redtdi96

80 SC 915 tranny quest? shift detents

I have my engine tranny out. Is there a concept of detents in the shifter when you shift gears. The detents provide a bit of hold in each gear when shifted. If there are detents is it easy to change the springs.

I plan to look at tranny internals as while it shifts OK, I want it to shift at least as well as my 80 Fiat 2000. While I just don't think the "bus shifter" will ever approach any Japanese/ Italian car I want to get the best possible performance.

My complaint is a vaugness in shifting. I have replaced the shifter linkages and installed a short shifter (literally the best mod you can make to an SC), I'm hoping that I find a problem when I open the tranny. It seems when I shift into a gear I'm not really sure if I'm there. I use a micrometer to adjust the linkage as it is that touchy!

I have driven a 96-- 911 and yes they did finally get it right, as you can shift with one finger!~

theiceman

Ia m not dure what detents are but you can certainly by after market shift gate setups from Wevo. a 915 is certainly not a g50 but I would suggest driving another 915 before you determine if yours is broken.

Certainly the 915 is different transmision but once I got used to mine and learned its characteristics I think it shifts very well.

Daniel Dudley

I have had many 124s, and a 915 box does not quite shift like that. BMWs shift that well or better, and G50s are the silky dream you are thinking of. However, Gary Fairbanks is the guy who will make your gearbox purr, and then you will know what a nice 915 shifts like.

If that is not your problem, maybe you want an aftermarket shifter like the Wevo unit.It will make it easier to guide the stick to where you want it for each gear. I have no idea which aftermarket unit is best, but I'm sure they would all be an improvement over stock.

DARISC

A correctly functioning 915 trans is not really vague at all. The stick always causes the chosen gear to be engaged at the same position of the stick, each and every time.

True, there is not much tactile guidance offered by the transmission to the hand trying to guide the stick to the correct position where engagement occurs, but that correct position remains always the same, shift after shift. With experience and practice, the driver learns these positions, not by feel, which is admittedly lacking, as just said, but rather by muscle memory, not unlike an accomplished golfer who doesn't consciously think about his every swing but rather lets his muscle memory take over repeat the same swing every time. When muscle memory takes over, percieved feelings of vagueness disappear.

Similarly, for example, a guitarist's or violinist's fingers and hand motions are guided by muscle memory.

I enjoy shifting my 915 and have come to feel that it has been maligned by those who have driven it briefly and declare it to be a bad piece of machinery but who wouldn't pick up a guitar for the first time and condemn the instrument because they couldn't play it.

SeattlePorsche

I don't think the detents are the problem. Two of the detents can be accessed from the side of the tranny and you can replace the springs, but I don't think that would do anything. There is also a detent in the diff housing and the intermediate housing. Those you are supposed to make sure they are in the correct position before you reassemble or you could end up engaged in two gears at the same time and are in trouble. If your tranny shift is vague, maybe it is the shift bushings. Or maybe you are adjusting the shifter incorrectly. The worry would be broken internals. I am only guessing here, but if it is dogteeth or syncro rings as the problem you would hear grinding. But if your hubs are broken it might not engage. I would look at the tranny drain plugs for magnetic debris if the adjustments or bushing changes fail.

I would consider changing the short shifter to the stock shifter. The 915 needs the extra time for the sliders to friction up with the syncro rings before engagement. Things need to be spinning at the same speed. The short shifter rushes that and can screw that up.

Peter Zimmermann

I'll echo DariSC's thoughts, I don't find anything vague about a correctly functioning 915, quite the opposite, in fact. Trying to compare using a 915 to a trans in a different car is somewhat like trying to make a burger taste like a Filet Mignon. Many cars have the manual trans located directly below the shifter, eliminating the few feet of linkage in a 911, so even a G 50 won't shift like other cars, they're different animals. First, I disagree with your statement that a "short shifter is the best mod...", it's more of a personal preference, in addition to who made the shifter. Factory units are wonderful, the odd assortment of aftermarket ones can range from fair to horrible (no, I'm not including Wevo products or gate shifters in this comment, I've never even driven a car with Wevo components). I might add here that I've driven 911s with 915s more than 300K miles. Also, replacing the shifter linkages is an odd term, because there are many parts, but the bushings are the ones that'll give you trouble. If something in the linkage system, between **** and coupler, was overlooked that can produce a sloppy feel. The detents inside the 915 simply guard against putting the trans into two gears at once. There are no optional detent springs, because changing the "feel" of the trans is not their job. Adjusting the linkage is not hard, and you certainly don't need precision tools, but you do need to have the basic order of things clear. It's all about being sure that the bottom few inches of your shift lever is vertical in neutral. Simply, that assures that the lever will move the same distance whether you chose to use 1, 3 or 5, or go the other way into 2, 4 or R. Your next adjustment is to make sure you can engage first smoothly by moving the lever to its left stop and pushing forward. When you test drive the car your final check will be your 5 to 4 shift, if you knick R you will have to change your left to right setting slightly. Your objectives are:
1. Bottom of lever vertical in neutral
2. Engage first from left stop
3. 5 to 4 shift (done above 50 mph) should be smooth.
If all of that is correct, the bushings are good, and the neutral gate is adjusted correctly, and you still have issues, I respectfully suggest that you have someone extremely familiar with 915s test drive your car. If it's too late for that the factory manual lists synchro ring measurements, but many factors including internal shift fork adjustment will also be in play. Good luck with it!

redtdi96

darisc really describd my issue, you need to know where to put the shifter. Shifts are deterministic, but vague. I replaced the shifter bushing and the rear coupler. The short shifter is porshce OEM.
The short shifter really improved the shifting by 5x, just a great mod.
Three other 911 owners have driven the car and they think it shifts fine, but I expect more.
I can cleanly shift through the gears, but I have to limit the shifting speed motions.

