1987 TDT keeps breaking sway bar brackets - Page 5 - PeachParts Mercedes-Benz Forum

JimmyL · #1 07-13-2010, 05:45 PM

Quote:

Originally Posted by Rick Miley

I think people may be a little on edge after what happened last night.

What happened last night???

babymog · #2 07-13-2010, 04:10 PM

Quote:

Originally Posted by whunter

There is no way I could take this technical discussion personally.

I suspected as much, you sound like one who's more interested in exploring possibilities, always a challenge.

I agree that asymmetrical wheel heights will cause a load on the swaybar, that's what it is designed to do. Whether they are beyond the design limit is another question.

If the long-end of the swaybar is moving, or the swaybar is moving fore/aft, it seems that the fatigue would be at the top of the bracket at the 90* bend. As it is at the bolt hole, it seems to me that the stress/flex of the swaybar is at the bolt hole. To flex the bracket at the bolt hole you would need to rotate the bracket at the point between the two lower bolt holes, which would be about the axis of the swaybar. If the swaybar were being rotated and allowed to move fore-aft (abnormal behaviour) then again the fatigue point would be at the top of the bracket, the 90* bend.

This rotation would occur whether the wheels are at the same extension, or uneven. The significant difference would be the vertical load on the bracket, or pre-load.

The same thing holds true for any un-natural movement transverse to the car, it would either slide the bar in its bushings, or bind and pull the bushings sideways, which would likely cause it to fail at the upper bolt-holes where it mounts to the car subframe.

It seems that the bar is designed to rotate in the bushings on this bracket, it is a smooth bar, perhaps some rust has caused it to bind or the bushing/bracket are not the correct ones for the diameter of bar being used. I do hope that the findings will be posted, I'm curious.

leathermang · #3 07-13-2010, 03:26 PM

Are you actual engineers saying that the break was caused by something acting through the sway bar ...
or have you agreed with my analysis that the long end of the bracket is being moved by something and it is not designed to move... thus causing the break at the location in question ?

leathermang · #4 07-13-2010, 04:26 PM

Persistence of set is an interesting thing to watch....

babymog · #5 07-13-2010, 04:58 PM

I have provided forged-aluminum suspension pieces to the automotive industry for lightweight low-unsprung-weight suspensions, even domestic trucks, ... I'm not sure what part of the cast iron and stamped steel 124 suspension is lightweight. What the car is, is stiff, with 30% of the body being high-tensile steel and the highest natural-frequency chassis in the industry (54hz IIRC).