Observations while shifting my 915, what does it mean?
 

Can anyone provide their opinion on what these symptoms could be related to? I'm wondering what is making my 915 so finicky.

This post is in regards to a 1981 SC with a 3.0L with a 915.
1. If the air pressure in one of my back tiers is low, it becomes very difficult to shift.
2. When everything is bone cold (California winter mornings), It becomes very difficult to shift.
3. Just after everything warms up shifting improve greatly.
4. After driving in stop and go traffic for long periods of time it becomes very difficult to shift in to 1st and 2nd.
5. When approaching a stop shifting improves when I let of the breaks.

My Conclusions:
The angle of the transmission is changing relative to the shifting linkages. I wonder if it is related to the engine and transmission mounts. Could they be getting old?

Could the shift linkages connecting the shifter to the transmission be bent? The previous owner drove the car with a cut down factory shifter and warn bushings. The car use to be very hard to shift. Did some damage occure?

Any input would be appreciated!

-Arron

Have a look at your motor mounting supports , if they're broken or too old the engine can affect shifting when moving (a big warm-up for example).
That could be an issue....

I have the same thing. Cold mornings are a pain.

If wearher very cold , it's normal that the shift is hard 'cause of the gear-box oil .

How can people who live in suburban California and the south of France have any comprehension of what "cold" means? There are thousands of us driving 911s in truly cold temps--down to 10F below, typically--who don't have any of these problems.

Maby your body is cold and somwhat shivery so your not shifting like you would if you were comortable. :) But seriously, yes the mounts could be bad and the oil thick when its cold. You might try a different oil thats less seseptable to the cold. Also some of your simptoms like improving when you let off the brakes could just be that your engine speed in relation to the trans speed happens to mesh better at that particular time.
If i drive my porsche like i would a normal car i would get nowhere. I almost always blip the throttle between shifts and heel toe when im downshifting and it works just fine :)

By no means was I saying it is cold here in California! :D

I just need a point of reference.

:P Have a medal. You live in a colder place Wilkinson.

Is it necessary to live in the North Pole to give a reply ???
And i never said that south France was very cold.
I just try to reply and help .

http://images3.hiboox.com/images/0107/dej51p6o.gif

your 915 is 27 years old. maybe rebuild? what oil do you use? swepco is recommended.

I have the same issues with my 915 when it's cold, but not necessarily when the ambient temperature is cold. For a reference point, I live in Los Angeles.

1) What I've found is the transmission needs to get a little warm before it shifts well.

2) The transmission - at least mine - shifts much better above 4,000 RPM than below. I don't know why, but it does.

3) I had worn engine mounts, so I switched to solid mounts sold by TRE. They made my shifting much smoother and quicker with little to no vibration.

4) Southern France in climate is similar to Southern California, especially in summer. :)

I'm fairly sure that swepco was used during my service. I'll double check.

from your trouble after driving in traffic
maybe it isn't the tranny but the clutch that needs attention?

Did changing to sold mounts affect anything else? Do you feel more vibrations from the engine?

The clutch is new. It was replaced when the engine was rebuilt 2,000 miles ago.

No. No vibrations at all. Maybe a vague buzz, but I must be used to it now.

I do know the car has continued to feel more exact when cornering since the mounts were put in. They seem to hold the engine in well.

You might consider checking the clutch adjustment. Even a new clutch would cause shifting problems if it isn't adjusted correctly. It takes all of 10 minutes to adjust, including drinking a beer after you are done.

JR

915 shifting
 

915's are very easy to adjust for linkage issues. Get out your Bentley and follow the procedure as outlined there for the connection behind the seats in the tunnel. Also allow some time for the transmission to warm up. All of my trannnys (except the Boxster) feel more slick when warm. In the case fo the 915, it doesn't really act smoother until the engine is a full operating temps.
I fiddled a bit with a short shift kit (Porsche) and making adjustments to the shift coupler in the tunnel until I found the sweet spot. You will know it when you find it. Follow the procedure first...then make changes one or two splines at a time to find the smoothest shifting.
911_pilot

I have not had any transmission related problems since when I first purchased it. I knew that the 1-2 syncros was bad. It would not go into 1st gear, but the car has more than ample power to use 2nd gear to start off from. I made the repairs and it has been great ever since, I also later on, replaced the coupler bushings and adjusted the shift rod. This has been close to 10yrs ago. From your description, it could be a few different things causing your problems. The first thing I would check are the mounts, then shifter coupling for bad bushings and bad alignment, etc. Start with the simplest things first, then work your way up the "harder to do" list. The 915 is a transmission that takes time to learn, just how YOUR, particular transmission feels and shifts. I have found that different cars certainly have a different feel to them, even though they are all 915 transmissions. this is in part due to the various states of the bushings and various adjustments of the shift rod. Good luck!!