1985 w123 300TD has developed a sort of sway or wobble most notable at > 60 mph. It can be induced by getting on an off the throttle. However, it also feels unstable in windy conditions, drafting/passing trucks, and even lane changes in turns.

I won't list what I have done to this car in the past 1.5 years (drive-line and suspension related since that is probably what's pertinent here) since it's easier to list what I have not done.

If it's NOT listed here I have done it already:

• tranny mount
• rear trailing arm bushings
• differential (there is some drive line slack I think is pinion related, but I have done carrier bearing and flex discs)

Wagon does have SLS which is working fine and has been rebuilt (including new rams, spheres, rebuilt valve, bushings for top of strut/rams). Subframe mounts have been done and entire front end has been done (all bushings, struts, sway bar ends, bearings, control arm bushing, and on and on...).



All wheel bearings are done and end play is to spec. Tires inflated properly. No strange tire wear, car rides and performs fine at slower speed (at least the wobble/sway is not noticeable).



So aside from the three things I have listed above is there anything else I am missing? One more factor is the sway seemed to be more noticeable after replacing CV axle, spheres, hydraulic rams which was done all at once recently. Tough to say if symptoms did get worse after this or I am just paying closer attention.



Ok, tried to lay this problem out thoroughly but let me know if other info is missing.

i did reply to a years old thread that had a similar issue but decided to start a new thread since that one did not have a solution posted anyway.

__________________
1984 w123 300D anthracite (bought from fellow forum user rwthomas1, now approaching 300k and doing great)
1985 w123 300TD white (probably also from another forum member, ebay purchase, my problem child)

If we look at your symptoms, and zero in on the sway that you can induce by throttle, it would seem the item that is/could be changing is the alignment (specifically toe) of the rear end. As you apply power the wheels tend to toe in and as you let off the throttle the tires will tend to spread which could end up toe'd out. After all that work on the rear suspension including R&R of rear axle shaft, it may be reassembled right at or very close to zero toe. This condition would be very sensitive to throttle changes. The feel from the drivers seat could be described as a wander, a sway, or like the rear axle is 'hunting' for the correct track. In general the car may not be tracking exactly true. If its just one side that's off, that side will fight with the other side to track along the thrust angle causing the vehicle to seem to want to sway side to side. A quick check of the toe (empty then loaded) and the thrust angle (empty then loaded) may help you nail this down. Don't forget to move the load from one side to the other, this simulates side loading due to cross wind. Watch the angles change as you add/move the load - you may be surprised. Good luck.

I left out another major detail that relates to the rear alignment.

So I have driven this car ~20,000 miles, and the entire time I have owned it the rear passenger trailing arm has been slightly bent due to previous owner damage. I know this is a major detail to leave out, but nothing has changed with this trailing arm since I owned it yet the wandering symptom is fairly recent (< 1000 miles).
Now I suppose my recent work with refreshing other suspension components has now made this rear end damage more evident at highway speed. The measurable issue with the bent rear control arm (trailing arm) is positive camber.
I have thought about the trust angle shifting when throttling off/on. I suppose I was wondering what recent change could have made this worse. Could also be increasingly tired rear control arm bushings as well (dreading that job).

__________________
1984 w123 300D anthracite (bought from fellow forum user rwthomas1, now approaching 300k and doing great)
1985 w123 300TD white (probably also from another forum member, ebay purchase, my problem child)

Go look, there's something causing too much compliance. Suspension bushings, sub frame mounts, sway bar links and bushings. It sure wouldn't hurt to replace the bent arm. I had a condition like this that was caused by the rear subframe rusting through.

I'll definitely get under there and pry stuff around, see what moves, see what's tired looking. I see trailing arms on ebay for somewhat reasonable prices as well.

Out of curiosity: what's the opinion on shot tranny mount throwing things off all the way in the rear end? I get a vibration through around 2500 rpm and I have never changed this out (even though i did engine mounts, flex discs, and carrier bearing, not sure why i skipped the tranny mount).

__________________
1984 w123 300D anthracite (bought from fellow forum user rwthomas1, now approaching 300k and doing great)
1985 w123 300TD white (probably also from another forum member, ebay purchase, my problem child)

The Mercedes driveline system is unusual. It has only one u-joint. Apparently this is intended to raise the fundamental high enough to allow you to run to 14000 RPM, I can't imagine you do that too often. The rubber disks cushion some vibration, but are really there to allow the engine mounts to have compliance under high torque. The entire system can only be completely vibration-free when the engine is perfectly in line with the differential. So if the engine or transmission mounts are compromised, you have a good chance that there will be excess vibration, which can damage the rubber disks and eventually ruin driveline hard parts. Misalignment is especially hard on the u-joint, since it isn't paired with a second, out of phase joint. I like replacing the engine mounts and transmission mounts as a set for that reason.

Check that right rear tire - you are looking for a 'lump' or uneven edge wear (get the car up in the air, spin the tire while watching the tread - any deviation from true is the lump). It will be subtle, and caused by the positive camber wear. That is most likely the wobble component of your ride issue. Swap it out with a good full size wheel/tire assembly (maybe from your '84) and take it for a test ride. Get the camber issue corrected before going much further (replace the bent part). If you can see the difference in camber due to the bend, its enough to wreck a tire, and change the other angles significantly. Also check your ride height. You are looking for side to side differences. If present, address that also. That affects/limits the range of adjustment available while performing an alignment.

I would be highly suspicious of the trailing arm bushings. It's hard to see how bad they are until you unbolt them and drop them down. They have a considerable effect on the stability of the rear end and even the entire car.
Mine had severe body roll and felt like steering stability wasn't there until they were replaced. Afterwards, it felt like a new fun car to drive.

Rear steer has to be always investigated. May be a structural mount problem. Up on a hoist with a pry bar is best.

It is in fact rear trailing arm (control arm) bushing failure. I put the rear wheels in the air and can shift the passenger trailing arm about 1/8" (maybe slightly less) with just my arm strength.
This is also the slightly bent control arm so the whole thing will be dropped and replaced with a replacement arm and bushings.
Bummer since I recently had the rear struts out for replacement and now have to take it all apart again.

__________________
1984 w123 300D anthracite (bought from fellow forum user rwthomas1, now approaching 300k and doing great)
1985 w123 300TD white (probably also from another forum member, ebay purchase, my problem child)

Thanks, I deal with this a bit too. It gets bad with a soft or flat tire, but my 240 D behaved a lot better with a flat tire than my TD.

__________________
CC: NSA

All things are burning, know this and be released.

82 Benz 240 D, Kuan Yin
12 Ford Escape 4wd

You're four times

It's hard to

more likely to

concentrate on

have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?