Question on Balljoints for a 99 E46

All,
There is a procedure using a huge pliers for checking balljoints. This procedure checks the movement in the joint in the vertical direction,
however the outer ball joint is supposed to control movement horizontally (affecting caster and camber). Hence the test with the big pliers does not check the direction in which control matters. Further, the rear mount of the control arm is in a rubber bushing which does allow some motion in the horizintal plane which affects caster and camber (just think of the inner balljoint as the pivot point). So we have some slop in the control of the caster and camber, and in my opinion this is by design. For me the real question is what is the real tolerance for the balljoint play, and how is it measured, given the play in the system? How do you know that the balljoints need replacing? Using the huge-pliers-test both joints are showing some motion after only 25000 miles, yet the dealer feels only one joint has slight play. I have two new control arms to install so I plan to wait a bit. If I recall right, Bentley manual says when you get vibration, but does not say much else, and does not mention the test with the big pliers. I am getting vibration above 80 mph, but not on all road surfaces. The wheels are well balanced. None of my rims are perfectly round, and I am thinking about replacing them, it seems to me that some of the washboard roads around Baltimore Maryland may have contributed. In genenral do these 17inch alloy wheels need periodic straightening or replacing. If a rin is sufficiently out of round, why is the vibration not on all road surfaces? Maybe the vertical play in the joint, and wear on the bushing, when combined is what is contributing to the vibration depending on the smoothness of the road surface.
If anyone knows the story on these balljoints, I am very interested in finding out.
I suspect it was BMW's intent for some fuzziness on the alignment, otherwise why use that rubber bushing?
At 110,000 miles the car continues to be a sweet handler at all speeds except for the vibration.
Any help will be appreciated.
Carver
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Carver wrote:

Well, sort of... The outer balljoint is the one that wears out.
The inner one is not prone to wear because, as you noted, the only force on this joint is the relatively small lateral force caused by the drag of the wheels against forward motion. The motion within the joint is limited to the angular changes that the control arm makes when the suspension flexes.
OTOH, the outer balljoint must both flex and pivot as the steering wheel is turned. So checking the outer joint is the key. On older 3 series cars you could replace the outer joint (press in and out) but I believe that on the E46'es you must replace the entire control arm, so you'll probably never see an E46 with a worn inner joint.

Correct on both counts. There is "slop" or more accurately "flex", and it is entirely intentional. But the design of the bushing is such that it primarily allows motion in the horizontal direction. This translates to allowing the wheel to move fore and aft on the car. Because the inner and outer balljoints are lateral to each other, and their dimension does not change, the camber will not vary with this flexing. The Caster is what will vary with this bushing;s flex, as the wheel moves forward and backward underneath the fixed strut top.

This is a tough one. The design of some BMW outer balljoints is such that the joint is encapsulated in a hard rubber surround that is supposed to reduce the transmission of vibration through the chassis. The will be some "normal" motion on these joints when using the "huge pliers" test. I do not know if this is true of the '99 E46es. I find it makes it difficult to diagnose.

I think your assessment of the vibration is right. I would suspect wheels and especially tires before the suspension itself. In fact, I would not suspect vibration when the joints are worn at all. I would expect some clunking on bumps when they are really bad, but otherwise it is primarily an alignment and safety issue. I have no idea where this vibration story came from.
-Fred W
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