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  #1  
Old 06-10-2003, 12:18 PM
michael cole's Avatar
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dot4 to synthetic brake fluid

has anyone had experience with a switch from dot4 to synthetic brake fluid.i would like to upgrade to a better fluid but have some concerns on compatibility.does the system have to be absolutely free of dot4 before the switch?are there any otther issues that i should be aware of? 1990 300te 4matic
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  #2  
Old 06-10-2003, 12:54 PM
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Good info in the previous post. Here's a write-up that may also be of interest:

http://www.tirekingdom.com/purch/brkfluid.html
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  #3  
Old 06-10-2003, 01:42 PM
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My understanding is that the system needs to be completely free of glycol-based fluid before converting. I would imagine this to be difficult to accomplish witout replacing at least some components.

Compatibility with ABS is suspect.
This was posted on a BMW board from a Teves rep:

">Subject: Brake fluid/E ABS bleeding
>Greetings,
>Following are comments from an ITT/Teves (OEM brake supplier) employee
>to questions I posed on Ate Super Blue brake fluid and bleeding the E36
>brake system with ABS. Thought the list might find it interesting...
>Herman
>********** Message follows **********
>Date: Fri, Jan 13, 1995 1:0 AM PST
>Subj: 3-series brake info.
>To: HermanC2
>Herman,
>Ate brake fluid is glycol based. We at ITT take a rather dim view of
>silicone based brake fluids; the compatibility between your ABS and
>silicone brake fluid is not the greatest. It turns out that the
>hydraulic control unit of your ABS was designed to work with
>conventional (DOT 3 and DOT 4) fluids; silicone fluids can affect
>the sealing performance of some of the internal valves over time. By
>the way, the same applies for other ABS units (Bosch, etc.) too:
>Use only DOT or DOT 4 brake fluid (DOT 5 is the silicone fluid).
>DOT 4 is similar to DOT 3, with the only real difference being a
>slightly higher boiling temperature with DOT 4. Any brand name DOT 3
>or 4 fluid is fine. The newer the can, the better, and don't leave
>the can open in your garage -- it will soak up moisture from the air.
>(That's why you always see the warning "use only brake fluid from a
>sealed container")."


I also saw this article in my travels:
http://www.xs11.com/tips/maintenance/maint1.shtml
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  #4  
Old 06-10-2003, 02:00 PM
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DOT 5:For what it's worth

I put Dot 5 brake fluid in a 1977 Toyota Celica and drove it at least 80K miles over 7 years without doing anything else to the brakes except changing the front shoes once.

My wife had a 1980 Toyoya Corona and I replaced the calipers, the cylinders and changed the brake fluid to DOT 5. It went another 90K with nothing done to the brakes and would have gone further had it not been stolen.

I don't know whether ABS brakes would or would not be a problem, and therefore have not put DOT 5 Mercedes.


If it means that no water gets into the fluid, then the extra cost of the DOT 5 is offset by the elimination of changing the brake fluid so often.

If DOT 5 gets on a brake shoe, my experience is that that shoe will not lock up, as it will with DOT 3. Just rub the rotor and pad with MEK (lacquer thinner).
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1990 300D 2.5 Turbo sedan 171K (Rudolf)
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  #5  
Old 06-10-2003, 02:36 PM
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If DOT 4 is not good enough for you, give DOT 5.1 a shot. It is the next step up from 4 and will work well. I have heard that you would really only notice the difference between 4 and 5.1 on a track and even then, your brakes would fade first.

~dnm
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  #6  
Old 06-10-2003, 03:25 PM
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I do not doubt Richard's results, but question this part:

"If it means that no water gets into the fluid, then the extra cost of the DOT 5 is offset by the elimination of changing the brake fluid so often."

I do not expect that DOT5 does much to prevent water from getting into the system in the first place, just that water acts differently once it gets there. Braking systems are vented to the atmosphere, and rubber hoses are somewhat permeable. My understanding is that the concern with DOT5 is that while the water that does enter the system will not dissolve into the fluid, it will instead settle in the low points, and cause corrosion or vaporization problems.

For this reason, I would speculate that DOT5 would require more frequent flushing, not less. Perhaps not the entire system, but enough to purge whatever water has settled into the calipers.
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  #7  
Old 06-10-2003, 05:03 PM
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I'd never use Dot-5 in a car unless it was designed for it. Between potentisal rubber seal incompatibility, difficulty in bleeding air bubbles, potential water damage and the need to completely flush the system it doesn't seem worth it. What is the expected benefit? Regardless of the type of fluid it should be changed at least every year anyway....depending on driving style, tracking the car etc.

After that the brake lines (rubber) should be replaced periodically as they "stretch".

My recomendation is to use a pressure bleeder so flushing and/or bleeding on a regular basis is simplified and use a high-quility brake fluid. Like ATE Super Blue (if you can get it) or Castrol SRF (if you can afford it).
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  #8  
Old 06-10-2003, 06:01 PM
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What caused me to put DOT 5 in the Toyota in the first place was the fact that within 3000 of the time I bought it at 40K, the front and the rear brakes had both leaked, and of course then I had to change BOTH cyinders and BOTH calipers and so when the master cylinder started to leak, I said the hell with this and flushed the system and put the DOT 5 into it. Perhaps the problem was the quality of the rubber brake parts made for the Toyotas.

I have had no problems with the brakes on either Mercedes and have since begun to drain and replenish the DOT 4 fluid every 2 years.

Before this, I had never heard that brake fluid ever needed replacing. It seemed pretty nasty looking to me, and I suggested that it needed to be changed, but the mechanics would just say īt just gets like that".

Of course this was back when the mechanics I came in contact with were pretty much 8th grade dropouts.

I have never had a problem with boiling brake fluid or brakes fading: not too many mountains in FL.
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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)
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  #9  
Old 06-11-2003, 12:10 AM
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I understand the stuff has a strong following among the collector car set, since these sorts of cars tend to sit in storage for extended periods. I guess glycol-filled systems do not tolerate sitting still very well. I have indeed seen calipers seized permanently in place after extended storage. Must be something to this...

Perhaps some day when I strike it rich, my E-type roadster will be filled with DOT5...
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