conecaster

I am wondering if any one here has ever replaced the accumulators on the rear suspension of an e320 wagon?

I found the parts online for $99 each. I understand the hydrolic fluid needs replacing? I have no idea how that is done?

Are there critical issues that must be paid special attention to in doing this task?

The garage wanted 6 hours labor and $300 each for the parts. I'm presumming this job is not terribly difficult, any advice would be most appreciated.

Thank you,

P

steve211

Do it yourself and save!
If your at all handy, it's easy. I'm no certified mechanic, but I did it in way less than 6 hours, coffee to beer. Only parts are the two accumulators and hydraulic fluid.

Get some brake line wrenches and penetrating fluid (soak the lines to be removed the night before). That and a pair of ramps (great....but not required) and basic hand tools is all you need.
A I remember, relieve system pressure via the bleed valve, loosen the hydraulic line going into each accumulator, then lift the carpeted metal cover from the interior and remove the three retaining nuts that secure the accumulators and replace. Once all is bolted back in, top off the resevoir, fire up the engine and bleed the system via the bleed valve.

Steve
Columbia, SC

myfirstbenz

It is DIY but make sure not to round off the fittings because they tend to get seized so use some good penetrating oil like PB blaster.

It is a messy job, and one that does take some time, but it can be done. I get my parts at wholesale www.mercedessource.com Their prices are the best you will find, even better than my "at cost" prices when I knew a guy who owned a shop. Call Kaia and she will hook you up for all your parts needs. They also sell manuals and trouble shooting guides, they are good people.

White_Knuckles

I've got a 95 wagon and wondered what you're solving for? No auto-leveling or ride quality? Lame question but how do you suspect the accumulators are failing?

Stupid widgets... and SO many!

conecaster

Thank you for your responses, very helpful.

I don't mean to sound ignorant, But I do not understand the SLS.

How do replace the hydraulic fluid? what does the accumulator do.

Why do you start the car to bleed the system? Is the hydrolic fluid the leveling and the shocks air devices or is it the other way around?

I have a bit of experience working on cars but I like to understand the technology before plunging in. I get the impression you guys have a deeper understanding of the SLS system than I do. I got just a little lost trying to understand how the accumulators and shocks work together. It was my understanding that accumulators, although called air cells air actually nitrogen filled to better deal with pressure at various temperatures. So why are the hydrolics involved?

Thanks in advance,

P

BTW- the car was diagnosed by a certified M-B garage.

steve211

Not sure how clear I can make it but here are the basics.

A damper (shock/strut) will reduce oscillations of the unsprung mass (that not suspended by the springs...like wheel/tire suspension etc), and thus provide an even ride and a keep the tire on the ground where it can provide traction for braking, turning and/or acceleration.

This, in a basic sense, is done when the energy of the moving mass, displaces the hydraulic fluid within the damper.

The SLS takes it a step further and has the damper units also assist in providing the ride height (level) as well, by increasing or decreasing the amount of hydraulic fluid within the unit. The system pressure, provided from the pump, forces fluid into/out of the dampers via a level switch.

The accumulators are essentially remote reservoirs that have on one side, high pressure nitrogen gas, and the other side is the hydraulic system fluid, separated by a rubber (presumably) diaphragm.

Now when the energy from the wheel/tire and other unsprung mass, forces the damper unit to compress, it forces hydraulic fluid out of the unit (since it is non-compressible) and into the accumulators where, on the other side of the diaphragm, is a compressible fluid. The nitrogen compresses and absorbs the energy of the displaced fluid. Once the opposing forces equalize, the stored energy from the now compressed nitrogen gas pushes on the diaphragm, sending the fluid back into the damper unit, which returns the wheel/tire back to the ground.

When the accumulators lose the nitrogen pressure (due to diaphragm leakage into the system) the displaced fluid just gets sloshed back and forth until the energy is dissipated. Meanwhile, the driver feels the rear end bouncing up and down, and up and down and up and down. It looks and feels absolutely ridiculous and makes not for the safest way around a corner.

Anyway, hope that helped a bit more than it confused. =)

Steve
Columbia, SC

steve211

Almost forgot....When I replaced the fluid, I just siphoned the fluid from the reservoir in the engine compartment with a turkey baster and replaced with fresh. Then topping off as needed after the job while opening the bleed valve with the engine running. Similar to bleeding brakes, but the pump does not need any voice commands to provide constant pressure. =)

conecaster

an absolutely beautiful description steve.



