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  #1  
Old 03-04-2004, 03:48 PM
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Leveling sustem question

I am in the process of changing the line from the supply tank to the leveling system pump on my 85 300TD (line was "weeping", appears to be the original line). Tank was dirty inside, removed and cleaned out residue. Now, when I refill the tank, can I just attach a hose to the small return line to the tank, start the engine and flush out the old oil in the system? I read somewhere on this forum that they cracked the bleed valve on the controller in the rear to bleed the system. My system works just fine, no leaks (except for the supply line to the pump) so can I flush it as stated above?
Thanks
Jerry
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1971 108 280SE 2.8 "Ronnie"
1985 300TDT (76,904 Original miles ) "Sadie" (Sold-went back to Arkansas)
1984 300DT "Green-go" (Sold)
1984 300DT "Silver Bullet" (Sold)
1956 220S Ponton
1985 300DT
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  #2  
Old 03-04-2004, 04:00 PM
lrg lrg is offline
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I've never tried that and I'm not sure it will work. As I understand the system, the return line will only get flow when the valve in the rear releases an overpressure situation (like when you remove a heavy load after the rear has pumped itself up). I think you'll still need to bleed from the rear valve bleed nipple. This must be done with the engine running and be sure you have the car on ramps as the rear can drop a few inches when you release the pressure. You should also replace the filter if you haven't already. It's in the top of the tank and filters the return fluid. If you do try to bleed it your way and it works, be sure to replace the filter AFTER you are done. Let us know how it goes.
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  #3  
Old 03-04-2004, 04:32 PM
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lrg,
Thanks, I will try it that way and will post back results.

Why wait to change the filter after bleeding? If the system works as I think it does, removing the return line and allowing the old fluid to flow into a container would not allow old fluid to return to the tank, right? Please correct me if that assumption is wrong.
Thanks
Jerry
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If you don't learn something new every day, you aren't paying attention!!
1971 108 280SE 2.8 "Ronnie"
1985 300TDT (76,904 Original miles ) "Sadie" (Sold-went back to Arkansas)
1984 300DT "Green-go" (Sold)
1984 300DT "Silver Bullet" (Sold)
1956 220S Ponton
1985 300DT
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  #4  
Old 03-04-2004, 04:51 PM
lrg lrg is offline
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Jerry,
You're right. I was thinking you'd flow it through the filter but obviously if you remove the line before the filter it won't matter. Either way, it's a good idea to replace the filter.
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1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold
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  #5  
Old 03-05-2004, 03:07 PM
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lrg,
Thanks for the suggestion re changing the filter, will do when the system goes back together.
Jerry
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If you don't learn something new every day, you aren't paying attention!!
1971 108 280SE 2.8 "Ronnie"
1985 300TDT (76,904 Original miles ) "Sadie" (Sold-went back to Arkansas)
1984 300DT "Green-go" (Sold)
1984 300DT "Silver Bullet" (Sold)
1956 220S Ponton
1985 300DT
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  #6  
Old 03-05-2004, 05:50 PM
R Leo's Avatar
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When I changed the accumulators on my wagon I changed the fluid and filter too.

To remove the fluid from the reservior, I disconnected the linakge from the positioning valve, moved the valve arm to the "lift" position, connected a piece of tubing to the bleeder on the positioning valve (palcing the other end of the tube in a container that could hold all the fluid) then opened the bleeder.

Next, I started the engine and let the engine pump all of the old oil from the reservoir, through the valve and out into my waste oil container.

When the reservoir was almost empty, I poured approximately 1/2 litre of new fluid into the reservoir and let the engine run until clear (relatively clear, that is) fluid was being expelled out of the bleeder.

I killed the engine and closed the system; replaced the SLS (self-leveling suspension) filter (that's interesting to do) and replaced the accumulators; filled the reservoir to the mark with MBZ/Meyle hydraulic fluid and cranked her up.

I let the car run for several minutes to bleed the system and added a little fluid. Then, I drove around a bit and checked the fluid again. Needed about an additional pint.

