94 E320 Wagon thumping rear suspension - PeachParts Mercedes-Benz Forum

jcwells · #1 11-01-2006, 03:22 PM

I just finished some extensive work on this car:
Rust repair
New windshield
Head Gasket
Engine harness
O2 sensor
Cat back exhaust system
Throttle actuator rebuilt
New rear hydraulic accumulators and associated plumbing due to corrosion
New blower motor
New alternator
Rear calliper rebuild
Fuel pump
As well as other more routine items.

And, although I replaced the rear accumulators the thumping that I thought was accumulator related is still there. It is like every bump and ridge in the road is being transferred into the rear cargo area of the car. I have had the car on the hoist any number of times (a luxury I have in my garage) but cannot see any worn parts, nor can any of the various suspension elements be manually moved. That doesn’t surprise me though since a hanging suspension would likely be under some tension and arm strength may be unlikely to induce the problem. The handling seems OK, but since it is my wife’s car, it may be off slightly and I cannot tell.

Can someone direct me to a likely component to check?

Thanks,

John

dpkreuze · #2 11-01-2006, 03:28 PM

Friend,
Does the vehicle try to level itself when the cargo area is loaded and the engine is running?
This symptom you describe may be due to a failing pressure supply to the level control.
dpk

jcwells · #3 11-01-2006, 03:48 PM

OK, I will heavily load the rear tonight and see if I can determine that it is pressurizing correctly. I do know that it pumped the correct amount of fluid into the system initially without any problem (it was empty from the work I did).

Thanks,

John

Bob Weir · #4 11-02-2006, 03:41 PM

From what I've read on this forum, The thumping and transmitting every bump in the road do indicate malfunctioning self leveling system.

Three things to check:
1] You might still have air in the system. There's a bleeder on the level controller (passenger side near rear axel where all hydraulic lines feed into).

2] Level controller has linkage connector to the sway bar. Sometimes the clamp on the sway bar comes loose.

3] Hose from pump to reservoir goes bad.

Bob
PS Hope you have better luck than I'm having with mine. I had accumulators replaced, now it just stays up and manually moving the self adjuster doesn't change height.

Good threads to reference are:
http://www.peachparts.com/shopforum/showthread.php?t=48451&highlight=Hydramatic+suspension+education

http://www.peachparts.com/shopforum/showthread.php?t=85061&highlight=Hydramatic+suspension+education

jcwells · #5 11-02-2006, 07:50 PM

I had a trans cooler line go so the car is sidelined again (it never ends). I'll replace it tonight and then get back to the suspension issues.

I did have a chance to load the back end of the car last night and I did not sense any movement or lifting of the car. I then put it on the hoist running, disconnected the adjuster and moved the value up and down. I could not see any movement in the suspension, which isn't surprising since I assume it's at full drop but I thought I might see or hear something. Nothing. For what its worth, when I bounce the rear by jumping up and down in the hatch area I get about 6 inches of travel, and good dampening

Question: How fast does the system change the car ride height?

Thanks for the points, with respect to Bob's comments:

1. I have not bleed it from the control valve yet; the information I read suggested that the system would more or less bleed itself as the car is driven. But I will try it, I'll put the car on the hoist, engine running and open the bleeder with a vinyl tube attached and see what I get.
2. I put in a new adjuster and the arm and clamp are fine.
3. Hoses and lines are now fine after my work.

With respect to buckwheat's comments I will have a look at this area.

Thanks,

John

Bob Weir · #6 11-02-2006, 08:09 PM

jcwells
"Question How fast does the system change the car ride height?"

When mine was operating; automatically in about 10 seconds.

When manually operating Level Controller; up almost immediately, down within a few seconds. Goes up faster than down, but it's scary to be laying underneath when it's coming down.

Bob
PS "sidelined again" Sounds like mine. Fortunately, Today, I only had to redu vacuum lines and connectors to cure my fluctuating idle. I used the $2 per ft silicone stuff from the dealer. I wanted to be sure of a tight fit.

jcwells · #7 11-02-2006, 11:21 PM

Replaced the transmission hose and did a fluid and filter change as well. It had been on my list and I had the parts.

While the car was up, I loosened the bleed screw (difficult) and even with the engine off I had a nice fountain of fluid flowing out the screw, with no air. So there is no air at that point.

In addition I inspected what appear to be simple donut rubber bushings at the top of the struts and they appear fine. I am sure they would be harder than new, but they are not broken up.

So next I will put the car on some ramps and crawl under with the car on and see if I can get the suspension to rise and lower.

Any other suggestions?

Thanks,
John

Bob Weir · #8 11-03-2006, 09:34 AM

If you don't have the Repair Manual CD, I can email you the 11p pdf to pressure test the pump & control valve.

Bob
PS My cars are always much more cooperative when I lay my 8 lb sledge and 4 ft crowbar alongside my tool box.

jcwells · #9 11-04-2006, 11:45 PM

Well I put the car up on the ramps this afternoon and after disconnecting the adjustable link, I moved the arm up and down with the car running, and low and behold it worked. After doing it a few times the fluid level dropped in the reservoir so clearly the system had not purged itself from just driving it. Actually the height adjuster has the valve lever so low I don't believe this car has ever run at anything other than its lowest setting regardless of the cars load.

The ride is much better, almost there. I may still do the rubber bushings at the top of the struts and see if that improves things some more.

Now a question: How do you set the proper rear ride height without the factory tools mentioned in the shop manual? I can clearly see the hole in the arm and the slot in the valve but how much weight should be in the rear in order to line these up?

Thanks
John