Wagon rear susp air cells - PeachParts Mercedes-Benz Forum

haasman · #1 09-28-2002, 04:44 PM

I have search through the postings but .... how does one know the air cells are bad. I have a '95 wagon, the rear shocks have been replaced, but I still feel the ride quality isn't where it should be.

Additionally, where are the cells located in relation to the rear shocks?

Thanks in advance

Michael · #2 09-28-2002, 07:14 PM

One way to see the cells is to get the car on a lift & trace the hydraulic lines - the spheres themselves are inside the car, though, so all you'll do is locate their hydro connection points. Inside the car, you'll need to remove the panel between the folding, rearmost seat back, and the back seat (middle row). With that panel removed, the spheres are right there (I replaced mine about a month ago). Essentially, the cells are inline with the shocks, but more inboard/towards the center of the car.

If your car is bouncy or abrupt in dealing with bumps, it's cell time. Mine rides like a new car now, and I'm still on my original shocks (184k miles)!

haasman · #3 09-29-2002, 02:12 AM

Is there a standard way to say: Those air cells are bad ....?

Mick J · #4 09-29-2002, 03:55 AM

Yes, the ride becomes very harsh, to point of being almost painful each time you go over a bump. After the bump there is rapid, violent bouncing, not the slow wallowing you get with failed shocks on a normal set-up. Also, if you push down on the rear corner, like a standard shock absorber test, you will find it very hard.

At the time they fail, the level of hydraulic fluid drops dramatically and you may see air bubbles, or a 'froth' in it.

They are underneath the section of floor just behind the back seats (middle row if yours is a 7 seater) as Michael says. Just remove the four screws (can't remember if there are 4 or 6 and its too early to go out and have a look!)

haasman · #5 09-29-2002, 02:32 PM

Thanks Mick.

Are you saying by visuall inspecting them will tell me if they are bad as well?

Michael · #6 09-29-2002, 02:44 PM

Visual inspection will not help you - they don't leak externally

Mick J · #7 10-01-2002, 02:45 PM

No visual way of checking. Inside the sphere is a rubber diaphragm. Air (nitrogen gas?) is trapped above the diaphragm under pressure and the hydraulic acts on the underside of the diaphragm. This aborbs the fluid displaced when the suspension moves and the damper telescopes.

Most cars with conventional suspension have this diaphragm/air assembly inside the shock (hence the term 'gas filled') but for self levelling to work it needs to vary the volume of fluid in the system.

haasman · #8 10-01-2002, 09:05 PM

These replies are helpful and informative.

My complaint is in the rear of our wagon, even though the rear shocks have been replaced in the last 10k miles, it is still a bit floating and not as tight as the front.

I do have Bilstein HDs in the front. I was led to believe that the two were very compatible. Am I wrong?

#9 10-11-2003, 08:22 PM

Is it possible to determine whether a cell/sphere is bad by, having removed it, push something blunt into the 17mm banjo connection. I'd of thought that a good cell would provide high resistance due to the nitrogen pressurization whereas a bad cell will show movement. I just obtained two replacement/used spheres - one sppears bad and the other good - by the above test.

I'm just not sure whether it's a valid test. I've never had the car running correctly to know what good or bad suspension feels like - however, it did seem too jumpy and I've a leaking shock so intended to replace/test spheres.

Steve

psfred · #10 10-11-2003, 09:47 PM

Easy way to check the rear accumulators is to put a foot or knee on the rear bumper and bounce the car. If only the tires bulge, no wheel movement they are DEAD. If very stiff (stiffer than the front), they are going.

Not too bad to replace once you get the panel out, it's usually stuck on the front edge. You will need to get the rear jacked up off the wheels as the rear end will drop considerably when you remove the lines otherwise.

Get a quart of hydraulic suspension fluid, too, you will lose almost that much. Be prepared for it to drip out of everything. Line connections for accumulator are under the car, accumlators inside (why?????).

The struts almost never leak unless driven for quite a while on bad accumulators -- the overpressure blows the seals out. They are a bit dear....

Peter

haasman · #11 10-12-2003, 12:39 AM

Peter

Thanks again for your experience and advice.

Haasman

d2bernhard · #12 10-13-2003, 06:51 PM

Difficult? Not really. Dirty? Yes. Some very cramped spaces? Yes. See my post -- perhaps search on hair and gojo. Improvement? Wow! My W124 '92 TE is so lovely now. Go ahead and change your fluid while you are at it. I didn't, and wish I had. Almost half comes out to do the job anyway.

d2bernhard · #13 10-19-2003, 12:47 AM

I just read through this again. Loose and floaty sounds more like your multilimk setup than the air cells -- all the bushings and comtrol arms back there..

#14 10-19-2003, 04:49 AM

Well my 300td/1983 would have passed the 'bounce it and see one return' test but when driving the ride seemed underdamped. I also had a bad rattle from one side/rear and a leaking shock absorber. I removed both spheres - one was full of fluid - broken seal. One worn plastic link between anti-roll bar and suspension arm was the cause of the noise. So, it's still not clear to me how to test spheres with the eloborate pressure gages & valves described in the manual. Whilst removal and inspection can detect broken sphere it can't detect spheres that are partially 'shagged'!

Steve

#15 10-19-2003, 03:17 PM

Re-reading my post above - instead of saying

'So, it's still not clear to me how to test spheres with the eloborate pressure gages & valves described in the manual. '

I meant to say ...

So, it's still not clear to me how to test spheres withOUT the eloborate pressure gages & valves described in the manual.

Sorry 'bout that.

Steve