So, there are just a few holes left in my knowledge if you do not mind more simple questions,

first, if the accumulators are the over flow it would appear they would need bleeding correct?, is this where you bleed off from? Part of my confusion was not understanding how the fluid is replaced and properly bled. So, you fill the system at the pump which is located under the hood and operated from a pulley?

Fluid can be pumped right through the system from the reservoir on the pump?


The thing sounds like a very simple repair.

the garage said that it took a long time to do because the passenger side accumulator is a real bear to get to, this sounds like non-sense to me.

I did not notice you mentioning any issue with one side being any harder to access than the other?

My last curiosity is what kind of hydrolic fluid does it require?

I really appreciate the great advice.

P

steve211

I would not think of the accumulators as overflow really. This is the same basic function as a typical gas shock....just that....on the SLS units the gas that is compressed is externally located. Presumably due to the fact that with the additional fluid required to control the load level....there simply isn't enough room in the damper body.

The passenger side is a bit more difficult because there is the level control valve and it's a bit tighter access. The drivers side is absolute cake.

I did not take the time to determine if there is an acceptable substitute so I used the MB fluid.

Yes, you fill the reservoir under the hood. Don't run the pump dry....just siphon and replace. Then use the bleed screw on the level valve and let the pump force the fluid and after repair air out. It's at a very high point and under considerable pressure.
The pump is a tandem type that is not accessory belt driven but rather is driven off the crankshaft and provides pressure for the SLS and the power steering.....again in tandem as these are separate systems with separate reservoirs.

Oh...and they each have filters to remove suspended solids. P/S is paper while the SLS filter is a serviceable metal screen. But honestly it's cheap enough ($7.90 at AZ autohaus) that it was not worth cleaning the nasty original in my car. IMO

Now that you have a better understanding....it's time to crawl under there and survey the situation. That usually helps me glue it all together in my head.

Steve

White_Knuckles

Nice details Steve. It is tough to describe this system. Thanks to your input I have a much better understanding. SLS and shock dampening are handled by the same system. I made it harder.

The piping from that control unit under the hood looks scary. Hate to break that baby!

steve211

Had this question via PM but thought I'd share it in this thread just in case someone else ever had a similar question.

<<Steve
I have a 02 E320 wagon with the self leveling. I was reading a thread you posted on the subject of bad accumulators. I believe that is what is wrong with mine. On the 02 they are very easy to get to without any problems. My question is, Where is the leveling valve located? Also what is the procedure for bleeding it? Suspension under pressure, not under pressure, etc.

Thanks
Skip>>

Hey Skip,

The leveling valve:
On my 1994 wagon the leveling valve was mounted underneath the car via bracket to the rear swaybar. It may be slightly different on the 2002 but if you follow the lines to the accumulators they will come from this valve. the bleed screw should be on top of the valve which looks much the same as the bleed screws used on brake calipers.

To bleed:
you need the car running and weight on the suspension BUT you MUST have the wheels on a pair of ramps or you can be crushed! You could find a way to improvise (back up onto a curb etc) but the key is IF the Self Leveling System (SLS) were to fully collapse, you would still have enough room for your body underneath.

So while it's backed onto ramps, start the engine and open/close the bleed valve to purge the system of air. The rear ride height may oscillate a bit until most of the air is purged. Don't have your face directly underneath the valve or you will eat mess of foamy hyd fluid. You will hear the amount of air released decrease each time you bleed and let system pressure build again.

Dont forget to have enough fluid in the reservoir. If the hyd fluid level in the reservoir gets to close to the pump inlet, it will draw in air and you will have to start over.

Hope this helps!

Steve Hauptmann

e350forme

getting ready for this job. My ride is silly bouncy and hopefully nothing else broke. I plan to disconnect the accumulators one at a time and then bleed the system. i wont mess with the up down valve . hopefully I can get air out .

ds190

I rec you bleed it per factory procedure. There will be air trapped in the rear circuit when you replace each accumulator.

http://www.w124-zone.com/downloads/M...is/32-0620.pdf

http://www.w124-zone.com/downloads/M...is/32-0630.pdf

e350forme

thanks for the bleeding document. Its a bit dense for me to understand, will try and re read it a few times . thanks again

steve's post helps quite a bit (dumbs it down from german-ese)

e350forme

all fluid bled and went as planned. thank you for help.