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Discussion Starter · #1 · (Edited)
I've made a video of a problem I seem to have found on the project car. I'm not sure if this is widespread, but it was on both my cars.

In a nutshell, the torque to yield screws that hold the rear diagonal strut bolt to the body seem to have come loose by themselves over time. These are critical to the stiffness and stability of the rear section of the car. One still had a little tension, one was loose.


 

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Thanks for this and it comes at a good time for me. I started to notice that my car seemed to feel less planted for the last year or so and has a tendency to feel like its wants to wander in the rear a bit as if Im wagging the tail. This was not happening at all before, and seemed to just appear one day out of nowhere while out driving on a perfectly flat and straight 2 lane road.

It feels somewhat like really worn rear tires can, or a bad alignment, so I had new rear tires installed as well as letting Porsche do a new alignment and check the rear suspension out. They found nothing wrong and the issue still persist after the alignment.

Some days I notice it much more than others, but It's time for my annual servicing so I need to check this out while I have it on the lift. My early 2014 has a build date of May 2013, so its more than 9 years old now and could be potentially suffering from this issue.
 

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Jeff, why do you suppose that the hole diameter in the strut brace is so much larger than the bolt diameter? Seems wierd unless for some reason there is a spacer that is supposed to be used around the bolt?
 

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2014 Boxster S, Racing Yellow
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I wonder if this is related to the popping sound I get in the steering column (Anyone else have pop in steering column going down...).

The one on my passenger rear frame-side is practically falling out. It's probably disengaged from the surface by at least 2 mm. Can you just re-torque those, or should I buy new bolts?

I'm surprised there isn't a TSB or recall on this.

Once again, great info @jjrichar
 
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That's crazy! I would think the oversized holes may actually contribute to the bolts unthreading even faster if the brace is being allowed to wiggle side to side a bit under load, dragging on the head of the bolt flange and possibly turning them a bit? Once loose enough, vibrations during operation can take over from there
 

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2016 Porsche Cayman
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Just checked mine and it's tight but I wonder if I should remove the bolt and add locktite thread sealer? 30 ft-lbs torque + 90 degrees won't stretch the bolt and I assume to be reusable.
 

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Discussion Starter · #8 · (Edited)
That's crazy! I would think the oversized holes may actually contribute to the bolts unthreading even faster if the brace is being allowed to wiggle side to side a bit under load, dragging on the head of the bolt flange and possibly turning them a bit? Once loose enough, vibrations during operation can take over from there
From what I've seen on other cars with this type of setup this is pretty normal. It's the clamping force between the strut and the body that is holding everything in place.

I think the large hole is there to cater for fitting tolerances as there is a lot of different pieces being connected together and this connection point is at the end of a long arm.

Just checked mine and it's tight but I wonder if I should remove the bolt and add locktite thread sealer? 30 ft-lbs torque + 90 degrees won't stretch the bolt and I assume to be reusable.
If they are tight I'd be leaving them be. What I plan to do after replacing mine is mark the screw head and where it is in relation to the strut so I can check visually if it's backing off in the future.
 

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BTW 999-072-840-01 is the Porsche part number for those bolts.
 

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Does anyone know if the "captive nut" that these bolts go into can have a TimeSert installed, or will the nut separate from the body of the car? Asking for a friend..... :) (Max it will take is about 20 lbs before the bolt spins.....)

Thank you.

-Eric

09 987.2 with a stripped nut......
 

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Discussion Starter · #14 ·
Does anyone know if the "captive nut" that these bolts go into can have a TimeSert installed,
I looked at this as closely as I could with the car on the lift. The 'captive nut' seems to be part of the body that is welded in place. A lot of that area is steel, which is unusual compared to the remainder of the body and it seemed to be very solidly in place. It was all completely enclosed with no ability to get to the inside from what I could see.

That being said it was only about 6 threads deep, so I'm not sure as to it's ability to take a timesert.
 

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Discussion Starter · #17 · (Edited)
Thank you for checking. Surprising the bolt is 40mm long if there are only 6 threads in contact (there are 9mm time-serts, so it could just work).
I don't have any experience with timeserts so this was just a guess on my part. I stuck a thin poker up the hole to see how far you could go. I didn't reach the top so you could put a very large bolt in there if that's all you had.

What is the thread pitch of the M10x35 bolt?
1.5mm. Standard M10 bolt. Just ensure it's class 10.9

After looking at the problem and seeing how much clamping force is required to hold the strut in place, it seems you don't actually need that much. I'm leaning towards using the same screw but not torque to yield. Just use 65 Nm, as this is the standard for this size and class bolt. This is going to give at least 50% of the clamping force of the torque to yield method, and I think this should be enough. I'd mark the bolt position and check periodically if it needed tightening.

I'm worried that if I have to tighten this multiple times then it might strip the captive nut out. I've had this happen before on another car (BMW E46 convertible) with a very similar setup, the same screws and the same torque to yield tightening. I had to remove/install many times due to a drive shaft issue and eventually it stripped, requiring a helicoil fix. I now just use 65 Nm and leave it be. Not had any issues with it.
 
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