rear control arms

[JCE]

I have seen several comments in catalogs or on other forums regarding the need to periodically replace rear "thrust" arms and/or "upper control arms" on w124 rear suspensions. Some sources say every 9-10 years, others quote every 60,000 miles. Is this necessary, recommended, or just attempts to sell parts? How do I know when it is needed? Thanks for any help.

[MikeTangas]

John,

I'm not exactly sure, but I seem to remember a post a while back that described symptoms. Try doing a search for "floating rear end", or something to that effect. If I remember correctly, it was regardinga 300E, and the recommendation was to replace rear thrust bushings (I think).

[JCE]

Thanks, Mike! I did a search for "rear control arms" before I posted, but didn't find what I was looking for. Your key words on "floating" led to a good thread. I don't have any of these symptoms yet, but still wonder of there is a rule of thumb on preventative replacement.

This is progressive wear - you'll feel loose in the caboose looong before you *need* to address it.

[mbdoc]

When they are shot you can see the rear wheel move for-aft in the wheel opening by power braking in drive & then reverse. Also when deccelerating & re-accelerating you can feel the rear change the direction of the whole car! FLOATING

[dtanesq]

Someone more knowledgeable may correct me if I'm wrong, but as you may have seen from the "Floating 300E" thread you may be referring to (I can't remember if the following comment is anywhere in that thread), Mercedes apparently replaced the thrust arms for the 300E with S-class thrust arms and also replaced the bolts used to install them. I believe that this all comes as a kit. Believe me, you'll know when you need the repair and you won't like the feeling when it comes. The rear end geometry changes too easily from road imperfections and engine torque, which is what causes the rear end to move around on you. I have read in this forum and elsewhere that the old version of thrust arm generally loses its rigidity at about 100K miles. Once replaced, I don't think you'd ever have to worry about that particular link again since the beefier link doesn't fail as the originally spec'ed part does, so it isn't a "periodic" maintenance item. While you're snooping around your rear suspension, have someone take a look at the rear subframe mounts as well.