E320 Wagon - rear bushings, which ones?
 

I suppose its a semi common problem for these wagons to have a rattle/clunk/thump noises coming from the rear. I've looked and looked and cant find anything obviously wrong, but every time I go over a speed bump, *CLUNK CLUNK*. I guess by process of elimination its gotta be some kinda bushing. I've read a lot of threads regarding rear stunt mount bushings, and apparently they come in 2 pieces? Well when I look at FastLane I find THIS.

The first item is listed as a "Rear strut bushing." Its not a 2-piece affair. I guess this is the part that could be acting up? is there a way to test the integrity of the rear strut bushing?

what about rear control arm bushings. apparently there are inner and outer versions. can these be tested to see if they are guilty of the horrible noise? if so how?

What year and how many miles?

oh sorry. its a 95 with 116k

Your car has the self leveling hydraulic rear suspension. The symptoms you describe (speed bump clunk) could also be caused by failed accumulators. Do some searching with the following terms: nitrogen chamber, accumulator, rear suspension.....

from your description it sounds like the rear subframe bushings.there are four, two of one style at front of subframe and two of another at rear.

I've got new accumulators. thanks though.

ah okay. I'm gonna go jack up the car and visually inspect them right now. Fastlane has a bunch of subframe mount stuff but most posts here referred to shock-mounts. I dont know what else it could be. I'm running out of components to check!

so looking for an obvious issue with the rear sub frame mounts proved uninformative. Is there any way to test or otherwise diagnose that they aren't doing their job? hammers, screwdrivers, removing the bolt?

Unless they are really shot, it might not be visable. The rubber bushing comes loose from the center steel bushing and allows the subframe to move up and down. Working a big screwdriver or pry bar between the washer under the head of the bolt and the subframe might reveal some movement of the subframe. On my old '87 300TD it was obvious, the tech caught during state safety inspection. I suggest removing only 1 bolt at a time.

Here's some reading for you

DIY Links by Parts Category / Suspension
http://www.peachparts.com/shopforum/diy-links-parts-category/142397-suspension.html

Bob

More Questions
 

So I went to the shop today to ask pretty much what I ask you guys. its a pretty good place thats done good work for me in the past. Anywho he said the problem was most likely in the rear shock mounts. I ask about the sub frame mounts and he said usually not. granted we didn't get the car on the lift to really check it out. also I had my dad sit in the back while I went over some speed bumps, thats when the noise is most obvious, and he had his fingers on the nut of the shocks (I took off the panel that covers the accumulators and shock mounts) and he said he very clearly felt the "thunk" transmitted there. The shop guy (who happens to be the owner) said that the mounts for the hydo shocks aren't available and that you had to buy a whole new one.

Looking at fast lane I don't see a separate category for rear shock mounts, but looking at this picture, you can clearly see its not an integrated part and thus should be very easily replaceable. Is it? can the mount be had without buying a whole new shock?


http://img.eautopartscatalog.com/live/L400024750SAC.JPG



Also, to clear something up in my head the subframe mounts we have been talking about are the bushings that go between the rear subframe the body of the car correct? not those large black bushings that are on either side of the differential where the control arms connect? Anyway those 1) could create the sound I have described and 2) are easily replaced with out specialty tools?

I entered the VIN from my 94 e320 Wagon into EPCnet [used by MB dealers] and found the attached parts and piks.
Hope it helps
Bob

Awesome, thanks, I'm calling the dealer now!

EDIT: BTW, how does somebody get access to those picts and part numbers?

EPCnet is provide thru MB. Subscribe monthly or yearly. I did yr @ $24. It uses "java script" so that application must be on your computer.

Go here for info
http://epc.startekinfo.com/epc/

Bob
PS Although Startek does not gurantee operation on Mac OS, mine works on my G4 [mfg 2001] running OS 10.3.9. However, the "F" keyboard functions don't work, so I use the mouse.

FYI

After servicing several of these wagons....I find the quietest ride is attained by setting the rear suspension as follows :

With vehicle on a drive on four post lift and with the engine running.....slacken off the roll bar clamps so the rod /clamp assembly is loose.

Run the hydraulics through full lift to minimum lift a few times and make an indicator rod to measure maximum and minimum height.

Set the suspension so it settles in the middle of the two with adjustments to the clamp.

The ROAD SPRINGS should be carrying the weight of the car, NOT the ram shocks....if too much pressure is supplied to the rams by the ride height valve the suspension will THUMP.

If you are able to use a pressure gauge to read ram pressures the empty load pressure should be under 100 psi.....any more indicates the rams are carrying weight.

If carrying a load, the 'thump' is to be expected, but in factory trim the shocks are not supposed to carry any load.

If the rear sits low, the springs are weak. ...DO NOT try to adjust ride height with the hydraulic ride height valve.

Buy new springs.......

If you get bump thump after adjusting this way, remove the lower ram mountings on both sides and record the ride height at the forward splash rubber lip to the ground or other chassis part.....refit the shocks and adjust ride height with the roll bar clamp to your recorded measurement.

BTW...Continuous high ram hydraulic pressures will make the shocks weep.
If you feel the upper shock mounts are not cushioning the ride properly or do not compress correctly you can obtain similar shock bushes made of Urethane from after market parts places and make your own.

The accumulators will fail after approximately 6 years...that is the nitrogen will eventually seep through the rubber diaphragm inside the sphere and there will be no more reserve fluid to dampen shock movement.

The spheres are initially pressurized with nitrogen to approx' 2300 psi.....do not incinerate them or cut them open.