915 transmission shifting

My '85 Carrera has the sometimes-balky 915 transaxle. As other owners are probably aware, these things have personalities of their own when it comes to shifting. Sometimes shifting is as smooth as silk, and at other times it's a struggle to get the shifter to go where you want it to go. Swepco 201 helps, but its not a magic bullet for these sometimes tempermental transaxles.
One thing I've found is that the thing shifts gracefully when IT wants to do so.... and WHEN it wants to shift depends largely on the speed of the car. For example, if I want to shift into second (say, from forth) while turning onto another street if I don't force the shifter, but keep steady pressure on it, it will easily slip into second when the speed of the vehicle has slowed to around 10mph. Trying to get it into second while going faster is sometimes a real chore. I'm convinced that the shifter is somehow very dependent on the speed of the car at the time.
Anyway, what I wanted to throw out was the following info. on the website of a competing Porsche parts supply store... they offer to rebuild the 915 transmission, and in their little introduction included the following:

"Some of the most common reasons for transmission to breakdown are the following: 1.) Neglecting to change the Gear Lube. Over time the gear lube loses it's viscosity and becomes too thin to protect the gears properly. 2.) Shifting into gear without "fully" engaging the clutch. 3.) Down Shifting from 5th to 2nd or 4th to 1st or any downshift skipping a gear in order. This causes the dogteeth to engage forcefully and ultimately causing the transmission to pre-maturely fail."

I have never heard of such a thing.... going thru all gears to get to a lower gear.... does anyone else follow their advice to sequentially downshift the car to reduce to a lower gear? I always shift from 4th or 5th to 2nd gear when I make a turn onto a different street, then start out again in 2nd... Am I ruining the synchro gears by doing so?
Regards,
jlex.

My 915 causes me the same grief--but I never skip gears (especially since 5->4->3
shifts so nicely). I'd imagine my motorcycling reinforces that habit (motorcycle gearboxes are sequential). One of these days I'll just get a rebuild and be done with it.

One thing I have noticed--when these cars are being driven the way they're meant to be (i.e., fast and hard), I rarely have a shifting problem. It's only in traffic and on slow streets that I get all that graunching.

blue
'81 SC Targa

I am going to the swepco 201 this weekend. Hope it helps a little. I loaded it with havoline about 2 weeks ago to flush it. Mine balks a little, like you say, when putting around. my 2nd gear syncro is ailing though, grinds a little on quick shifts. Hoping the swepco will buy me a little time.

Originally posted by jlex:
My '85 Carrera has the sometimes-balky 915 transaxle. As other owners are probably aware, these things have personalities of their own when it comes to shifting. Sometimes shifting is as smooth as silk, and at other times it's a struggle to get the shifter to go where you want it to go. Swepco 201 helps, but its not a magic bullet for these sometimes tempermental transaxles.
One thing I've found is that the thing shifts gracefully when IT wants to do so.... and WHEN it wants to shift depends largely on the speed of the car. For example, if I want to shift into second (say, from forth) while turning onto another street if I don't force the shifter, but keep steady pressure on it, it will easily slip into second when the speed of the vehicle has slowed to around 10mph. Trying to get it into second while going faster is sometimes a real chore. I'm convinced that the shifter is somehow very dependent on the speed of the car at the time.
Anyway, what I wanted to throw out was the following info. on the website of a competing Porsche parts supply store... they offer to rebuild the 915 transmission, and in their little introduction included the following:

"Some of the most common reasons for transmission to breakdown are the following: 1.) Neglecting to change the Gear Lube. Over time the gear lube loses it's viscosity and becomes too thin to protect the gears properly. 2.) Shifting into gear without "fully" engaging the clutch. 3.) Down Shifting from 5th to 2nd or 4th to 1st or any downshift skipping a gear in order. This causes the dogteeth to engage forcefully and ultimately causing the transmission to pre-maturely fail."

