Remember that broken 981-chassis Porsche Cayman I picked up for $15,000–or less than half price–then drove cross-country with its four working gears? After tearing out its transmission, it was finally time for the moment of truth: cracking it open and figuring out what really went wrong. Finally, I’d learn why fifth and sixth gear were missing.
Remember, this car fell …
All those machine tools you bought and you're not even going to just manufacture your own pin?
Woohoo! Score!
are you sure you dont want to buy a new $15,000 trans just to be sure?
Everyone loves a happy ending 
So now what are the plans for the Cayman? A potential keeper for future upgrades to produce content or a quick flip that produced a cool road trip and a few repair stories? It seems like either could be succesful but the quick flip has to be enticing .
wae said:All those machine tools you bought and you're not even going to just manufacture your own pin?
I know, I know. But it's cheaper to buy the pin than to buy the stock to make one.
Tom Suddard said:wae said:All those machine tools you bought and you're not even going to just manufacture your own pin?
I know, I know. But it's cheaper to buy the pin than to buy the stock to make one.
Plus you can sell the other 24 for $250 apiece as a specialty part that solves a known Porsche transmission weakness. Think of the dinners you could buy your mom with the profits! (I'm kidding except for the part about taking your mom out to dinner.)
Margie
Hell ya! Major score!
Was the missing .2 mm wear or just like that from the factory?
Stampie said:Was the missing .2 mm wear or just like that from the factory?
i would guess that the hole got wallered out as the pin made its exit
Gotta love that outcome. Nice!
If the 6 mm dowel is a bit loose just hammer in a 1/4", I'm sure that would be fine! Glad you found the problem, good luck with the reassembly.
Love the simplicity of the fix.
So how much labor would a dealership charge for this repair along with parts other than the pin? How many hours for a trans R&R, how many hours to crack and reseal the trans, how much for whatever unicorn tear fluid is inside? I guess it would be something like a clutch change plus a fluid fill - what's that run in Porscheland?
Sweet!
Is the hole diameter 6mm on both the steel selector shaft and the aluminum shift fork? Or did the aluminum shift fork get wallered out somehow? A lot of transmissions use roll pins/spring pins in this application to compensate for this wear.
So I learned that aftermarket aluminum shift forks can soak up more heat on track... enough to expand and cause the roll pin to fall out. My for ever fix has been to tap the fork and shaft together to put a bolt in. Leaving just a little untapped spot so the bolt bottoms out in the threads at the same time the head seats on the fork, jamming it in. No more problems
If the transmission is considered an un-serviceable module , I wonder why they didn't Loctite the pin or weld the fork together.
(I think we can all guess the answers, it's a rhetorical question.)
RacetruckRon said:Is the hole diameter 6mm on both the steel selector shaft and the aluminum shift fork? Or did the aluminum shift fork get wallered out somehow? A lot of transmissions use roll pins/spring pins in this application to compensate for this wear.
I wonder if this is a solid pin due to expected loads? Seems unlikely for a shift fork. I agree that I would consider a roll pin as well. I know that Subaru uses 6mm roll pins and that Pete has the special tool for them :)
I'd give the rest of those pins the stink eye while you're in there. Great work!
Wow, that is some amazing luck! I have to wonder if the non servicable part is to avoid laws requiring them to supply diagrams etc. i have to imagine they ship the cores Back to porsche and they do something with them.
Keith Tanner said:RacetruckRon said:Is the hole diameter 6mm on both the steel selector shaft and the aluminum shift fork? Or did the aluminum shift fork get wallered out somehow? A lot of transmissions use roll pins/spring pins in this application to compensate for this wear.
I wonder if this is a solid pin due to expected loads? Seems unlikely for a shift fork. I agree that I would consider a roll pin as well. I know that Subaru uses 6mm roll pins and that Pete has the special tool for them :)
Who knows with the Germans. The CD009 boxes I've torn apart every joint in the shift selection system is double roll pinned. 6mm pin with a roughly 3mm pin inside to minimize flex of the larger pin. Seems to put the failure on the aluminum shift fork itself. I've seen a couple Nissan CD boxes with a snapped 5/6 selector
I would have slathered it with JB Weld and peened the end.......this maybe why I work on Datsuns.
Nice! Why does this sort of thing never work out for me? If I tried this, I'd probably spend endless weekends disassembling/reassembling a transmission and eventually give up and replace it.
To answer a few questions:
It's my theory that Porsche just had a batch of slightly undersized pins. I'll measure it more carefully during the repair--this was just initial measurements with a pair of calipers--but 6mm is a standard pin size. I intend to put the new one in with bearing retaining compound and peen the edges of its (and the others') forks to make sure this doesn't happen again.
As far as labor, I think the entire removal/disassembly/repair/reassembly/reinstallation could be completed in a day pretty easily. It took me about an hour to open up the transmission and find the problem, but I was being extremely gentle and that includes a fair bit of camera setup and finding a bench/orientation that was comfortable to work on. Next time I do this, it'll take me 10 minutes.
I'm not going to use spring/roll pins because they're more brittle, and over time would break from the force applied to them wiggling them back and forth. I think the correct answer is a dowel like Porsche used, except properly sized.
Machinist here, I would ream the fork and shaft to a common size and pin it. Definitely remove the slop or worn portion that caused this problem in the first place. A coiled roll pin has a lot more strength than a normal roll pin, that's where I would look. Coiled pin are over sized so will fit tight in a standard reamed hole. May need a carbide reamer if the shaft is too hard.
I have taken apart a few pre WWII machines assembled with tapered pins, those do not come out unless told to.
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