915 shifting woes Down Under - 81 SC

[NBW911]

Hi new to this,
Had 915 rebuilt 4000 km's ago, bearings, synchro's etc... all normal stuff, new clutch and cable, shift bushes and coupler have been checked and look fine.
Mechanic has done many rebuilds and has been factory trained etc etc.
The car can shift perfectly one minute or even for the entirety of a trip, however the very next trip I will be double or even triple clutching all gears or maybe only certain gears not always the same gears.
Mechanic is not sure of problem, has never seen this problem before.
Issue was also present prior to rebuild, although may not have been to same degree. Gearbox is out of car at the moment in pieces again, can not see any obvious problems.
If anybody has any ideas I would appreciate it. Cheers Brendan.

[silverc4s]

It sounds to me like shifter/linkage/bushing wear and adjustment problems.

I just went through this on my '73 915, and replaced the shifter, coupler, and the shift rod bushing. Now it is unbelievably fine shifting. Of course I am a few hundred dollars lighter, too.
I did the coupler first, a bit better but still all over the place at the lever, then removed the shifter to find the rod bushing completely non-functional. Replaced it & sprung for the Rennshifter at the same time, as my shifter's internal parts were pretty much worn out.
Now I just want to go drive the car so that I can shift gears, quite a change!!

[DanielDudley]

Pilot bearing/clutch failing to release fully. A possibility, but do the simple stuff first.

[NBW911]

Silverc4s, did your coupler and bushes look OK, my mechanic assures me that mine look fine. But to me it almost feels like the selector is not aligned correctly, sometimes you get feed back through the gear stick, almost like a pulse.
Thanks for the help. Cheers Brendan

[silverc4s]

My coupler was pretty sloppy, not totally worn out but a lot of side play. The ball cup bushing was okay, the shift rod bushing was totally broken into pieces and just hanging on the rod.

The top guide plate of the short shifter was worn in the guide slots esp on the right hand side, from trying to get in & out of 5th I guess.

I'll try to get some pictures tonight if you think they would be helpful.

[NBW911]

I don't think mine are that bad, definatly not in pieces. That the strange part of the puzzle one minute impossible to get into gear in 1-5 attempts, then the next trip its as smooth as silk?????
Gremlins I am beginning to think!!!!!

[cstreit]

Heat can play a significant role... Can you think of a correlation to heat generated in the trans for one trip vs. another?

[turbo23dog]

The SC owner's manual says to ensure that the clutch pedal is depressed ALL THE WAY to the floorboard when switching gears. I've started this practice and there is actually a huge difference in the way the car goes into gear. Still have a few days where 1st needs a double clutch/slight throttle blip, but overall much better than before.

[NBW911]

I have seen no correlation at all to temperature, the car is regularly driven on 80 kilometre trips with 30 minutes of freeway driving at speeds of 110 km/hr, so I imagine temp would be pretty much steady state. Clutch has been investigated, mechanic has driven car for several days and has had exactly the same results as I get. Where to next? I don't know?
Cheers for the input, Brendan

[911pcars]

Originally posted by turbo23dog
The SC owner's manual says to ensure that the clutch pedal is depressed ALL THE WAY to the floorboard when switching gears. I've started this practice and there is actually a huge difference in the way the car goes into gear. Still have a few days where 1st needs a double clutch/slight throttle blip, but overall much better than before.

Complete clutch disengagement should be assumed when shifting, but as you say, not necessarily so if the clutch free play isn't adjusted correctly.

BTW, the "floor" is relative. There's an adjustable clutch pedal stop on the floor board. If set too high, clutch may not fully disengage. If set too low, the TO bearing travels too far and can bend the pressure plate release fingers.



Sherwood

[NBW911]

I am not sure it could be that easy, the clutch pedal stop is a fixed mechanical limit of travel, unless thier is a component of that system that can flex or dislodge I don't know how I could get that much variation???
Cheers Brendan

[cstreit]

Well obviously something is changing from trip to trip. They key may be identifying that something... .. I'd start looking at yourself first, then work from there...

[jhynesrockmtn]

When I swapped out the short shifter on one SC into the other that had a stock shifter with worn ball cup bushing I had a helluva time getting the linkage adjusted right.

I have the Seine system BTW and love it.

When I thought I had it, it would shift fine from 2-3 sometimes and then really stiff the next.

I played with the linkage more, both fore and aft adjustment and side to side. I know why the two gurus here in Seattle I've talked to don't like the short shifters, they are a ***** to get dialed in. It seems to be ok now and survived a track day recently.

Do you have a short shift kit in the car?

You probably already tried this but If you have access to another shifter, you could try swapping that in to see if it makes a difference.

[NBW911]

Thanks Jerry, I have a short shifter (brand unknown), my mechanic has mentioned he has had problems with them in the past but has reassured me that it is set up fine, although to me it sounds a hell of a lot like the problems you have had and solved. Where do you make the adjustments and what kind of adjustment is it? (spline or flange etc??)
Any info. would be greatly appreciated.
cheers Brendan

[jhynesrockmtn]

Brendan,

Take a look at the following article on Pelican:

http://www.pelicanparts.com/techarticles/911_shifting_improvements/911_shifting_improvements.htm

I got confused a bit with which direction to turn the coupler and searched the archives for some additional help. I found a simplified explanation that basically said keep the shifter in the 1-2 plane and rotate the coupler fully to the passenger side of the car. It took several tries, the first few times I got it to shift better but had it adjusted a bit too tight and hitting 3rd consistently with no hesitation was hard. I backed it off very, very slightly, and it worked much better.

My tranny was rebuilt less than 20,000 miles ago. My short shifter is a factory unit.

I might have your mechanic swap in a stock shifter in good condition as a start if he can't identify any other causes for your problems to eliminate your short shifter as a source of problems.

I would also search short shifter for feedback from John Walker on them. He's one of the local mechanics in Seattle that's not a fan of them.

[Giantman]

Bendon out of interest do mind revealing the cost of your transmission rebuild? I am about to embark down the same path up here in Qld and would like a referece point. Thanks,

Simon.