Strange ride on 300td - new shocks?

Recently my '81 300td started behaving strangely - sort of "porpoising" when encountering bumpy or wavy roads almost a frequency type of thing
that starts the car rocking. I have to slow down or speed up to get it to stop. Not dangerous, at least not yet.
It's got 163K on it, and I don't think the front shocks have been changed (wouldn't have any way to know). The rear seems sturdy enough when the car is running, but the front is a little mushy.
It's a definite difference that happened in a relatively short period of time.
Suggestions?
TIA
tweaks
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The shock absorbers aren't dampening anymore. (They're gone basically). This is what a car rides like when it has only springs and no shocks (to dampen the bumps) for suspension.
New shocks are probably in order.
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Change out all the shocks to new Bilsteins.
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Agreed. Use ONLY Bilsteins. They're not cheap but have a lifetime warrenty. Nothing else seem to work properly or last.
Your original shocks did pretty well to last 25 years jah?
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Thanks - that's what I was thinking, but I wanted to see if the self-leveling suspension might be the culprit - it happened pretty quickly.
So the next question is comfort, heavy duty, etc. I don't spend a lot of time on the highway, and our roads are pretty good.
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I have a 1982 300 TDT with the load leveling rear suspension.
Your accumulators have most likely failed. The rear suspension on these vehicles does not have shock absorbers like many cars. You have struts that are regulated by hydraulic fluid that is pumped through the system to keep the vehicle level regardless of load. These struts do not have an air chamber that allows them to absorb shock. The air chamber to absorb shock is found in a different component of the system known as the "accumulator." There is one on each side. They are black metal spheres. There is a rubber diaphragm inside that divides the inside of the sphere in to two chambers. The innermost chamber is filled with a gas, probably nitrogen. The outer chamber is a part of the hydraulic circuit and is filled with hydraulic fluid. When you hit a bump, the rubber diaphragm inside the chamber expands under the increased pressure caused by the axle pushing up suddenly on the strut and absorbs the shock. Eventually those rubber diaphragms break and the entire sphere fills with hydraulic fluid. Since liquids retain their volume, the sphere can no longer absorb shock.
You will notice a small deterioration in your vehicle's ride when one accumulator fails. When the second one goes, your car will start acting like a kangaroo like you describe.
Here is the BenzBin listing for an accumulator
http://mercedes.thebenzbin.com/?year 82&make=MB&imageField22222.x&imageField22222.y
And this guy has them on eBay for about $83 each in pairs.
http://cgi.ebay.com/ebaymotors/MERCEDES-126-MORE-NEW-Rear-Shock-Accumulator-Set_W0QQitemZ110182887940QQihZ001QQcategoryZ42609QQcmdZViewItem
They are not difficult to change out. You don't need to remove anything but the accumulators themselves. It is kind of a messy job because hydraulic fluid tends to ooze or squirt out no matter what you do when you remove them.
Paul

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I've only lusted after, but nevr owned a wagon. Isn't there soem test so you can figure out if it's the rears? Isnt't the back end supposed to maintain a constant ride height no matter how much the car is loaded or something?
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Just push down on the back end. If it does not move, the spheres are blown. When they blow, the back end is rock solid.
wrote:

maintain
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By the way, don't drive the car any more than you have to with the accumulators gone. If you do, it puts extreme pressure on the system every time you hit a bump because there is no air chamber space to absorb the shock. That can blow the seals on the struts, and then you have to replace the struts. They are $368 each.
Paul

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Thanks...
I noticed a loss of hydraulic fluid when I was doing a routine check, so I filled it up. This is what I was worried about because of the dramatic change in the ride.
Is there a means of verifying this is the problem that comes to mind? I'm perfectly able to do the work, but hate to expend the resources for them if it's really not the problem...
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Push down on the rear end. If it rock solid, replace the spheres NOW.

if
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Thanks
Actually, it's still "somewhat" bouncy. The rear end "raises up" when I put the car in reverse (which I queried the group about before and was assured was OK). Sort of settles initially when putting into a forward gear. There doesn't seem to be any difference with the car running or not. That doesn't sound promising.
I think I'll crawl under there tomorrow and see what I can see.
What I'm reading here is:
1. Put it on stands 2. Inspect for oil around the shocks (I've done before, but will do again) 3. Turn on the engine. 4. Check to see if the lever on the valve makes things happen. 5. Remove a line and see if it looks as if sufficient hydraulic fluid is being circulated. 6. Possibly, take the accumulators off and inspect to see if the diaphragm or membrane is still intact and resilient.
Does that sound about right?
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The spheres are sealed balls..... you will not see anything.
With the car off. Push down on the front. Car goes down and comes up, right? Push down on the back. Should be as easy as the front. Is it hard as a rock??

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It's the accumulators. Almost definitely. Shocks don't go out the fast but the accumulators do. And the result is what you describe. I have a 1982 300TDT too. Replace them and you will ride like new.
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Thanks
Definitely not as easy as the front. A small amount of give, so I'm thinking the accumulators have gone.
I read something about the "wrong" kind of hydraulic fluid? Is it a MBZ specific fluid that I should use to replace once the whole thing is done?
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I just spent an hour underneath - I don't really "feel" much difference than has always been there. The front moves more than the rear, but the rear is still "spongy" - not rock hard.
There is no evidence of oil or leakage anywhere along the rear struts, nor anywhere else in the rear leveling system assembly. Didn't see any movement in the sway bar, though.
In the engine compartment, the hydraulic fluid comes out slowly but steadily from the filter into the reservoir. I didn't think that it would come out with much force, so that seems OK.
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if
hi just did the rear suspension on my 230te, nothing much to it, bit fiddly and a bit messy as mentioned but easy enough. Just try bouncing the rear end, if the spheres are gone the will be no movement. If you lost the fluid its probably inside the spheres where the gas was, hence hydraulic lock. BE VERY CAREFUL WITH THE VALVE BODY - its ally, soft and expensive. The spheres are actually inside the car under floor at the back, access panel under the carpet hth cheers! balge
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I'll keep ya posted.
Thanks for all of the information and advice, as always.
tweaks
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