I have never heard of such a thing.... going thru all gears to get to a lower gear.... does anyone else follow their advice to sequentially downshift the car to reduce to a lower gear? I always shift from 4th or 5th to 2nd gear when I make a turn onto a different street, then start out again in 2nd... Am I ruining the synchro gears by doing so?
Regards,
jlex.

i've got a pretty freshly rebuilt 915 in an '85 carrera. with only about 1500 miles on it at this point, and even after the swepco 201 (which helped immensely, by the way), i still fight with mine consistently under specific conditions.

i replaced all components that showed any wear, whatsoever, INCLUDING the very expensive ring and pinion. mine still doesn't like to shift when the rpm's are low (under 3000 rpm). when i drive in a spirited fashion, though, it's always smooth as silk, in upshifts and downshifts.

the only thing that really bothers me at this point is that i feel like i can't just casually drive the car slowly in traffic (shifting at low rpms) without being sometimes distracted by this baulkiness. warren has generously suggested several adjustments i can try that might help; i must confess i haven't tried any yet, since i'm on the road constantly with my job. i am going to keep trying things here and there, though, and keep everyone updated if i find anything that helps.

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Adam Nitti
ajnitti@mindspring.com
www.adamnitti.com
'85 911 Carrera Coupe

The thing that's bothered me the most about the transmission care tips was the sequential downshifting advice. I can't believe that can be true.... my John Deere riding mower doesn't have to go thru all the gears to get to 2nd, so why should my Porsche?
I'm beginning to think its not a true Porsche-advised requirement, but something a transmission rebuilder came up with in order to make sure the driver isn't forcing a lower gear when the rpm's are too high.
Am I crazy, or is everyone out there downshifting thru all the gears first to get to a desired lower gear??? Up until now, I though that choosing the proper gear to match the speed of the car was the right way to do it, but now I'm not sure.
regards,
jlex.

Hi,

No, You're not the only one.
I often switch from 5th to 3rd or 4th to 2nd when it makes sense.
As the 915 is "bulky", it takes something longer, but it works fine.
The speed difference between the different gears is increasing when you jump a gear, and therefor time for synchronizing takes a bit longer.
No problems with that so far, but don't push too quickly.

Jens
'76 CIS with '73 body conversion

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My 85 915 grinds badly when I shift into 2nd
from any gear and i have replaced the syncro
and dawg teeth.Whats up?

I installed one of these rebuilt transmissions this summer. I also saw this quote, and was wondering the same thing.

If you are travelling at 100+ and need to make a quick 90 turn, do we have to hit every gear on the way down? Yes, as mentioned, on my motorcycle I had no choice, but with my 911, I can't seem to effectively hit all gears?

As for the rebuilt tranny, so far I have not had any issues. I am still tweeking the shift coupler to get the gears to match correctly, (i.e., at first, reverse and 5th were almost impossible to use, now everything but 3rd is good).

But, I now have an oil leak, hopefully just the sensor, so the 911 is back up on blocks as I research this.

I'd like to here some more comments on the shifting patterns.

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'80 911-SC Targa

The only advantage I can think of for shifting down through the gears is that you won't get lost. These shifters really are junk. There is no gated feel to help you know where the gears are. While driving down the road pull the shifter out of gear into neutral and remove your hand from it. Now you're in trouble. There are a few bandaids out there that help such as short shift kits, spring loaded assists, and full on race shifters. I'm going to rebuild my tranny later this winter and install some of these bandaids. I'll let you all know how they work.

The only real consideration I can think of is increased synchro wear due to having to spin up or spin down the input shaft when making shifts across a wide speed range - ie 5th to 2nd. I'll go 5th to 3rd, but tyically I try to hit most of them.

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Mark Szabo
1986 911 Targa 3.2

The 915 gearbox is notorious for its idiosyncracies and it can never be made to behave like a Japanese gearbox. It is an ackowledged fact that you should never hyrry or force gearchanges but always be smooth and wait for this fraction of a second until you feel through the lever that you can make the perfect shift. It is also true that the faster you go the better the quality of shifting.

I had my 915 rebuilt some 4000 miles ago and it it gradually loosening up. However, sometimes it is not easy to go out of 3rd gear and I need to pull more than I should.
Any ideas? Is it a matter of the new sychros being worked a bit longer or should I suspect something bad?


