Accumulators, Rear Suspension, the whole nine yard - PeachParts Mercedes-Benz Forum

pilot2000 · #1 10-11-2006, 05:13 PM

I hope I can find someone that can help me here, b/c I really don’t feel like spending $2885+ on this.

My 99 S500 road a bit rough and bouncy, I replaced the Accumulators
Still rides rough for an S500, took it to the dealer to diagnose they said I need new Accumulators, even though I had just replaced them 2 weeks ago, and new shocks at $800 each.

Now when I did the Accums I lifted the car on a lifts but not on ramps so there was no pressure what-so-ever on the suspension, I bleeded the system, took the old accums out and fitted the new ones. The system did not drain any fluid, even though the reservoir had lot enough in it. After replacing the accumes the car is a slightly higher then before, more like normal height now, but still rides rough.

Q1 is what did I do wrong?
Q2 is How can I properly bleed the system to make sure I get all the air out?
Q3 is Can the Accumes go bad that fast?

HELP!

Thank You very much in advance

Gilly · #2 10-11-2006, 06:39 PM

Q1; nothing, other than replace the wrong parts. They should have been tested before replacing, so maybe that's the actual answer to Q1, you didn't test the system. The tools to do this don't grow on trees though, so I'd go easy on yourself, you replaced the most COMMON part to fail.
Q2; There is no bleeding procedure, the system self-bleeds, the fluid just normally circulates and will take any air in the system back to the reservoir.
Q3; Um, sure, I guess so, BUT I wouldn't allow them to replace them as I am sure they are OK, I mean if you put MB accumulators on them? It doesn't say "Acme Accumulators" on them? You didn't buy them on a street corner from some shifty guy in a greasey trenchcoat? Their not "used" accumulators you picked up at a swap meet? Bought 'em at NAPA or Autozone? Nahhhhh, you didn't. They're fine. I suspect the scenario is this; You replaced the accumulators. Didn't fix the rough ride. Took it to the shop and had em check it and probably told "someone" that the accumulators didn't fix it. Tech says "well, if it's not the accumulators then it's the shocks" and had them BOTH looked up, forgetting that you said the accumulators were replaced.
Just for reference, bad accumulators will primarily just make a knocking noise, usually the ride quality is fine. Unless they tested the accumulators and KNOW they are bad, I'd turn down that part of the job. If you can do the accumulators yourself, are you sure you can't do the shocks too?
Gilly

pilot2000 · #3 10-11-2006, 06:52 PM

I can certainly do the shocks as well, I can do just about any replace on the car, since my 93 is the same body I am pretty familiar with those now, but I don't want to go mad replacing stuff. And since the dealer said that the accumes needed to be replaced and I know I just did, I am not trusting what they say, but I guess I have no choice, I can't see at this stage anything else that can make the car ride rough. So I will do them and see what happens, at 130K it is not a bad idea anyway.

Thanks again.

pcmaher · #4 10-12-2006, 08:30 AM

Bad accumulators usually do cause a very stiff ride due to the fact that the nitrogen gas has leaked out and is replaced by hydraulic fluid. Please read my write-up before you buy expensive parts that may not be needed...

http://v12uberalles.com/pressure_spheres.htm

Gilly · #5 10-12-2006, 08:40 AM

I liked the write-up. There's not alot of things that are going to affect the ride quality in this system, the shocks and to a lesser extent the accumulators. If the accumulators fail, there is nothing to take out the hydraulic "shocking" when hitting bumps. The ride will be substantially the same, but you will get a bad knocking noise when hitting bumps. This is BAD for the shocks so you don't want this to go unattended for very long.
You can "bleed" the system by raising and lowering the car with the level valve if you like playing with the levelling valve and making the car go up and down (if you have a good pump it will raise and lower actually pretty fast) but this isn't needed, the system will circulate the air out of there by itself. If there IS any air in the system, one would think it would provide a "spongy" ride not a harsh ride anyways.
Gilly

mbdoc · #6 10-12-2006, 09:25 AM

"most of the time" MB leveling system components fail due to constant operation. The design is to work only when loaded. REAR spring sag makes the system operational MOST of the time. That causes accumulator failure..if the accumulators aren't replaced as soon as they fail then the shocks have equal pressure on BOTH sides of the damping piston & that causes premature shock failure.

