Rear Shock Install - Weird Problem

[KMoore68]

I'm having a weird situation installing the rear driver side shock on my 1977 911 S Targa.

If I hand-thread the bolt into the trailing arm, without the shock, the bolt eventually "bottoms out" and I can apply torque to it.

If I line up the shock and hand-thread the bolt through the shock into the trailing arm, the bolt just spins and spins and doesn't ever "bottom out" and I can't apply any torque to it.

It is a very odd situation and I'm a bit stumped.

Has anyone experience anything similar?

I am planning on buy a tap and die set and re-tapping the bolt and the trailing arm.

Comments?

[kyngfish]

Have you inspected the threads? If the bolt doesn’t go all the way into the trailing arm when having to pass through the shock and only the top threads are stripped - this would happen.

[Schulisco]

https://www.pelicanparts.com/techarticles/101_Projects_Porsche_911/63-Shocks/63-Shocks.htm

To remove the rear shock, place a jack under the rear trailing arm and lift it up slightly. The shocks support the weight of the trailing arm when the car is suspended in air, so you need to remove this tension from the shock prior to removal.

The same is on remounting the new shocks! You need to remove the tension of the trailing arm by lifting them slightly. Under no circumstances should you recut the threads unless they are damaged.

Thomas

[KMoore68]

Originally Posted by kyngfish

Have you inspected the threads? If the bolt doesn’t go all the way into the trailing arm when having to pass through the shock and only the top threads are stripped - this would happen.

The threads on the bolt seem ok, I have cleaned them and it hasn't made any difference.

I'll try using an endoscope to see the threads inside the trailing arm tomorrow.

[KMoore68]

Originally Posted by Schulisco

https://www.pelicanparts.com/techarticles/101_Projects_Porsche_911/63-Shocks/63-Shocks.htm

To remove the rear shock, place a jack under the rear trailing arm and lift it up slightly. The shocks support the weight of the trailing arm when the car is suspended in air, so you need to remove this tension from the shock prior to removal.

The same is on remounting the new shocks! You need to remove the tension of the trailing arm by lifting them slightly. Under no circumstances should you recut the threads unless they are damaged.

Thomas

You have to raise the trailing arm with a jack to get it up to the height of the shock. I'll have to see if I can determine that the threads are damaged before I recut them.

[gled49]

Sounds like u grabbed the wrong bolt, too short. If u hand thread the bolt in say 5mm in the trailing arm without the shock, is there enough space for the shock width? The bolt should be 14x1.5 thread x85mm. BTW, the leading end of the trailing arm 14mm bolt is only 75mm long.

[KMoore68]

Originally Posted by gled49

Sounds like u grabbed the wrong bolt, too short. If u hand thread the bolt in say 5mm in the trailing arm without the shock, is there enough space for the shock width? The bolt should be 14x1.5 thread x85mm. BTW, the leading end of the trailing arm 14mm bolt is only 75mm long.

I'll confirm the length but I didn't grab the wrong bolt, this was the same bolt that I took off the rear shock when I removed it.

This is what has me so confused.

[kyngfish]

Pics of the bolt. Arm. Damper. Bolt in damper. Would help.

And looking at the threads in the control arm (no pic for that but you should look)

[KMoore68]

Pics as requested ...

[brianlay]

The bolt needs to be lined up to go in deep enough to catch the threads
As others have said, jack up the trailing arm a bit line things up
Don’t use force or cut new threads. The bolt goes in without the shock, right?

[KMoore68]

Originally Posted by brianlay

The bolt needs to be lined up to go in deep enough to catch the threads
As others have said, jack up the trailing arm a bit line things up
Don’t use force or cut new threads. The bolt goes in without the shock, right?

Yes, the bolt goes in without the shock. I'm having difficulty getting it lined up with the shock, the bolt doesn't grip and just spins.

I'll keep at it.

[gled49]

Confirm length of bolt.

[KMoore68]

Originally Posted by gled49

Confirm length of bolt.

Bolt length is 85 mm

[KMoore68]

Still struggling to get the bolt lined up, I'd appreciate any ideas or suggestions.

[EC900]

The bolt in picture looks as if threads are rounded (maybe it’s just out of focus) but have you tried to run the bolt thru without the shock? Does it catch and tighten properly? Try another (or new) bolt w/o attaching shock to confirm.
Seem to me that the TA would strip before the bolt. Lightly grease up a Q-tip and see if any alum shavings are present in the TA.
The jack under the TA can be too high or too low as it looks in the picture maybe slightly higher causing the shock to lean outwards - also could be just an illusion in the photo.

[gled49]

This is crazy, in your picture with the bolt and washer flush up against the (green) shock, it has to be threaded in. If I’m not mistaken there is a steel insert cast into the trailing arm, check inside the hole with a magnetic. The minimum thread engagement for the 14mm bolt would be 14mm. If the bolt hasn’t engaged the threads yet, as in your picture, then something is certainly wrong. The threads on the bolt aren’t damaged enough to cause your problem. The insert threads could be damaged or the insert could be turning. Measure the width of the shock bottom mount. Remove shock. Insert bolt, leaving mount width +14mm. If u haven’t engaged threads, then a repair is in order. Not sure if repair or replacement is in your Q.

[David Inc.]

Yeah the early threads on that bolt are absolutely toast. If I were to guess it probably bottoms and torques up without the trailing arm because it's getting to better threads.

You have to be very careful threading these in to make sure that the shock is aligned and there's no tension on it twisting the bolt. You need a new bolt first, though.

[KMoore68]

I'm going to measure the threads and see how much are engaging but I'm also going to order a new bolt from Porsche and see how that goes.

[kyngfish]

I mentioned it in an earlier comment, and EC900 echoed the same thing, but what it seems like is the early threads in your control arm might be stripped, and the reason you’re able to thread it without the shock is that the bolt is grabbing “good” threads deeper in the hole.

Have you inspected the “top” threads inside your control arm? A new bolt isn’t going to fix this, that bolt looks fine if the threads are fine.

[lateapex911]

"Free thread the bolt in the TA,, but before doing that, measure where it stops with the shock.
Does the bolt grab and bite at that measurement with no shocK?

And def get eyeballs in the TA hole, see whats there.

If it's stripped, retapping it with the stock size won't help.

X10 on a new bolt.

Belmetric has a great selection of metric in all finishes and grades if getting the Porsche version is too slow/expensive/backordered/whatever.