That's been a month ago and the ride is soooo great now, I've been kicking myself for at least three of those four weeks about not having done this a year ago.
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  #7  
Old 03-08-2004, 05:04 PM
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R Leo
Thanks for the info re bleeding the system. I had to wait until today to get the filter and I will do the system tonight.
Thanks again!
Jerry
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If you don't learn something new every day, you aren't paying attention!!
1971 108 280SE 2.8 "Ronnie"
1985 300TDT (76,904 Original miles ) "Sadie" (Sold-went back to Arkansas)
1984 300DT "Green-go" (Sold)
1984 300DT "Silver Bullet" (Sold)
1956 220S Ponton
1985 300DT
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  #8  
Old 03-17-2004, 05:13 PM
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Randy,
Did your bleed suggestion, worked well. When I opened the bleeder valve, at first just air and small amount of fluid came out. Let system continue to bleed and after about two minutes, clear fluid started coming out, let it continue to run a bit longer, closed up bleeder, refilled reservoir and all is well! Thanks to all for suggestions!
Jerry
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Jerry -
If you don't learn something new every day, you aren't paying attention!!
1971 108 280SE 2.8 "Ronnie"
1985 300TDT (76,904 Original miles ) "Sadie" (Sold-went back to Arkansas)
1984 300DT "Green-go" (Sold)
1984 300DT "Silver Bullet" (Sold)
1956 220S Ponton
1985 300DT
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  #9  
Old 03-17-2004, 10:27 PM
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R Leo...

Were your accumulators shot, or did you just replace them because they were aging? I've been told that unless they're completely shot I'd never notice the difference between old and new ones.

I don't know if my fluid or filter has been changed in many years... And I don't know if my accumulators are original or not, but they must be ancient regardless. Something in my SLS is leaking (hopefully not the shock itself, eek.. $$$$) so I'm planning on examining the system closely soon and doing what I can for it. Would it be worth replacing the accumulators while I'm at it?
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  #10  
Old 03-18-2004, 03:18 AM
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Offhand, I don't know if there is a testing procedure for determining the condition of the accumulators. From my recent experience, I would say if your accumulators are more than 10 years old, replace them.

I based the decision to replace mine on the following:

1) The ride was harsh. You could feel every expansion joint and bump in the road. Even minor bumps in the road would literally move you up and down in the seat.

2) The ride quality of my wagon was SIGNIFICANTLY different from the W123 sedan that also I own. Somehow, it seemed to me that the engineers at Mercedes-Benz™ would not permit this sort of difference.

From those two conditions, plus an understanding of the way the rear suspension works in these cars, I deduced that collpased accumulators (no gas space left in the bad accumulators would allow no additional springing by compressing the gas) would be the most likely cause of the harsh ride.

It was an educated guess that turned out right.

Some other hydropneumatic suspension scenarios:
An excessively springy (no damping) ride would be indicative of bad struts or no fluid in the system (a leak).

Failure for the SLS to maintain proper ride height would be: 1) no fluid in system, 2) failed or sticking position sensing valve, 3) broken or loose linkage from sway bar to position valve, 4) broken sway bar links at wheel, 5) failed SLS pump.

Based on the above, you'll see that it's really pretty simple to diagnose these systems. IMO, and considering what they do, they have to be one of the most trouble-free systems on the car and well worth putting money into for a proper repair.
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Last edited by R Leo; 03-18-2004 at 04:43 AM.
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  #11  
Old 03-18-2004, 04:30 AM
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The system is self- bleeding. Change the top shock bushings,2 per side, and it will ride like new.

John
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  #12  
Old 11-08-2007, 06:16 AM
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this question may have been asked in the past , but here goes anyway.......what exactly fails in the accumulators? is it the diaphragm ? does the nitrogen charge leak out? has anybody attempted repairing them? aircraft hydraulic accumulators are similar in function with the advantage of having schrader valves which allow for topping up the nitrogen from time to time . on aircraft they sit around 1500 psi and have a separator piston with "o" ring and two teflon back -up rings separating the gas from the fluid could this be a replacement solution?
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  #13  
Old 11-08-2007, 06:32 AM
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There is a rubber that separates the nitrogen from the fluid. Once that diaphragm is broken, usually from fatigue or breakdown of the rubber from infrequent oil changes, the nitrogen is gone forever and the accumulator will have to be replaced.

Something like this:
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  #14  
Old 11-08-2007, 09:02 AM
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A few years ago, someone familiar with Citroens which use a similar system said that the accumulators could be rebuilt since Citroen accumulators were rebuilt. By rebuilt I think he meant recharged with nitrogen. I don't think a source for the rebuilding was ever posted.
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1985 409d 65k--sold 06
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  #15  
Old 11-08-2007, 02:43 PM
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Although similar in function, the Citroen accumulators are mechanically different. Whereas the Benz units are crimped together, the Citroen spheres screw together and can be taken apart.

Here's a nice writeup on that system:

http://www.actwin.com/toaph/citroen/work/work.html
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