ballet_chiq

Hi all –

My next do-it-yourself project is to replace the brake fluid in my ML 430. I have been reading on the internet how to replace the fluid by taking the fluid out from the reservoir, filling it with new fluid, then bleeding each brake at all four corners starting with the brake farthest from the master cylinder. This seems to be the traditional way. I don't know how to do this yet because I don't know what a brake bleeder valve looks like.

Since the principal reason to replace brake fluid is because it readily absorbs water over time, it seems I have found an idea that is simpler and easy to do without having to bleed the system. The idea wastes some brake fluid, but after shopping around, I have found that brake fluid is rather cheap so maybe it is worthwhile to do it this way:

1. Use a rag as a drop cloth around the brake reservoir area since brake fluid is corrosive to a lot of things.
2. Get a clean turkey baster and remove the brake fluid from the reservoir.
3. Clean the brake reservoir and reservoir cover using a very clean cloth or paper towel. Do not leave any particles of lint or dirt in the reservoir or on the cover. Get it as clean as possible.
4. Pour new MB-approved brake fluid to the high level indicator. Cover the reservoir and drive for a few days. The new fluid will readily mix with the old fluid that was left in the brake lines and slave cylinders (the parts of the system that were not drained). As the new fluid mixes with the old fluid, the percentage of absorbed water will equalize to a level that is proportionate to the amount of dilution that the new fluid provides to the old fluid.
5. Do it again; replace the fluid in the reservoir and start driving again.
6. Repeat a third or fourth time as necessary until the absorbed water in the brake fluid is diluted to a point that the brake fluid appears clear, indicating that there is an insignificant amount of water left in the brake fluid.
7. The brake fluid will start absorbing water right away anyways, so water content never really goes to zero. So why bother bleeding, when you can get the water level to just about the same low level through recursive replacement/dilution/replacement/dilution…

Does this make sense, or is there anything wrong with this approach?

mleskovar

The purpose of bleeding the brake fluid is to remove any trapped air in the system. You replace the brake fluid to remove contamination....specifically water. Two separate actions for separate reasons. Your method does not bleed the system. Now, that being said. Your method may work to replace the brake fluid if you do it enough times. Who knows how many times. Just don't remove so much fluid from the resevoir that air is allowed into the system. But then you have new brake fluid that may...or may not...have air in it. Why take the chance? Replacing/bleeding the brake fluid cost less than $100 to be done the right way. A better way is to buy an instrument to check the water content in your brake fluid and only replace it when necessary (if you are worried about spending too much $ on brake fluid replacement).

scorchie

Flushing the brake system is a very easy procedure to do yourself. This is supported by the fact that my local dealership only charges $100 to do the job!

I find the easiest way to do this is to buy an inexpensive power bleeder system. The one that I recommend for people at home is the Motive Products. You should be able to get this for $50 shipped (search the net).

To do the best job, there are a few steps to follow:

1) always use fresh fluid in your power bleeder. Also empty the left over fluid and clean out the power bleeder when done

2) always open a new can of brake fluid. It's not that expensive!

3) don't pump the power bleeder to high! High pressures on the wrong side of the the master cylinder can blow out seals

4) release the bleed valves on the caliper using a SIX POINT WRENCH

5) use a fluid like ATE Super Blue... flush each caliper until blue brake fluid flows! Then the next time, use a gold-colored fluid, and flush each caliper until gold flows. Using alternating colors, you have a good indication when all the old fluid is flushed

6) use a clear tube from the bleeder valve into a container, this reduces spillage

With those steps and some traditional brake bleeding steps (start at caliper farthest from master cylinder, etc.), you can buy all the tools and materials to flush your brakes at home for less money than the dealership charges. It's then very cheap to do it every year or as required. The power bleeder makes it very simple to do, as well.

-s-

Kestas

Unless someone knows better, I doubt there's enough turbulence to mix the fluid in the master cylinder with the fluid in each caliper. Perhaps you could try this method using a fluid with a different color and report back your results. Some people, like scorchie, alternate with ATE blue and ATE yellow every flush.

Another issue that would worry me is that your method wouldn't flush out any corrosion debris or wear debris from the seals/metals. Again, I just don't see where the fluid right next to the caliper piston seal - where fluid is the nastiest - can find it's way to the master cylinder to where you can suck it out.

One method I use to flush brake fluid is to only crack open the bleeder screw, and pump away with the brake pedal. This is a one-man method I use since good help is hard to find in my back yard. There's enough resistance with the bleeder cracked open for good one-way action to move the fluid out of the bleeder. I see no problem with this method when you use a hose to carry fluid away from the bleeder screw.

scorchie

You can replace your bleeder screws with one-way valves so that it makes this easier and less likely to introduce air into the system! Also, using a hose (as you suggest) with your method keeps the air from the bleeder screw, making it less likely for the air to come back in through the screw.

The problem with any manual bleeding method is that without the resistance of the brake calipers, pumping the master cylinder causes movement which is greater than the master cylinder experiences under normal usage. This extra movement, depending on the age of the master cylinder, can cause the seals to move beyond "wear edges" in the cylinder, and cause the seals to fail prematurely. A lot of people do this and say "I never have a problem" but they don't realize that the pedal going closer to the floor (an INTERNAL leak) is a sign of master cylinder failure.

My C43 (purchased used) has pretty much the same brake system as my CLK55. The pedal went very far before the brakes engaged. It was a little disconcerting getting into the car after driving other cars, and have the brake pedal have to go so far before the car stopped. I initially thought it could have to do with a design change of the calipers... I understand that Mercedes changed from square profile caliper piston seals to round profile caliper piston seals. Normally square is used to help pull the brake pads back a bit from the rotor when braking is not engaged. The round seals pull the pads back less. So, I swapped calipers. No change. It turns out after I changed the master cylinder, the problem was solved. I am not sure if it is poor master cylinder design, poor maintenance techniques, or what, but you'll find a lot of Mercedes master cylinders suffer the same issue (search in the forums). So I try to do as little as possible that might cause problems.

-s-