Preventive measures - "stuck" transmission?

[TWJ]

I received great advice and information yesterday from John Walker, Grady, KTL and others regarding my "issue" with my 915 transmission being "stuck" in reverse. Thanks again and I'll let everyone know the resolution.

My new question is - are there preventive measures against this happening again? There are some good (recent) threads on items that improve shifting through replacing the shift coupler, upgrading to Swepco, professional adjustment of coupler/cable, etc. Will these measures also help guard against the shift rails (shafts) become "stuck" as well? Are the other preventive measures that might help?

Thanks again!

[Grady Clay]

TWJ,

Yes, there are improvements to the external linkage that MAY help. It depends where the problem lies. With a 915, everything in the internal and external linkage is at least “not new.”

Since the problem happened previously, I wouldn’t be surprised if a PO just got it back in place and didn’t address the root problem. I think the problem is either worn parts or mal-adjusted shift forks. I won’t discount other potential problems.

An easy and less expensive first step might be to apply the current “trick” linkage exterior to the transmission. Even if you eventually go inside the transmission, this is worthwhile and not money wasted “tilting windmills.” I’ll leave it to others more knowledgeable to advise the best parts.

I would plan to eventually go into the transmission – very worthwhile.


BTW, try and keep something like this all on one thread. It will help future Pelican searches.
A really cool aspect of this Forum is to see the initial problem described, the questions that help clarify the problem, the many proposed diagnosis, the actual discovery of the problem, the many proposed solutions, and finally the actual solution with all the trials and tribulations to get there.
I think the classic in this area is the rcecale 915 adventure.


Best,
Grady

[john walker's workshop]

in my email, i mentioned that someone probably had it apart and got one of the detents in the wrong position. that's what they're there for. so it will happen again until it's disassembled far enough to correct that problem.

[TWJ]

John and Grady thanks again for your time and your responses!

Grady - I will pay particular attention to your comments about structuring these threads for best "reuse" by others on the forum. I understand what you are staying and have reaped a fortune in information from this forum myself.

John - first of all I do appreciate your expertise and comments. Actually I believe someone has been "inside" the tranmission at least twice. I mentioned that the problem I currently have happened back in 1998 and was tended to by one of the most respected independent mechanics in the Chicago area (Peter Fischer of Fischer Motors). From the receipt I have it appears he adjusted the shafts appropriately and that was it. It would be a stretch for me to believe he did anything less than a "perfect" job (though it may have been limited). A "second generation" back PO have done a major rebuild of the car. I have the manuals and other doc's from that process and can see his notes regarding clearances etc. in the tranmission chapters. Beyond that who knows, the car is 32 years old. Sounds like going in there is needed at some point, maybe sooner rather than later.

Some years back I used to rebuild Karmann Ghia's and VW Bugs ('66 was my favorite). Although I have not done a great deal of work on the 911, I feel I understand it pretty well. Throughout my adventures the transmission has always been the component that has been a little intimidating but with everyones help here I'm begining to understand it and get some comfort level.

What are the best reference books/materials beyong the shop manuals? I have the Haynes manual, any others?

[rcecale]

TWJ,

You're already reading the best "referene material" around....posts on this board. And with John and Grady you're really looking at two of the most knowledgable guys around. Just keep asking your questions, you'll get the answers you're looking for.

Oh yeah, if at all possible, post pics whenever you can. They really help to get your point across.

Randy

[TWJ]

Rcecale, I think your right about that.

[Grady Clay]

TWJ,

As they say “There is no substitute” for a Factory Workshop manual.
Expensive but worth it.
The sections of Haynes and Bentley are valuable additions.
Even the little “Spec Book” has stuff not easily found elsewhere.
Spending some serious time searching on-line will really pay off.

Start yourself your own manual for this odyssey.

Posting every little detail on the Pelican will subject it to scrutiny from some very
knowledgeable Porsche people and will leave a legacy for the next Pelicans.
There is no such thing as a “dumb” question.
The insight from a first-time person is perhaps most valuable.
All us “old f@rts” take too much for granted.

Many of the Factory P-tools are not absolutely necessary or you can fabricate them yourself.
Most are available from our host.
Of course there are some nuts that collect Factory P-tools and then
go make their own versions. Who me?

Referring to the image below:
"
"
(C)1972 Dr. Ing. h.c. F. Porsche A.G.

If you go the route of taking the shift pivot plate #34 off, you can do
a test to see if the detent lock-outs are in place and functioning correctly.
You can put the 5-R shift rail (not numbered in this illustration but just below #12)
into R or 5 and then see if you can move the 3-4 shift rail #57 into 3 or 4.
You should not be able to engage both those gears (5 & 4) simultaneously.
Here is the detent layout:
"
"
(C) 1972 Dr. Ing. h.c. F. Porsche A.G.

The legend for this detent layout is:
1 – Gear housing
2 – Half-round dowel pin
3 – 3rd and 4th speed selector fork (shift) rod
4 – Short detent
5 – Roll pin
6 – Pin
7 – Sleeve
8 – Spring
9 – Long detent
10 – Roll pin
11 – 5th and reverse speed selector fork (shift) rod



I can’t find my diagram for the 1-2 to 3-4 detent. John, others?


Best,
Grady

[john walker's workshop]

you have to engage 5th and reverse via the main shift shaft. unlike the 1/2 and 3/4 shafts, you can't get at it thru the pivot plate hole. you can see the end of it though, and if it's stuck in 5th, the end can be pushed manually to get it into neutral. if it's in reverse, the only way is to remove the reverse switch and push the activating pin.