Why the LCA bushing has the hexagon instead of round hole?

[digger]

noise can be an issue, but the inner ball joint is bolted to the subframe and it's also a noise source similar to the proposed rear ball joint altough this one is closer to the cabin. I also think the ball joints with zero plays would not cause a lot of noise.

My Citroen SM has zero rubber joints on all the suspension parts which are either ball joints or roller bearings, and no noticable more road noise than other cars. It's a flying carpet.

it needs to be isolated for NVH to suit their wide purpose use (not a race car) in which case if you are properly isolating it the ball joint you not really benefiting from it being a ball joint hence it is a waste of money

[digger]

Today I filed the hex end into a smooth surface for it to rotate inside the bush, lubed the shaft and bushing with grease for low friction. Will see how long it will last. Done on a 325iT car.

Stock shaft:

Filed shaft:

oh jesus

[sapote]

the ball joint you not really benefiting from it being a ball joint hence it is a waste of money

Longer life than the stock rubber bushing, less work for us.

[sapote]

Willing to have the creaking noise, if it ever happens, and gradually worn down bushing vs the sudden total ruptured rubber and a gigantic free plays on the suspension.

[Slideways]

oh jesus

..

[sapote]

I also think why they didn't use a ball joint here instead?

I have been dreaming about this ball joint. But it's almost impossible to be able to mount the LCA (or any plates) at 2 points, inner ball joint on subframe and at the frame, which requires high precision, otherwise there will be intererence issue. It's impractical for BMW to ensure the distance from the ball joint on the subframe to the rear one on the frame horn is a constant to match the same distance on the LCA.

[digger]

Longer life than the stock rubber bushing, less work for us.

Longer life more NVH pick your poison. There is a trade off in every design decision

[sapote]

Longer life more NVH pick your poison. There is a trade off in every design decision

I will pic the precision suspension of all ball joints with some NVH over the quieter rubber bushing that will last only a few years. Btw, this "rear BJ" subjected to L/R loading only during braking, and very little load from the wheel up/down motion so road noise should not be a big concern.
But as I said it's impossible to mount 2 BJ on a rigid frame.
But this's a good mental exercise.

[old///MFanatic]

Today I filed the hex end into a smooth surface for it to rotate inside the bush, lubed the shaft and bushing with grease for low friction. Will see how long it will last. Done on a 325iT car.
Filed shaft:

FTL

[jayjaya29]

You really let your intrusive thoughts win here. Enjoy your sloppy front suspension.

[George Hill]

To clear up some misinformation, the E36 (and AWD E46) control arms are round, yes, but that is not to allow the arm to rotate in the bushing. In fact BMW specifically states it should NOT rotate in the bushing. When those bushings are installed onto the arms I use turpentine which softens the rubber for install. The car is then set at ride height (quickly) and bounced to settle the suspension. Once the turpentine dries the rubber is "stuck" to the control arm and will not freely rotate.

I imagine BMW moved to the hexagon configuration for ease of installation and still prevent the arm from rotating.

Also note, the M3 control arm bushing is solid, not oil filled like Non-M. In my experience the M3 bushings last vastly longer than Non-M which have the history of early failures.

And from the BMW E46 xi repair instructions

[sapote]

And from the BMW E46 xi repair instructions

"Non-fonformance with these procedures could lead to serious impairment of handling"

Appreciate the information.
I'm trying to think what serious issue could happen if the shaft end allowed to rotate in the bushing, consider how many times we had driven a car with the bushing completely torn apart. The worst I can remember is the pull to the side during heavy braking, but this happened bc the torn bushing let the wheel be pulled 1" or more rearward. This won't happen if the shaft just rotates in the bushing, wear gratually.

The normal wheel going up/down on the road, e.g. speed bumps, road surface, cause the LCA rotating in the bushing with little or no radial force pushing on the rubber, so low wear. This same rotaing arm stresses/twists the bushing in stock setup, leading to fatigued ruptured bushing.

[digger]

It will likely "just" flog out much much quicker and have much less stability as there is progressively less material supporting the load and excess free play meaning deformation under load will be higher which is contra to what the goal with this thread seems to be. A round pin rotating inside the round bush will wear very quick as the pin nor bush is particularly hard wearing material so you need a rod end to do this job which brings the obvious compromises.

[sapote]

I installed a new bushing on the rounded shaft end on 6/6/2026 . Will let you know how long it will last.

[sapote]

It will likely "just" flog out much much quicker and have much less stability as there is progressively less material supporting the load and excess free play meaning deformation under load will be higher which is contra to what the goal with this thread seems to be. A round pin rotating inside the round bush will wear very quick as the pin nor bush is particularly hard wearing material so you need a rod end to do this job which brings the obvious compromises.

This broken bushing inner sleeve shows the metal ring R outer layer after the hex rubber which is about 2mm thick. So if the rounded shaft worn down the hex rubber part, metal ring R will act as a bearing for the shaft to rotate, preventing the rubber bushing B from ruptured as on the stock part.Worst case this will have 2mm plays instead of more than 20mm plays with the completely ruptured donut B.