If it was a brown ring shape then it was the original filter from manufacturing the car. It is washable and reusable. I had the same in my 300TD but chose to use the new style filter instead.

Dave

It's inside the fluid reservoir on the 123's. Probably there in yours also.

The eighties up through mid to late nineties p/s systems have seals that will be attacked by Dexron ATF. The most economical and very acceptable fluid is just plain old Power Steering fluid from the auto supply store.

The system should be PROPERLY and THOROUGHLY flushed. Removing what's in the reservoir and replacing it will do virtually NOTHING.

What I call the "ASE Test Method" for flushing the power steering fluid is very easily and quickly accomplished on 123 and 124 MB cars. Unlike many other cars, these cars have a filter that should be changed when doing this procedure. Replace the filter after the flush portion of the procedure but before refilling the system during the procedure. With the reservoir empty you will see the filter at the bottom of the reservoir. It is shaped like a hockey puck with a hole in the middle.

The flushing procedure requires about four quarts of P/S fluid, two of which will be flushed through the system and disposed of and then the other two will be used to refill the system.

Remove the return line to the P/S pump and lower it down into a drain pan. Plug the hole from which you removed the return line. With the two quarts of fluid opened and at hand, have an assistant start the car and begin turning the steering wheel back and forth lock to lock. As the reservoir level goes down continue to pour the two quarts of fluid into the reservoir while engine is idling. As soon as the fluid is all gone AND the steering wheel can no longer be turned easily, the assistant must shut off the engine.

At this point replace the filter, put the return line back in place and fill the reservoir. Don't let the assistant go back in the house yet. Have the assistant start the car and again turn the wheel back and forth as you slowly fill the reservoir. Keep turning the wheel back and forth to bleed the system and draw fluid from the reservoir until it is full.

After driving the car around the block or back and forth to work once, recheck the fluid.

This is the best 20 minutes you will spend to maintain your p/s system.

Good luck.

If it's done enough times, though, one could almost entirely replace the fluid, right? What's the downside of this, assuming it's done repeatedly? Then, as a way of maintaining, just drain and refill the reservoir at whatever interval.

Just trying to understand....

I am not a DIY type but after reading your post I am ready to try this on my 240D 77, where/which exactly is the return line to the P/S pump? would you be able to describe the line location?

Vahe
240D 77 350K

it is the hose with the hose clamp on it, not the hose with the crimp on pressure line...
John

You'd never have entirely "fresh" fluid and would remove newer fluid along with older fluid. You'd end up using more fluid than necessary in exchange for a bit of labor savings, but by the time you factor in the number of times you'd have to do it, the labor would probably be a wash.

For example, let's say system "X" contains ten quarts of fluid (ten is convenient here for the math), and let's say that between each exchange of one quart, the "old" fluid stays "old" and the "new" stays "new."

Change 1)

- remove one quart of mixed fluid, replace with one quart of new
- the removed fluid is 100% old
- you end up with 9 quarts of old, 1 quart of new

Change 2)

- remove one quart of mixed fluid, replace with one quart of new
- the removed fluid is 90% old, 10% new
- you end up with 8.1 quarts of old, 1.9 quarts of new

Change 3)

- remove one quart of mixed fluid, replace with one quart of new
- the removed fluid is 81% old, 19% new
- you end up with 7.3 quarts of old, 2.7 quarts of new

... and so on, ending up with these amounts after each change:

Change 4) 6.6 old, 3.4 new

Change 5) 5.9 old, 4.1 new

Change 6) 5.3 old, 4.7 new

Change 7) 4.8 old, 5.2 new

Change 8) 4.3 old, 5.7 new

Change 9) 3.9 old, 6.1 new

Change 10) 3.5 old, 6.5 new

So, after ten changes using a total of 10.0 quarts, you only end up with only 6.5 quarts of new fluid, whereas if you'd changed it out in one session, you'd have 10.0 quarts of new fluid. It would take a long time and many changes to even approach a total changeout. Yes, the proportion of changeout on the real system we're talking about would be higher and you'd approach the asymptote more quickly, but the point is still the same.

Put another way, one job done halfway, plus another job done halfway doesn't equal one job done completely.

not to mention that all the left in new fluid, becomes dirty and contaminated when it contacts and mixes with the old fluid...
John