Both Ball Joints?
 

It seems to be a fairly common recommendation out there that, when one ball joint goes bad, both should be replaced. Is this simply an upselling tactic or is there some good reason I should replace both?

Thanks.

It has been standard advice and procedure in all books that I have seen for 40 years.
The steering is pretty important...
How much would you save only doing one ?

AND you will want to have the car aligned... either when you replace both of them... or after each time you replace one of them....

Are you referring to those on one side of the car or both sides ?
Note , I may not be using the nomenclature which is proper for MB front ends..
so you might need to be more specific for your question to get answered well...

I know my left lower ball joint is bad, so what I was wondering is if there's a good reason to get both left and right lower ball joints done.

I have Firestone's lifetime alignment on my 92 and was thinking about getting it on the 91 (the one that needs the ball joints). I know people on this board who wouldn't trust Firestone to replace a wiper blade, but I've had pretty good experience with them. But apart from that possibility, you're right....it's pointless to pay for an alignment twice.

There are some components in a front suspension which , if you replace just others, will wear out faster...as all the pressure or movement which was being shared is now taken by that one loose one...
Are you talking about the ' ball joints' ... and I put that in quotes because MB does not call the upper one a ball joint..... so are you talking about one or two items on one side... or the matching components on both sides..... which would go along with the general rule that you do not do anything to one side of an axle that you do not do to the other....
Have you checked on the price of these components ?

The logic is simple for ANY dual parts on any machine.

They were put in together at factory.. if one has failed how
far do you think the other one is behind in doing the same thing ??

TnBob, I certainly think both ....or all four.... should be done at the same time..
but we are dealing with old cars... what if the PO had replaced one side ( having not listened to us.....LOL ) just before selling the car ?
I say measure both sides... if either needs replacing do both... and would probably need several other support items in there too... like the control rod bushings..

Matching components on both sides; both lower ball joints (as opposed to just doing one).

I checked my parts supplier. It has "ball joint" and "ball joint boot." Relatively cheap. What would the upper one be called?

Well worth going through the front end carefully and maybe even replace the "almost" worn out items since you'll have it apart anyway (and need the alignment) You may not want to handle the lower ball joints (they're a PITA) but pretty much the other major components just bolt up and are straightforward to do.

I had it in to the dealer for a "free service clinic." Basically they look over my car, note needed repairs, and wash it, while I raid their deli platter and watch the NCAA tournament in the waiting room. Of course, this is an upselling opportunity for them. So they recommended 1) lower ball joints, 2) front A frame bushing, 3) front sway bar bushings, and 4) shock covers. But they basically admitted there's no pressing reason to deal with the last three.

Wow...Shock Covers! Can't say I've ever been recommended to address those! :)
What are the forums' thoughts on doing P.M. and replacing tie rod/etc??

I'd do both, if I do it myself I've been known to do all four on my fiero (155k) and truck (210K). Its a pain to take it all apart, so if you're already in there.... do them.

As far as my memory goes... shock covers are not installed on all cars and are only called for in places where there are bad/dusty roads... read about that in my chassis manual just this morning... LOL

The upper ball joint is called an upper control arm.. I think it is meant to be bought already together..whereas the lower is a normal type ball joint and cover...

Maybe it's different on the W123, but I replaced just my driver's side lower ball joint. Didn't seem to affect alignment, but then again, my steering is pretty loose. I guess I could just replace the passenger side one too, but I'm a broke and lazy S.O.B. and I've got other far more pressing issues.