So... there I was. Minding my own business...(pics)

[firefighter7128]

When my rear control arm snapped and left me an my 7 year od stranded for 3 1/2 hours in the sun with no water.

WANTED ASAP: Control rm for 84(Driver's Side, Rear)

[stepson]

Bummer

[Dean_Fuller]

Hi Matt,
Any way to get a photo of what and exactly where it broke. Can't say I have seen this happen before.

[Stan.Shaw]

I should have a rear control arm, email me if you are still looking Stan.Shaw at Excell.Net

[Mrmerlin]

is it the upper or lower control arm???

[Landseer]

Matt, the paint on that car looks fantastic.

If you can lift the thing pictures of the rear parts would help. Especially if you can get that wheel off.

Oh, nice umbrella.

[firefighter7128]

I only wat to move the car 1 more time. the rear bumper is now almost touching the ground.
It is he lw arm. broe in 2 dead enter. I do stll need one really bad. this is my only car and i now have my kid for the summer.

Thanks on the paint..... and umbrella. im glad i had it there. lol

[Normy]

When you get a chance...post a picture. I second that paint- that's a nice looking car.

Best of luck-

N

PS: Note to self....inspect rear suspension arms~

[firefighter7128]

Originally Posted by Normy

When you get a chance...post a picture. I second that paint- that's a nice looking car.

Best of luck-

N

PS: Note to self....inspect rear suspension arms~

On my way down in a few. going to jack up rear and inspect ball joints/tie rods...
I will take pics.

[firefighter7128]

Originally Posted by firefighter7128

On my way down in a few. going to jack up rear and inspect ball joints/tie rods...
I will take pics.

Ok here we go. Guys if you have one, i need it asap. its the only car i have.









This one is just to brighten someones day.

[Danglerb]

I wonder if that didn't start some time in the past with a jack in the wrong spot? Its not a part I recall ever hearing about breaking like that.

Left rear control arm 928 331 043 06, closest to you might be Roger at Home - 928's R Us Online Parts Catalog (calling him works best). Pelican has them for $1156 new, but a used part should be fine, $250 at 928Intl.com. Hopefully someone local will have one and cut you deal.

I think that dog has enjoyed the party a little too much.

[firefighter7128]

ya i would have to old off its 250

[flat6pilot]

The pic of the dog is great. Looks like he's been token a bit.

[Xlot]

Interesting very unusual failure.

That's the exact spot that on many cars is bent due to a tow truck tying down the car on that bit of the suspension. Its meant to be flat, but is often kinked very slightly.

[spooledx2]

Will one off of an 80 work? If so I have one. Pay the shipping and call it a Merry Christmas. :-) Hate to see you down to long I know what its like.

If anyone can chime in on the fit it would be much appreciated.

[Normy]

Now THAT is bizarre-!

I suppose that that could be a fatigue crack. I've been around 928's for the past 11 years, and this is the first time I've ever seen something like this.

That beam is part of the "Weissach axle", or passive rear-steering system that was developed for the 928. The way it works is that that particular beam is supposed to bend from straight into an "S" shape during braking, causing the front edge of the rear wheels to twist toward the driveshaft, thus enhancing stability. Most cars want to spin out in hard braking during a curve, and this system largely eliminates this tendency.

What would cause that beam to flex so much that it evenutally failed? I don't know. I suspect that the flexation involved in this suspension system comes about from carefully selected rubber bushings. I have a hypothesis: One or more bushings on your car were bad, bad, bad....and this caused excessive flex and an eventual fatigue failure.

Hmm-

N

[76FJ55]

I would be surprised if that is a normal failure mode. That plate is designed to flex as part of the weissach suspension, however the flexture mode will most likely cause the maximum stressed to be concentrated near the ends of the plate with very little stress near the center. as mentioned previously and as seen the the illustration, the plate bends to form an "S" shape. as you can see the two ends account for most of the deflection. The area in the center of the plate is actually the transition area from concave to convex section so is essentially a neutral axis exhibiting little distortion or stress.

I agree that it is most likely a fatigue failure initiating from an existing flaw or previously incurred damage. If you can get some detailed high res pic's of the fracture surface I may be able to help determine where it initiated and how much was fatigue vs overload. looking at it with a microscope or better yet an SEM would be ideal but I don't know that this failure really warrants that kind of effort and expense, and today's high megapixel cameras can do a pretty good job of capturing enough to make a good educated guess for the purpose of satisfying curiosity.

[MPDano]

Originally Posted by firefighter7128

Man, that looks crazy. Never seen one crack there. Glad all came out of this ok.

Are you sure that cookie isn't laced with something?

[firefighter7128]

That my freinds is "Stoner Dog"... and he is watching you.

Spooledx2 thank you. Can anyone confirm it would fit?

[Normy]

Originally Posted by 76FJ55

I would be surprised if that is a normal failure mode. That plate is designed to flex as part of the weissach suspension, however the flexture mode will most likely cause the maximum stressed to be concentrated near the ends of the plate with very little stress near the center. as mentioned previously and as seen the the illustration, the plate bends to form an "S" shape. as you can see the two ends account for most of the deflection. The area in the center of the plate is actually the transition area from concave to convex section so is essentially a neutral axis exhibiting little distortion or stress.

I agree that it is most likely a fatigue failure initiating from an existing flaw or previously incurred damage. If you can get some detailed high res pic's of the fracture surface I may be able to help determine where it initiated and how much was fatigue vs overload. looking at it with a microscope or better yet an SEM would be ideal but I don't know that this failure really warrants that kind of effort and expense, and today's high megapixel cameras can do a pretty good job of capturing enough to make a good educated guess for the purpose of satisfying curiosity.

Good post. I can't help but think that perhaps a dried out old bushing allowed the beam to bend in the middle instead of the ends. Look in that picture- it appears that the broken ends of the beam are bent forward, like the arm was bent in a curve with the apex forward, implying that the wheel was toeing out. This is a fascinating thread, be interesting to find out what happened.

N