Transmission Linkage Failure, Conical Screw Drop Options

[ctc911ctc]

All Teeners!

When I rebuilt this car with my son('74, 2.0), each step I scoured these pages for failure and success stories. trying to do the right thing during each part of the rebuild.

So, when it came time to rebuild the tranny linkage, I bought all new bushings, cleaned all components, greased as recommended and installed NEW conical screws in the middle and back of the linkage.

Today, my son called me from the side of the road - fortunately, he was close to home, he said he could not shift gears, that the shifter came disconnected. (IMG:style_emoticons/default/WTF.gif) I went to him and drove in second gear back to the garage. (IMG:style_emoticons/default/sad.gif)







Seems the Conical screw came out, my son went back to the road where the linkage came undone and he found the SCREW! (IMG:style_emoticons/default/huh.gif) (IMG:style_emoticons/default/huh.gif) (IMG:style_emoticons/default/huh.gif)

Here are my questions:
1. Anyone ever have this happen?
2. There was a spot of gray locktight on the threads when I installed, should I put some RED locktight on it as well?
3. Torque - how much Umph should I use?
4. Might the coupling threads have stripped? the picture is with a phone held under the car - I will put it on stands tomorrow and start the rebuild.
5. Might there be different sizes for these from Porsche part dealers? Might the one I have be too small (loose fit)?

After he came home he was hating the car pretty hard, took an hour and then he was back at it with wrench and screwdriver - ready to go......

Thank you ALL Teeners!

[poorsche914]

1. Anyone ever have this happen?

Yep... just this past week in fact.
The last several times I drove the 914 I noticed the shifting was becoming an issue. Getting difficult to hit especially Reverse and First.

Began an engine swap project and when it came time to remove the shift linkage, saw that the cone screw at the rear of the linkage had worked its way nearly out (IMG:style_emoticons/default/dry.gif)

(IMG:style_emoticons/default/driving.gif)

[brant]

when the screws are new, they have a spot of nylon bonded into the threads and it works as a Nylock type screw essentially...

when they have been installed and removed 5-10 times the nylon dot wears off....

I used to try to use loc-tite
I had much better results with purchasing a new cone screw that has fresh nylon and just replacing the screw...

they don't come loose for me any longer and I bought a couple of extra screws to carry in my emergency spare parts kit.

pelican sells them... I'm sure most 914 places do also

[Superhawk996]

Don’t take this the wrong way but it shows signs of having been stripped initially and then having ignored it for a while as it progressively loosened.

That statement is based on what appears to be an oval hole and thread remnants on the screw.

I know these screws can be a bit fickle but I literally drove my original car for over 100,000 miles over almost a decade without having any issues with this conical screw that would have left me stranded. This isn’t a highly torqued screw. As mentioned the nylon nub on a new screw is sufficient to prevent screws from simply loosening and then falling out quickly if under torqued. Any poor shifting ( well worse than normal (IMG:style_emoticons/default/av-943.gif) (IMG:style_emoticons/default/driving.gif) ) is a prompt to check the linkage rather than to continue driving and forcing things.

Just to be clear, not placing blame. It’s a lot easier to detect degradation if it’s daily driven vs intermittent use of a toy car where it’s easy to forget what normal is.

At this point best plan is to replace the coupler. Depending on damage to the threaded hole, it may be fixable with a heli-coil.

It is a problematic design as far as joint design goes. Look at @bbrock s build for the hex head conical screws he had made. If the length of the screw is designed right, the stretch of the bolt can be made to occur between the hex head and the coupler and it won’t be at risk of losing torque. That hex head to coupler joint doesn’t have potential for relative movement and loosening due to movement. The trick is to size the length to get full engagement to the conical taper in the rod while simultaneously getting the hex head to contact the coupler.

@bbrock

[914forme]

(IMG:style_emoticons/default/agree.gif) Or clean it up, weld it up, drill and tap the new hole fresh, and new screw. If they where a bit longer, I would safety wire them.

I started safety wiring 914 screws back in the early 90s. When one would fail, I would fix the issue, then fix it for ever.

Thats just me (IMG:style_emoticons/default/screwy.gif)

[Superhawk996]

Could definitely safety wire Bret’s hex head conical. (IMG:style_emoticons/default/aktion035.gif)

[bbrock]

(IMG:http://www.914world.com/bbs2/uploads/post-20845-1553206685.jpg)

[ClayPerrine]

Just find a conical screw from a 356. They stand proud of the coupler, and have a 8mm square head that is already drilled for safety wire. I have one on Betty's car.

