I was under the '87 the other day working on the timing belt, and noticed a threaded hole on the rear bearing cap of the front lower control arm. Any clue what it's for?

Here's a crappy cell phone pic.

 

Andrew,

Those are for the shock-absorbers that were part of the original engine-mount system. The original mounts were solid rubber (#2 below) and the shocks (item #18) provided damping, just like a suspension system. (Oddly that page in the PET is titled "engine suspension"- look up '78 model year, main-group 1 sub-group 9).

The solid mounts and shocks were replaced in '83 IIRC by the hydraulic mounts which were internally damped (and self-collapsing). And of course many folks have replaced those with aftermarket solid rubber mounts (although I have never heard of anyone retro-fitting the shocks), and now with Volvo hydraulic mounts.

The mystery of course is why Porsche continued to machine that mounting boss for all those years-- unless they were secretly planning to go back to solid-mounts and shocks

 

Ahhh yes. Thank you Prefessor Jim. Obviously I didn't take good notes back when I had my '82.

It is interesting that they continued to machine that part. I think that's what made me think maybe it was for use in assembly, alignments, etc. Anyway, mystery solved. Thanks.

 

Machining stopped some time between '87 and '92 MY.

 

I plan on using those to bolt a full under tray too.

 

The '89 Japaneese S4 that I just worked on had them.