When the accumulators are replaced check the ride height with the leveling system OFF.. the rear of the car should still be at the correct ride height..if not then install thicker spring pads OR new springs.

Even on a 6-7 year old car the shocks will fail if the accumulators are bad long enough & car is driven where the shocks are being damaged.

pcmaher · #7 10-12-2006, 12:34 PM

That's good info M.B. DOC. It makes sense that the springs should maintain correct height in an unloaded condition. I will need to modify my write-up. Thanks.

psfred · #8 10-12-2006, 08:30 PM

On the assumption that this system is very similar to the one in the 88 TE, bad accumlators will eventually lock the suspension completely -- once the nitrogen is so low in them that the diaphram cannot move, they are full of incompressible hydraulic fluid and the strut piston cannot move at all. The only "spring" left in the rear suspension is the tire on each side. The car will bounce off the pavement in this condition, and follow road surface deviations VERY closesly. Unmistakeable.

Driving it in this condition will blow the seals out of the struts fairly quickly, causing them to leak badly.

A rough ride with good accumulators could only be the struts binding or some pivot in the suspension either sticking or loose.

If this has the typical later model multi-link rear suspension, it's time for new links, the rubber bushings are shot and the torque link is banging on the subframe mount under the rear seat. Very harsh, very loud, and will cause "squirrely" rear end movement and torque steer (pulls one way under acceleration, the other on trailing throttle). Thrust links usually just squeak, they don't knock unless really bad.

Take a peek at the links -- if the center sleeve isn't centered, or there are any signs of shreds of rubber, replace them.

Peter

pilot2000 · #9 10-13-2006, 03:42 AM

I took a good look around and all bushings and links seem to be in good shape, the struts do exhibit a sign of little leaking, I did ride on bad accumes for about 6 months though, because I thought my 18" wheels were causing it and the damn constant construction on Chicago roads that never let up. I am not certain but positive the shocks need replacing as well. I have to bite the bullet and do it, or it will be an S500 that rides like a rough pickup truck, no offense to pickup trucks guys

I did find the Sachs rear struts for about $550 each and I am doing the front ones as well for about $100 each, as might as well since I am doing this. I replaced the front sway bar links when I got the car and all the bushings and links all the way round seem fine. So this will take care of the suspension for a while to come.

After that all is done, I need to work on resealing my gearbox, these cars are known for leaky gear boxes, both of mine have that problem. Any good links would also be very much appreciated.

Thanks for everyone’s help and input.

Thanks pcmaher for the link, that was excellent

AtlBenz · #10 11-15-2006, 08:58 PM

Quote:

Originally Posted by psfred

On the assumption that this system is very similar to the one in the 88 TE, bad accumlators will eventually lock the suspension completely -- once the nitrogen is so low in them that the diaphram cannot move, they are full of incompressible hydraulic fluid and the strut piston cannot move at all. The only "spring" left in the rear suspension is the tire on each side. The car will bounce off the pavement in this condition, and follow road surface deviations VERY closesly. Unmistakeable.

Driving it in this condition will blow the seals out of the struts fairly quickly, causing them to leak badly.

Peter

wow. i've got a 95 e320 wagon, and the car bounces around like crazy in the back. the shocks look fine (ie. no leaks so far) but now I am paranoid and want to go look again. would the be best course of action be to replace the accumulators ASAP? how will i know if there is other damage? do I just put in new accumulators and hope for the best? any conclusive way to KNOW the accumulators are shot aside from "bouncing around like crazy?"

whats the procedure for changing them out, is it super straight forward (ie. once i expose them it'll be painfully obvious)?

sorry for the barrage of questions, but now I'm really freaking out.

Rusty Boltz · #11 11-15-2006, 10:07 PM

Just replaced accumulators im my 91 300 TE wagon on Monday. Now ride is beautiful. Before that it bounced badly and would make daughter car sick after just a few blocks. I let the dealership do it cause I thought the parts were about $100 each and I had been doing other car work all weekend. Besides the $198 cost each for the parts I am otherwise very happy.

The wagon rode badly with more than one occupant. Now I can cary 5 adults and no bounce at all. I do wish I had waited and done the work muyself next weekend because I spent $695 and probably could have gotten by with parts plus 3-4 hours work.