[poorsche914]

This Set Screw Repair Insert might work for you.

(IMG:style_emoticons/default/driving.gif)

[ctc911ctc]

*******UPDATE*********

My local hardware store is about 200 years old - Family name SHATTUCK. The Great-great grandson owns the operation now and has near everything I could want. Haven't been to Home-Depot or Napa in years.

They have a complete set of metric...........,well....... everything including metric inserts for repairing stripped threads. Bought an 8mm set, used it and the Conical screw went in perfectly.


I then reinstalled the shift bar - back first and used RED lock tight in the back. I then installed the front with a big gob of red lock tight. I asked my son to wobble the shifter a bit and I saw that there was still about 1/8 inch of play in the fitting......Hhhhhhm.....had him do it a few more times and I was able to get a quarter-turn of the Allen wrench each time he wobbled the shifter. After 5-7 times the play went away- one more good turn of the Allen wrench and I was done.

Theory: Last time (prior to the conical screw falling out) I did this part myself without a helper and my guess is that I did not have the conical screw seated perfectly. Makes sense since the shifting was a bit wonky since I rebuilt the shifter assembly (all plastic parts, etc)....... This little bit of play is was what caused the screw to start to move, strip the threads and then fall out.

Advice: after tightening have someone man-handle the shifter RIGHT-TO-LEFT aggressively and look for motion between the two shafts.

Beer Time (IMG:style_emoticons/default/beer3.gif)



Thanks Teeners!

[Superhawk996]

(IMG:style_emoticons/default/biggrin.gif) Glad to hear you were able to fix it with an insert. Always hard to tell how buggered things are from photo's. Obviously a whole lot cheaper than a coupler.

Next step: Teach the young'un to drive it home in 2nd for himself so save you some work! (IMG:style_emoticons/default/happy11.gif)

(IMG:style_emoticons/default/beerchug.gif)

[ChrisFoley]

Red Loctite seems like a bad choice to me as it's meant to be permanent. Blue Loctite has always served me well when re-using cone screws.

[Superhawk996]

Red Loctite seems like a bad choice to me as it's meant to be permanent. Blue Loctite has always served me well when re-using cone screws.

(IMG:style_emoticons/default/happy11.gif) Too late now.

If it ever needs to be removed in the future, the trick to loosening red locktite is heat.

[Coondog]

Been there done that, happened to me a couple months ago. Now I keep a spare and Allen wrench in my glove box.

[ClayPerrine]

You could always replace the coupler.......

(IMG:http://www.914world.com/bbs2/uploads/post-1143-1531611810.jpg)

This was the shift linkage on my six conversion before the installation of the Cayman transmission and cable shifter.

I used a leftover 914 steering U-Joint. It fixed the problems with the bushings falling out of the coupler, and it only cost me the time to cut and weld the rods. It still uses the cone screw at the rear of the side shift linkage.


I put the same thing on Betty's 914. No problems with it at all. Easy to remove to drop the motor.

[ctc911ctc]

************* UPDATE II **************

Took the car out yesterday, was able to replace the MPS with my spare to pursue the surging trouble.

I wanted to test the conical screw fix and the car shifted from 1st to 2nd as smooth as I ever remember any 914 I have owned. coming out of 1st clicked right into position. I am guessing that the conical screw was NEVER seated properly and the little wobble introduced was enough to make the shifting difficult.

2nd to first is still tough if the car is moving (not unusual). The car SURGING stopped as well. Fixed 2 things! So I continued and drove a little shakedown cruise from Arlington to Lexington to Winchester to Medford and then back to Arlington MA. Saw my darling wife walking the dog on the way home and she and the mutt jumped in - we did the loop again!

(IMG:style_emoticons/default/driving.gif) (IMG:style_emoticons/default/driving-girl.gif)

Darn, there are few things more rewarding than working on a project and then it coming together.

Barn-Find '74, 2.0
20K mile, last time registered was 1986

Rebuilt:
DJet
Brakes
headlights
Longs and Hell Hole
All floor panels
Master Cylinder
Rubber, everywhere - thanks 914-Rubber
carpet
all hoses
all fuel lines
gas tank rebuild
new fuel pump
hundred little electrical things
MPS
injectors
clean, clean, clean
minor body work
major paint job

Drives like a dream - more pictures to come in another thread.


(IMG:style_emoticons/default/pray.gif) Could not have done this without you Teeners! (IMG:style_emoticons/default/pray.gif)