rear levelling system "bottom out" - system works?
 

When I first got car (85 300 TDT wagon) rear end was drooping. Found leak in hydraulic return line - by passed it (temporary fix - will put steel line back) - filled fluid (MB) - adjusted valve lever - rear end raised! No leaks - have not put fluid in for several weeks now - (Have new filter and more fluid for flush) But when driving over (something like) a speed bump - the front "absorbs okay" - but the back seems to botom out - a slight "thud" is the only difference. This is while driving over slowly. Are there any rubber parts I should look into changing? I read on forum that (126 model) had rubber mount for differential. Does 123 have this as well? Also - rear subframe rubber mounts? Is this a DIY job? I also read that if "spheres - accumulators go bad - they will leak and there is no movement in height - locked up? (Car does move up/down when pushed down on) I assumed that either the spheres are good OR not good - no in between.
Thanks STEVE.

From what I have read there is more of a shared function.. so that test will not isolate completely your problem for diagnostic purposes...

My wagon thunks a bit over speed bumps too, even after replacing the spheres. The spheres have a nitrogen charged bladder and space for the fluid inside. When the bladder ruptures the whole sphere fills with fluid and you loose some of the shock absorbing. Bad spheres ought not to affect the up and down movement any, that should work even with bad spheres. I think leathermang is right though, the spheres are more than just for shock absorbing but I'm not sure what else. They are not horribly expensive and pretty easy (although a bit messy) to replace. As they seem to be the rear suspension item that fails most often you may want to just replace them. It should help but I wouldn't expect it to make your thunk completely go away.

When the nitrogen is gone, the rear suspension cannot compress, only the tires will act a springs. "Hard ride" doesn't really describe the sensation.....!

A clunk going over bumps can be a number of things, including a loose strut mount! Top or bottom, make sure there is no play.

This suspension is fairly soft, too. But even so, a thump usually means something else is wrong -- subframe mounts (easy to change on a W123), or diff mounts. Diff mounts will cause a thump on shifts, too.

And last, check to make sure the spare tire isn't loose on the clamp -- my brother had to buy a new tire for the 300TE a couple years back on a trip, and the tire place managed to cross-thread the hold down (how I cannot imagine!) -- the tire was bouncing around , made a thump and low speed and prduced a loud drum on the highway.

Peter

My SEC thunked over bumps after the cells were replaced also.

The fix is to replace the shock bushings. When you open the cover you`ll see the top one, and it will look ok. It`s the bottom one that is bad. When the accumilators{cells} are bad it hamers this bushing.

I changed mine no more noise and a better ride.

John