From: Nebraska
99CLK320,
Do you know anything about synthetic?
On a related note, how is your power bleeder?
I'm just getting around to using it when I replace the brake lines with ss braded. If it doesn't work on my MB I will give it a try on my 72 Alfa Romeo.
On a related note, how is your power bleeder?
I'm just getting around to using it when I replace the brake lines with ss braded. If it doesn't work on my MB I will give it a try on my 72 Alfa Romeo.
MBWorld Fanatic!
Joined: Apr 2005
Posts: 3,784
Likes: 84
From: SCV SoCal
2002 CLK430
Motul 600 is glycol based and advertised by Motul as synthetic brake fluid. I've seen companies advertise ATE Super Blue as synthetic too, although that isn't printed on my liter cans or at the ATE website (that I've seen, it may be buried somewhere on their site). I've read / participated in discussion (argument) boards where some people say that by definition, ALL brake fluid is synthetic. Depending on who's arguing, mineral based fluids "can" be synthetic, along with the glycol based fluids. When it comes to performance, it doesn't matter whether it's synthetic or not (glycol or mineral based). What matters are the wet and dry boiling points and how fast it absorbs water.