[This message has been edited by Renos (edited 10-18-2000).]

Renos,

I have the same problem with my new 915 rebuild. Sometimes the gears will stick in 3rd & 4th (or have a hard time getting into), but normally they are fine. I had the rebuild done 2k miles ago.

Rich
'86 Carrera

Renos / Rich

I just had my tranny rebuild also. After I reconnected the shift coupler, reverse and 5th did not shift at all, but 1,2,3, and 4 worked like a charm! After lots of fine tuning adjustment, I was able to get these to work OK. But, during the process, 3rd and 4th (but mostly 3rd) are difficult to engange.

I'm sure, with some more adjustment, we all could get 3rd working properly with a new rebuild.

Possibly, we need new coupler bushings, No?


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'80 911-SC Targa

Mully:
Try adjusting your clutch cable to see if it eases the grind into third. Mine eased up considerably after very carefully adjusting the cable & clutch pedal travel .
Renos/Rich: I've had the same problem with a sticky 3rd gear from time to time... it must be normal with these things.
Like the thought that things may ease up after a while following synchro work... my 2nd and 3rd synchros were replaced in my '85 Carrera about 2500 miles ago... maybe a break in period will help.
Am also going to try the sequential downshift thing, although it sounds crazy to me.
regards,
jlex.

Wayne has a pretty good procedure for adjusting the shifter coupling under "tech articles". It improved mine somewhat.

Double clutch your down shifts. I heard this at a PCA tech session this past spring. The advise came from a guy with a nice fleet of GT3's. The time lost per lap is nothing compared to the tow back to the pits was his logic. For those who are a bit lazy or trying to save a blink or two he said you could push the shifter into neutral as you unload the drive train. (clutch out come off the gas... car to neutral) now clutch, heel toe and grab the proper gear. I found it takes a bit of practice but every car I drive now hits the gear I want smoothly
david

A couple of thoughts about the 'advice' from the other website ... PURE BS, BALONEY, & LUNACY!!!

The 'sequential shifting' nonsense is a way of stating the obvious that rpms need to be matched as closely as possible between engine and gearbox ... but the obvious exception (and there ARE many others) is a hairpin corner at the end of a long straight, going from 4th gear to 1st, and going through the gears in order is simply not practical while you are standing on the brakes ... HARD!

Thie simple fact about gear oil is that it never thins out! It usually thickens a bit due to high temperatures in transaxles, and the VI additive (viscosity improver) boils off over time due to its' volatility. The BIGGEST PROBLEM with old gear oil in 915's is contamination with wear products ... metal particles in the oil that tend to accelerate wear and tear on the synchro components and gears ... making shifting baulky and 'graunchy' when rushed.

Anyone wanting to see a real 'horror' story inside a 915 should take a look at pages 340-18 thru 340-25 of the new Bentley manual for the '84-'89 Carrera! There is a 2nd gear set with multiple broken teeth on the 18 tooth driving gear!!!

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Warren Hall
1973 911S Targa

Ah, the UPS man cometh and he bears swepco 201. All is well. Or at least as good as it gets.

Another item I forgot to mention: I've noticed that while putting steady, light pressure on the stick to shift into second gear on a turn, the ease with which the shift can be accomplished depends somewhat on the terrain... namely, a left turn makes for an easier shift than a right turn, or a bump in the road (such as railroad crossing) allows it to go into 2nd gear more smoothly....
I suspect that what we're really experiencing here is a "flexing" dynamic of the car that can either aid or hinder a smooth shift. Perhaps its motor mounts or bracing that needs to be replaced or looked at.... my suspicion is that in a lot of instances of a "balky" shift, it's really related to the geometry of the car and the alignment of the shift rod to the transaxle rather than a problem with the transmission per se. Perhaps German tolerances are too close and can't accept a variance that may be caused by the attitude of the car body. Has anyone replaced their motor or transmission mounts and experienced a better shifting pattern with the 915? Any comments?
regards,
jlex.