Does a Mercedes require special brake fluid?

[Scott98]

I'm going to put new rear calipers on my '85 this afternoon. I'm also going to flush the break fluid. Do I need any special kind? Will any DOT 3 do the job?

Scott

[Jim Dandy]

I believe most require DOT 4.

[Scott98]

There's no special MB brand or anything like that is there?

Originally posted by Scott98
There's no special MB brand or anything like that is there?

I'm sure there is. It likely costs 3-6x as much as the exact same DOT brake fluid you can get at Wal-Mart.

[Scott98]

That answers my question then. Thank you very much. I'm off to put new calipers on my car and change the brake fluid.

Scott

Last time I bled the system I used "Bremflussigkeit".

$7.77 for 1 liter at the "Fastlane" here. I ordered because I was ordering about $300 worth of other brake parts, so what the heck. Plus, Walmart sucks. I like to support my guys here, as Phil at "Fastlane" is awesome.

[ericnguyen]

Dear Scott98:

Virtually all Mercedes (possibly except very old ones) require DOT 4, even those as old as 25 years. You can read the DOT requirement printed on the clear brake reservor's cap.

The difference between DOT 3 and DOT 4 is the presence of some extra additives in DOT 4 to make it less hygroscopic (absorbing moisture) than DOT 3. These additives also give DOT 4 higher DRY and WET boiling points, which are necessary for hard braking situation.

Yes, you can also use DOT 3 on your older Mercedes cars, but you need to change it more frequently than DOT 4. DOT 3 and DOT 4 are compatible with each other.

Do never use DOT 5 (silicone-based) brake fluid on Mercedes-Benz cars. It will deteriorate all the rubber lines and seals/grommets in your brake system very quickly. However DOT 5.1 is not silicone-based. In fact, DOT 5.1 is fully synthetic and backward-compatible with DOT 3 and DOT 4. DOT 5.1 may have even higher DRY and WET boiling points than DOT 4. However, the main reason for the existence of DOT 5.1 is the fact that its viscosity is low enough to provide better brake fluid circulation at very low temperatures, or in highly sophisticated anti-lock braking systems found on modern cars (MB cars have ABS as early as 1986). Those ABS systems have lots of tiny tubes and micro-valves which require a good circulation of brake fluid (lower viscosity).

In summary, if you drive an old Mercedes-Benz (before 1985-1990) and drive like a grandma, you can use DOT 3. But if you have lots of hard braking, drive aggressively, or use your car for towing or mountain driving, you'd better off using DOT 4, or even better DOT 5.1. Forget about DOT 5.

BTW, silicon-based DOT 5 brake fluid has a higher compressibility coefficient than polyglycol-based DOT 3, DOT 4, and DOT 5.1. Therefore, for cars or motorcycles (mostly Harley-Davidson) that are designed to use DOT 5, pressing the brake pedal will give you a mushy or somewhat elastic feeling. On the contrary, DOT 3, DOT 4 and DOT 5.1 give you much more precise and articulate braking feeling thanks to their very low compressibility.

The only major advantages of silicone-based DOT 5 brake fluid is that it absorbs very little moisture, and it does not destroy car paint if it gets spilled over.

Last but not least, NEVER accidentally pour (even a single drop) of power steering fluid, ATF, engine oil or any other oils in your brake reservoir. It will ruin your brake system miserably and you will have to replace lots of its rubber lines and seals etc.... It's very time consuming.

Best regards,

Eric

[JHZR2]

excellent post, eric.

Use a DOT4. the european car companies have been using it for years. Why GM still uses dot3, and doesnt reccomend a typical brake fluid flush schedule amazes me.

That doesnt mean that itll do any wonders, were not racing, but youll know that itll stand up to braking heat better. Auto-xers and driving schools require brake fluid flushes at least every 6 months for that reason.

some may claim that itll save your brake system, but Ive seen well cared for, flushed master cylinders and abs units ruined by 40k despite flushes, and Ive seen sensitive parts go on with junky fluid that had crap floating in it.

But the brake system isnt something to mess around with, and there is a reason why the euro car companies reccomend brake fluid flushes every 1-2 years. So Id do it, and use a good fluid. ATE SL fluid (available here) is a top uality fluid. ATE super blue racing is about $1 per liter and has a much higher wet and dry boiling point. Plus they make the super blue and then a 2000' fluid which are both exactly the same. This setup is great because you have positive identification of a thurough flush if you change between the colors...

For a good OTC fluid, Id use castrol GTLMA dot4. My local BMW/honda/pontiac/gmc/volvo uses that exclusively.

JMH

[prb51]

My 42 year old 190sl requires DOT 4. I believe all of the 50's era vehicle use it.

[strelnik]

Originally Posted by BlackE55

Last time I bled the system I used "Bremflussigkeit".

.

That is the German translation of " brake fluid."

[Jeremy5848]

Originally Posted by ericnguyen

Last but not least, NEVER accidentally pour (even a single drop) of power steering fluid, ATF, engine oil or any other oils in your brake reservoir. It will ruin your brake system miserably and you will have to replace lots of its rubber lines and seals etc.... It's very time consuming.

Best regards,

Eric

Pouring brake fluid into the power steering reservoir is also harmful, as I learned the hard way earlier this year.

Jeremy

[rocky raccoon]

Those posts are 11 years old guys.

[mannys9130]

The OP ought to have flushed his fluid 5 times by now. Hahahaha

[BillGrissom]

I would say opinions have changed since the first post. Strange that a 50's car would need the fairly new DOT 4. I thought DOT 4 can absorb more moisture (why it is better). I use DOT 5 in both my M-B and my old Mopars. The pedal is hard and it doesn't degrade the rubber (strange myth, some 50's British cars required silicone since glycol degraded the rubber).

[RunningTooHot]

Hey Guys (Including those from 11+ years ago)

Just an FYI on Dot 5 / silicone fluids:

Due to very myopic thinking, people seem to think that silicone (DOT 5) fluid is better because it isn't hygroscopic. Counter-intuitively, you WANT your brake fluid to be hygroscopic and hold the water in suspension! Why? Because when the water is held in suspension, it is easily flushed out with a fluid exchange. Then you have a completely water-free system. (For a while, at least. )

Any water that gets into a system filled with silicone based fluid settles out at low points and over time will cause localized corrosion. You could have a brake line eaten away, or other nastiness such as when the water pools in the low point in a caliper, eating away at the lowest part of the piston.

Rough corroded piston surfaces combined with caliper piston seals does not make for a happy marriage. You may notice a slow seep, but if you don't, you could be really screwed. You NEED your brakes to work under severe circumstances, i.e., panic braking - which is when the pressure will rise much higher than usual... and that is when the marginally sealed surface could fail catastrophically. Pop!... (Insert sound effect of twisting sheet metal here.) Luckily, modern dual/split braking systems will still give you half the braking capacity, but...

The problem is that when you flush the system, the water remains in the low points because the physical "scrubbing" effect of the fluid movement is not enough to remove the water in a caliper. (The bleeder screws are at a high point, for obvious reasons.) The brake lines will usually clear, but that water just gets translocated to the caliper.. (Do I even need to mention what happens when/if that water in the caliper boils under hard use?

Bottom line is that DOT 5 is great for specifically designed applications, and also for race cars that see a full system rebuild on a regular basis. But for street cars... not so much.