w123 300td wagon rear suspension thud

[hobospeed]

Hi guys,

I have a 1985 300td wagon and I replaced the SLS spheres, flushed the hydraulic fluid and adjusted the leveling valve a few months ago. The suspension and handling were improved quite a bit and the car will level itself when a heavy load is in the rear but I'm still getting a loud thud on what seems like the rebound of the suspension travel when hitting pot holes or speed bumps. The noise is only coming from the left side of the car but only when there is almost no load in the rear, if I have three adults in the back or a couple of kids in the third row the thud doesn't appear. Are there some bushings that could be worn/missing on the actuators/struts?

Thanks,

Tim

[leathermang]

I am pretty sure this is covered in the archives.... I had a wagon once... it may be that an item which limits the travel of the axle is missing... it was 15 years ago i had that wagon... might be something with the sls also... check the archives..

[hobospeed]

Thanks for the reply.

I've tried searching the archives but haven't found anything that sounds like the same issue as I'm having.

I've tried adjusting the SLS valve to have the rear end higher and lower by a couple of inches to see if the thud changes/goes away thinking the height change would change the axle angle/spider position. After testing the thud was still there.

What part of the axle limits movement?

I've also pulled the accumulator on the left site to make sure it hasn't failed but it seems fine.

[Zacharias]

Have you looked at the spring on that side to ensure it isn't broken?

The SLS springs do way less than those in a conventional suspension setup. A broken one may be less evident.

[barry12345]

An old trick we used to do and I still would if needed. . Get a couple of guys or perhaps even three or four pushing the rear end down. Working it really.

You might be able to hear the part during the rebound and identify it. It might even be a tired rear end isolation pad. Probably best tried both with the engine on and off but not certain. Your description to me sounds like a loose or worn mount for something. Hopefully your proximity to the noise being a lot closer might help identify it.

[Rogviler]

I had an obnoxious clunk from the springs right after I did some work and had everything out. It got to be less after awhile, but a front end collision really seated the springs and I haven't had the problem since.

-Rog

[BWhitmore]

Trailing arm bushing?

[hobospeed]

So last night I put the left rear of body on stands and then put a jack under the trailing arm to watch the suspension compress. From what I can see the spring looks fine. There is a spot in the travel where there's a bit of a knock/slight resistance after about 3 inches of jacking and it appears to be coming from the strut/actuator. This spot in the travel seems to be about where the suspension would be when the car is off the jack stand and under it's own weight. I tried jacking past this point by a few inches and then quickly dropping the jack to see if I could get a louder noise but was unsuccessful in hearing anything like I hear when on the road.

What does the top mount of the SLS actuator look like? I assume there's a rubber buffer of some sort. I'm pretty sure the car was driving for some time without functioning accumulators. The ones I pulled off were both totally gone and 100% full of fluid.

[hobospeed]

Originally Posted by BWhitmore

Trailing arm bushing?

From what I can tell they do look old and I'm they are the originals. I'd hate to go through what looks like a lot of work to replace them to find out the knock is coming from somewhere else....

[BWhitmore]

Use a large pry bar to see if there is any movement in the bushings. Also check for movement in the differential mount. On the TD wagon the upper shock mounts are a bit of a hassle to check as the carpet behind the second seat needs to be pulled up.

[hobospeed]

I take it that it's best to check for movement with the wheel off the ground?

[hobospeed]

Well I found at least the main problem by jacking up the rear trailing arm and unbolting the the hydraulic strut from it. With the bottom of the strut hanging a few inches I was able to see/feel that the ball joint is totally gone. Has anyone replaced just the ball joint? I see that its has it's own part number (A0003200228 - #38 in the image below) but I'm having a hard time finding any sources, well other than the local dealer who said they can order one in for me from Germany to the tune of $280.

[Mxfrank]

Check the sway bar links. And check the exhaust mounts, too.

[vonsmog]

I just replaced both my rear shocks with ones off of a parts car with only 84k miles on it. Both of the old ones, the ball joint was shot. Now I have a nice smooth ride, just like a Mercedes should be!