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1983 300TD Turbo
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Discussion Starter · #1 ·
Just finished replacing a set of accumulators on my wagon. I am a lot happier with the ride. It was a beautiful day yesterday, so being under the car was not horrible. It took me about 5 hours total (including babysitting my daughter and her Playdoh).

I think that I must have blown out the accumulators when I overloaded my wagon with 400 lbs of ledge stones. Anyway, the ride has been very bouncy.

First, I did some diagnostics:
1. Checked for leaks at the tank, pump, and all hoses under the engine (all dry)
2. Jacked the car up onto jack stands with cement blocks as a back up (paranoid and safer)
3. Checked all of the hoses under the car, the accumulators and the struts (all dry). I did waste about an hour trying to access the suspension through the floor as I saw something on a post that led me in that direction. Under the car is the way to go except for the strut removal which I fortunately did not have to do.
4. I tightened the adjuster screw (LH one end / RH the other) and lowered the car. It was now riding higher. I then got the handle of the jack and actuated the system up and down. It was working fine.

I guess the reason why I did all of this diagnostic crap was that I did not understand how a ruptured bladder in an accumulator would leave a ride bouncy. Also my little book from mercedessource.com takes you on that route. I thought that alll of the N2 would have been burped from the system and the struts would be rock hard due to the incompressible hydraulic fluid. The other thought was that the N2 would be leaking out of the bladder but be of the same volume and have the same compression or dampening effect. Anyway, I still don't get it, but would have to wager that there is less gas in the accumulators than there was supposed to be (they were as full of hydraulic fluid as a coconut is of milk).

For the removal, I first bled off some pressure at the bleeder on the valve. Looking back, I probably should have let the system drain through this bleeder to allow for a more sanitary removal job.

I then went to work on the passenger accumulator. My left hand is not nearly as strong as my right. In hindsight, I might have been better off trying to get under the car in a different orientation so that I could have used my strong right hand.

First, I loosened the three 13mm mounting nuts on the left just so that they were able to be removed without much strain. I then broke out the big 17mm hex bolt on the line to the strut. This 17 mm was real tight and requires the mounting nuts to be pretty tight. A cheater pipe is handy. I then broke out the 11 mm retainer nut on the high pressure line from the pump. This started the dripping of all of the hydraulic fluid that was in the accumulator. It took a long time to get all of this fluid out into my topless milk jug. Loosening the 17 mm fitting helped a bit. One thing that I found was that the strut does not leak back much fluid as the tires are down holding a vacuum on it.

Once it was drained out for the most part, it is just a matter of taking everything out and putting the new accumulator in. I did not worry about leaving air in the system as my book says that the system is self burping.

The right hand side was much easier as the learning was behind me. I was quicker to completely pull off the high pressure line. The fluid is for the most part is coming from the accumulator and not from the valve side of the system. The sooner you pull the high pressure line the faster the accumulator will drain.

Once I had everything plumbed up, I triple checked everything to be tight. I also wiped all the fluid off so that I would be able to see if there were any leaks. I also put the adjuster screw into about the same gap as initially.

I had added about half a liter of MB hydraulic fluid to the system prior to my repairs. I had bled off about 3/4 of a liter into my milk jug. Prior to starting the engine again, I checked the fluid to be at about max, but added the other half liter of hydraulic fluid as I assumed that it would want to drink all that I bled out. This did not really happen as the bladders on the new accumulators are not ruptured.

When I started the engine the back bumper still seemed to bounce. I sat down on the back bumper about 60 times trying to burp all of the air back out to the tank. I then went for a ride. The suspension is now working great. My wife says that the car rides much better than her 1997 528i. Anyway, the amount of bounce in the rear bumper is a little less. I guess that this is not as great an indicator as I expected.

All in all I think that I went about this repair the right way. I checked everything out to make sure that the $200 worth of accumulators was worth installing. I would say that if I had to replace struts I would probably go with that shock and spring system at Home Page. I am also going to never load up my car that much. A trailer rental from Uhaul is too cheap and convenient to put the extra load on the old car.
 
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