From suspension bushing shoes/brackets failed - why?

[Tromas]

Fellas,

About 3 years ago I changed the front suspension bushings on my 1979 930 due to squeaking noises. Over the last 6 months the front suspension started making again, and it got more and more severe, so I thought it was time for new bushings (again). This weekend I took the front suspension apart, and to my big surprise the squeaking noises didn't come from worn bushings, but from the bushing cups (for lack of better description) which connect to the steering rack.

One bushing cup is cracked at the way through!
On the other bushing cup the spot welds for the support bracket part is cracked, and the pieces have separated completely.

Has anyone else experienced something like that, and can offer a good explanation to the root cause of this? This really puzzles me.

[WinRice]

I call them outer sleeves, don't know what the Germans call them.....

First of all it looks like you have a little rust and metal loss which probably helped the cracks start.

That second photo shows the best info. Looks like the crack started at one of the welds from mount to sleeve, probably from being overstressed by the twisting motion of badly binding or too ridgid bushings.

What kind of bushings?

[Tromas]

Originally Posted by WinRice

I call them outer sleeves, don't know what the Germans call them.....

First of all it looks like you have a little rust and metal loss which probably helped the cracks start.

That second photo shows the best info. Looks like the crack started at one of the welds from mount to sleeve, probably from being overstressed by the twisting motion of badly binding or too ridgid bushings.

What kind of bushings?

I had to go look at the invoice from 2015 when I changed the bushings. They appear to be Daystar Poly Graphite (99 3014 340). I put them in December 2015.

[s5uewf]

Just a guess that the bushings were not allowing enough rotational flex or actual twisting, so the torque was transferred to the casing and mount, which eventually fatigued

[911tracker85]

I just changed the bushings on my A arms with elephant racing rubber. one part of the installation is to twist these brackets to a certain angle to the arm. easy to do at the time you press them in as they are still lubricated, but once dry they do not want to move. it appears the idea is to preset the static angle to be the normal resting location. then the twisting during driving is only +/- that. you may have not set that correctly when you replaced and then there was constant twist and that would get worse under driving conditions. just a guess.

note the protractor in the pic.

[WinRice]

Originally Posted by Tromas

I had to go look at the invoice from 2015 when I changed the bushings. They appear to be Daystar Poly Graphite (99 3014 340). I put them in December 2015.

That’s what I would have guessed. Poly graphite are very tricky to fit to allow proper rotation. Too tight and they bind up badly and the suspension doesn’t work properly, too loose they rattle and clunk. And in areas with temperature change, if you fit perfectly in the summer, they shrink and are loose in the winter. Opposite winter to summer.

After using dozens of different types of poly bushings on various car builds, fitted, special greases, zerk fittings, etc., I’ll never use them again in rotational applications.

Don’t get me wrong, they work fine if you want to stiffen areas like body mounts, subframe mounts, crossmember mounts, etc. non-rotational applications.

Find some fresh outer sleeves and do what 911tracker85 did for a long term solution.

[full quack]

If you are not overtly concerned about your car being "stock", then I'd highly recommend you go with Rebel Racing front control arm bushing/mount kit...they are superb beyond words and gorgeous!!!!
No clunking, no squeaking, no binding and even are serviceable with replacement wear sleeves, although I have 40K miles on mine with absolutely ZERO signs of any wear.

My .02 worth.

Mark