I recently took my 86 300e in to the shop to get looked over in preparation for a long road trip and one of the things they said was the brake fluid looked very old and dirty. They suggested I get a brake fluid renewal to clean everything up and ensure proper functioning of my brakes. When I told a friend of mine that they had suggested this, he kind of laughed at me and said he’d never heard of such a thing. How does brake fluid get dirty, he said. So is this a common procedure? Or are the mechanics’ trying to take me for a little ride?
A 1986? If this still has the original brake fluid in it, it’s way over-due to be bled.
Brake fluid absorbs moisture from the air. Over time, enough moisture builds up where it starts corroding brake components. Moisture in the brake fluid also lowers the boiling point of the brake fluid.
So brake fluid gets dirty from the amount of moisture it contains, and the result of moisture corroding the brake components.
Tester
I agree with tester, and would add that brake fluid that old will also start to look black because of the rubber seals in the system deteriorating, and polluting the fluid. I would also change it out.
Thank you both for your explanations. It makes sense. So, is this something I could do myself fairly easily? Or is it best left to the pros? Thanks again.
Take it in let someone else try to bleed the brake system. With the age of the vehicle, there’s a good chance that one or more of the bleeder screws are going to be difficult to open. Better that they deal with that than you.
Tester
I just checked the original maintenance schedule for my 83 benz and it require the brake fluid to be renewed every year. That may be overkill with current synthetic brake fluid, but once every couple of years is probably still appropriate.
Do you have the maintenance book for your car, I’m curious what it says?
Unfortunately, I don’t have the maintenance book. Do you happen to know where I could pick one up? I’ve looked on e bay but haven’t had much luck. I’d imagine I could contact a dealer for one, but I don’t want to pay an arm and a leg.
Good God, man. Get that fluid flushed and replaced TODAY. Brake fluid does indeed get dirty over time, and it absorbs moisture from the air (your master cylinder reservoir is not sealed). That water collects in the lowest part of your system, where it can freeze or corrode brake pistons, etc. Fluid should be totally replaced every two years, or more often.
It’s pretty easy. Bavarian Autosport, among other suppliers, sells a one-man bleeder that works from under the hood. You take off the brake reservoir cap, put on the bleeder, pump up the pressure, then bleed from each wheel in turn until the fluid runs clear and free of bubbles. I’d recommend a liberal soaking of each bleed screw with PB Blaster for at least two days before trying to loosen the bleeders, if it really has been a long time.
I would check with the dealer, I suspect you can get one for a nominal cost. Maybe they will just print out the service schedule for you, especially if they think you will go to them for some service and/or parts. I have found their dealers to be pretty interested in customer service.
Edit: I found your service manual, go to this link and click on “Technical Literature” under the “Classic Center” tab. Enter the info for you car and you will find the maintenance booklet for $19.99. It looks like they have most of the manuals available back to 1946:
Although my owner’s manual says nothing about changing brake fluid, it generally has a life of about 30,000 miles. Yes, get the brake lines flushed.
Wow, that’s fantastic! Thank you. I live in a small town, so the closest dealer is a 2 hour drive. There’s a good shop here that specializes in Mercedes Benz though. I just wish I could afford to pay them to do all the work I need done. It may be time to learn how to work on cars. 
If you really want to work on it yourself, talk to these guys: