911 - 915 tranny shift linkage issue/mystery

[joe_72T]

Hello Guys and Gals,

I am not a mechanic but like to wrench on things and I would appreciate if anyone can help me figure this out. It's a 72 911T with a stock 915 tranny and shifter. Shift coupler is newer and not worn. Car runs very well but every once in a while (like twice a season) this happens:

-when I am parking it and putting it in 1st gear or reversing I loose the gears. They are all mixed up. Reverse is where 2nd was, no 1st, hard to get the shifter into any other position. It's like the gears are in a big knot.

-I then remove the cover over the coupler, loosen the coupler completely and go over the linkage adjustment procedure and tighten it all up. Bingo, works perfectly fine and shifts smooth as butter in all gears.

-Car runs fine for a few months and then rinse, repeat, same thing!

I don't think the coupler bolts loosen up over time as I really tighten them as hard as I can. The tranny is very smooth otherwise and I use Swepco.

Any help would be appreciated. Thank you in advance,
Joe

[HaroldMHedge]

Have you checked the bushing, 914-424-224-00, under the shifter which holds the shift rod?

While your in there, I would also replace the ball socket, 911-424-139-00 or 911-424-139-01.

[proporsche]

Hi Joe.as mentioned replace the shifter socket .Pretty easy job. 4x 13mm socket and 2x 10mm socket pull up the shifter tower and replace the ball socket.The other round is most likely ok they do not do bad ...
ivan
no 23

[carreradpt]

Also take a good look at the coupler bushing. When it starts disintegrating it can cause those symptoms.

[joe_72T]

Thank you guys,
Those parts seems to be fine as I have checked them when I first had this issue a while back.

Is part #30 in the above diagram a lock washer? I don't believe I have one in my set up. Could that be the problem?

[proporsche]

Hi.if is your shift rod tight and you do not have the washer no big deal but eventually put it there.You probably have nut with silicon.
Did someone work on your transmission,lately?There are some safety pin which could be misplaced.
Here is some reading
https://www.porscherepair.us/porsche-911-1984-1989/transmission-reassembling-915-transmission.html

Ivan

[ASD]

I had similar issues until replacing the pin screw. new coupler - lost adjustment, and screw was not holding. Had to replace it.

[joe_72T]

ok ty,

Proprsche, yes I had the transmission worked on a few years ago.
ASD, Is the pin screw #26 in the diagram?

[ASD]

not sure from the pic, its just ahead of the coupler in the tunnel

[Jdub]

If you elect to swap the oil in the near future have a look at the guide (not shift) fork that sits on a plate by way of three studs and often can loosen up. You remove, clean, and blue Loctite the studs to the plate after draining the oil and removing the plate from the trans. Have a new gasket in hand when you do this - very worthwhile check to perform and you may be surprised at what you find.