I'll find out more when I open up the box. Such a great car , minus the shifter to tranny interface that these buses have! It has about 60 k miles on the clock, Ive owned it since 2000 and have never been happy with shifting.

I guess everyone is pretty happy with their 911- 915s, so I may need to accept the technology of the SC.

Clipboard

Grasshopper. You have already made the two key statements: "...but I have to limit the shifting speed motions (sic)..."; and, "...I may need to accept the technology of the SC." See. You have already figured it out. I agree completely with DARISC and of course, Peter. If you just work your way thru the shifter setup sequence (and there is no extra problem like transmission or motor mounts) after you look into things and get it together, you will probably have what there is to have. Enjoy it.

redtdi96

well this the last chance. I have tranny apart, bought 4 syncros, 1-2 & 3-4 sliders and 2cd gear dog teeth. If this does not allow my 911 to shift like a sports car I will just need to move on. I have three people drive the car and they had no complaints on shifting, they all owned 911s.

I must admit the tranny is very straight forward, nice robust design. Now I just need to get it together and into the car....ok

I borrowed this great thread tidbit from Pelican, the topic of this thread was simular to mine:

Well, that "built for racers who know how to shift" theory is very nice, especially coming from those who have never raced! While this may not be particularly helpful to redcoupe86, here are a few points to ponder:

If the 915 was (at any time in history) so well made, why are there so very many after-market improvements, even from Porsche itself?

If this were not an extremely problematic area, why are there VOLUMES written here, and everywhere, on how to improve or work around the problems?

Do you have any idea how many racers (and experienced track guys) have ruined perfectly good motors while shifting "up" from 4th to 5th at 6000 RPM, and finding themselves in 3rd? (There are FOUR such cases that happened in events we were running!)

Our freshly rebuilt, completely adjusted, short-shift kit, 915 costs us an estimated 1/4 second per shift on the track. At The Glen, for example, there are 14 gear changes per lap in our 911 racer. Most racers who we know would not want to give up 3 1/2 seconds in an entire race - much less a single lap!

And refering to "older technology", until this spring, we campaigned a 1984 Reynard Formula Continental. It has a Hewland Mark9 gearbox made at the same time as our 915 arrangement. Shifter throws are short, precise, 3 inch movements. There is never any doubt about which gear will engage next. We shift that smoothly, too, but in microseconds! And, if one wishes, by matching revs, one can shift WITHOUT TOUCHING THE CLUTCH.

Or, maybe it is just us . . . . .
Ed LoPresti

SeattlePorsche

You didn't need to replace 1st dogteeth? They are usually the worst (I am told.) I also replaced all the brake bands at my mechanic's recommendation, John Walker. It will shift fine, but there is a bit of a break in period where the sliders wear in the syncro rings a little. JW told me to just go back and forth on each gear like 40 times each gear to get the wear in started. He also recommended not using Swepco right away, but rather a dino GL-5 rated lubricant. Since you aren't doing fifth, maybe you should flip the syncro ring over to the less worn side. FWIW mine shifts awesome now after a month of daily driving. Good luck!

Daniel Dudley

Interesting thread on pelican about the Rennsport shifter. Sounds promising. Spring centers on the third /fourth plane, and has a reverse lockout. All good stuff for reliable gearchanges.

I have an SC, and also an 80 928. The 928 has a honking long and heavy driveshaft on the front of the tranny, so there is a lot of momentum on the shaft. Shifting it used to drive me crazy, now it's a zen thing. German cars are never going to have Italian brio, but they have a real presence to them. If you want a Porsche to make you feel like a better driver, it ain't gonna happen. They will however make you a better driver. Takes a little while to grok it. Also, a tranny guru will do things like check endplay and inspect the shafts for runout. Worth considering if you want the best from a 915.

BTW, one of the nicest driving cars I've ever experienced was an 89 911 speedster. Later Carreras are fine cars, and the G50 tranny has a really super feel. The 944 turbo gearbox is equally nice, and they handle like well sorted Fiat Spyders, only much faster. I'm not that far from you in the Hudson Vally if you ever want to test drive a nice turbo. A real quality feel, shifting and otherwise. Porsches really took a quantum leap in driveability starting in 85 with the 928, 86 with the 951 and 87 with the 911. Most of it was the gearboxes, with some of the usual Porsche evolution thrown in. Worth considering, if you aren't getting what you want from your car.

redtdi96

no 1st gear dog teeth were acceptable, and it shifted in all gears with no grinds.
At some point you gotta stop the gushing.

I still need to re-assemble, which I'm sure will bring me back to the forum. I have taken apart a VW 020 trans and the 915 is much easier to comprehend and take apart.