MM951

So Van got that broken lower shock mount of my trailing arm. 2 welders said it was impossible We also learned there is a steel insert in the trailing arm where the bolt goes. I believe Van took a few pics of this. Hopefully when he gets back in town he can post em.

The bad news is the threads are gone. Van and I are exploring options but either way, its progress. As soon as I have a new trailing arm on there I can enjoy my car again

mike

Will Feather

Knew you couldnt sell it...

GOOD LUCK!

JonH

Glad you are getting the car back on the road, nice work Van. So what was the consensus on the failure? Did you conclude it had to be the shock mount bolt not seated on the trailing arm or something else now that you have a closer look?

Van

Getting the broken bolt out was the easy part. Just weld a lot onto the top of it, weld on a nut (or, in this case, two) - then back it out!



As for the actual cause of failure, I think it was not having the shoulder of the shock bolt fully seated onto the control arm. The threads right at the break were "closer together" showing that the bolt did some bending before it broke. I didn't get to see the other piece, but perhaps the end of the cut threads also allowed for a stress concentration point for the crack propagation.

Whatever the actual failure, it begs the question, why didn't it torque down fully? The end of the bolt threads show obvious deformation and rounding usually associated with cross-threding or some kind of burr in the hole. This control arm seems like it has seen a hard life (multiple helicoils in other locations), so it's quite likely the threads were damaged previous to Mike's taking it apart.

I took a file to the mounting surface, and was surprised to find that there is a steel insert in that aluminum control arm. All this time I assumed it was aluminum threads, but in fact they are not. From the factory, a steel insert was placed into the aluminum (probably during the casting process).

I was also surprised to find that a bolt (I had a stock one on hand) just slides into the hole before the threads engage. I do not know if this is stock or if this part has been previously damaged!! I've heard some people say, "oh, yeah - the bolt slides part way in to reduce cross threading potential." And I've heard people say, "nope - thread-engagement the whole way."

My car's not here right now - so I have nothing to compare it to. Does anyone here know? Before attempting some kind of thread repair, I want to verify that this condition is NOT normal - I don't want to "fix" something that Porsche has intentionally done. But, on the other hand, it seems odd to me that the thread engagement would be that minimal, and because it's a long bolt, there's a long area that just "floats".

Anyhow, here's a video showing how the bolt "drops" in - I look forward to feedback.

xsboost90

which side is it - IIRC i have one rear trailing arm up in the rafters...

Van

Driver's side.

VOoDOoGTX

dosent look normal at all.

VOoDOoGTX

Obviously this car was not designed with the mechanic in mind and that would lead me to believe that this bolt was not made too "reduce the risk of cross threading." anyway this aint no kia the people that are expected too work on this are smart enough too know how too thread a bolt in.

Lorax

Mine isnt like that

Rock

Dropped and well concealed

MM951

FWIW the other side dropped in like maybe 1/4" and had solid thread engaugement the rest of the way.

When this broken one was installed, there was no obvious gap between the shoulder and the trailing arm. After this broke I checked the other side - which looked fine - until I checked behind it and there was a .003" gap. I think the bolts are a HAIR too long for my trailing arm (who knows, as Van said it looks like it was man-handled with all the thread repairs previously done on it..) so they bottom out as the mount is almost flush -so even though it looks like its fully seated and there is plenty of torque - and the resistance I felt was the mount bottoming out, not being tightened.

The pass side replacement mount went in no problem
I'm pretty sure I know how to install a bolt. In the years and thousands upon thousands of bolts installed/removed, engines built, etc never had a problem with a bolt backing out/being impromperly removed7

Thanks, but we will see. I'm picking up a new car on Saturday..while it's not exactly what I want, it is similar to something I really want. If the time comes that I have to sell a car to pay for tution etc and I like the new car enough....

harrisonrick

I vote the title "addict" gets changed to "Van the Man".

aben8057

I just finishded up a rear suspension job. The bolts drop into the rear control arms exactly as you have described. For the record I have an 86 851.

mclarenno9

+1 I remember the same thing when I did my suspension last spring.

Van

So, Mike, maybe it's supposed to be that way. In which case, I think we should ask Ground Control about their thoughts (if I get some time tomorrow afternoon, I'll try to give them a call)...