1st gear is from 0 to something only

never downshift to 1st unless the car is at a dead stop, or you are sure that you will come to a halt ( at the traffic lights)

1st gear just isn't designed to be used while rolling , it's just to get you rolling. anything else...2nd gear will work just fine

I agree that Sherwood has the answers. He understands what is happening in a synchromesh gearbox and thus his explanations make sense. Particularly the discussions of shaft speed matching by double clutching. Virtually all the symptoms and anecdotes discussed in this thread can logically be explained if one understands the basics of synchromesh trannys. The problems are similar in 901s and 915s. The problems can also exist in G50s but we hear less about them simply because they wear differently than the 915.

There were many different types of tranny maladys described in this thread and while most Porsche tranny problems are synchro related, there are other maladys that have little to do with synchros. The "hard shift to first (or reverse) at a dead stop" is more of a dog teeth allighment issue than synchro issue. Throughout the thread I saw no attempt to explain meshing of dog teeth between gears. These teeth the lateral teeth on the sides of the gears into which the slider gears mesh. These are what actually grind if the input and output shaft speeds are not matched properly and the teeth that are not matched if one cannot shift to first (or reverse) at a dead stop. Regarding Franc's comments """"I've noticed that if I engage the clutch for a second in neutral and then dis-engage and try 1st again, it will go."""" What is happening here is that the when you are stopped the dog teeth between the driven shaft slider gear and first gear are not alligned. If you change nothing (spinning the gears or moving the car) the gears will never engage. When you engage the clutch in neutral, you spin the slider gear on the input shaft. When they stop again, it is more likely that the dog teeth are now properly alligned and the car slips right into gear. You can accomplish the same thing if you are on an incline by releasing the brake and moving the gears on the driven shaft. This is why dropping the car into second and moving ever so slightly helps to get the car into first.

Don

Im finding out recently that its important to keep the shiftrod and its bushing well greased. Because I can really feel that shiftrod through the shifter and when its dry it really affects shifting speed. Also replace that bushing and the one at the ball cup. Cheap.
Brett

Is it normal for the 915's clutch engagement to be high on the pedal? My clutch starts to grab when the clutch pedal is within a couple inches from being fully up. By recognizing this in my car, my shifting has become a lot smoother.

Carefully, as Zeke said if you want the tranny to last. My neutral to first change is a b*tch, and i often (rolling slowly) pull away in 2nd.

And I agree with Scott - i have found shifting at high rpm on the track to be much improved.

Nicely put Bob, love the pics of your car on the other thread btw.

My 'box was rebuilt a year ago and is wonderful to drive. I agree there needs to be a very slight wait for the gear to engage between 1st and 2nd, 2nd and 3rd and the rest seem to work with no wait, matching revs makes a big difference. Thing about the 915 is that you can take a tiny bit longer to get into 2nd or 3rd, but once the change is made, the car makes that time back up by being so quick in the gears against anything else of the same era. Love it :cool:

Jack,
Great video.

difficult 1-2 shift on 915 tranny
 

I am a newbie 911 owner (84 Carrera) and this thread describes EXACTLY the experience I have had with my 915 tranny. The downshift to first has to be done delicately and I can't do it (without crunching) over 5mph without blipping the throttle in neutral (double clutching).
The bigger problem I have is with the 1-2 shift. All too often I don't pull hard enough, or fast enough, or slowly enough and I'm stuck in shift limbo, aka neutral. It can be a real chore to get into 2, sometimes going to 3 and then immediately back down works, sometimes double clutching works. It doesn't grind, however. It just balks and won't go in. It doesn't happen all the time, but it is the most infuriating thing I have noticed with this tranny. The shifts to 3rd, 4th and 5th are great, and the downshifts are very smooth as well (except to 1st).
QUESTION: can anyone explain why shifting 1-2 is so difficult yet the 3-2 downshift is easy with this tranny? I have replaced all the shift linkage bushings and the shift rod coupler, greased everything, changed transmission oil to 75w90 synthetic. If it is a synchro problem wouldn't I hear grinding when I miss a shift?

PS: Love this site! Excellent feedback from a good bunch of helpful Pelicanites.SmileWavy

I've noticed that the 1-2 shift is only difficult when the car is pulling hard. Try making the shift in the middle of a left turn or going downhill, I'll bet you;ll find it smooth as silk. Also if you shift near the top of the power range, right where the car starts pulling slightly less, smooth as well.

Nik.

I can't find any rhyme nor reason to when the tranny balks going into 2nd... high revs, casual early shift. It doesn't seem to matter. It can be a bit embarrasing when you come away from a stop like a lightning bolt only to be seen rowing around for a gear as people pass by. The thing is that I have been driving a car for years that I can shift smoothly even without using the clutch (NOT normally recommended, but easy to do) and now find myself cringing on a routine shift. The Porsche definitely engages you as a driver. I remember the drive home with it. I live 10 hours from the previous owner and was glad of it, but my shoulders and neck were a bit fatigued after that drive. There is a big difference between modern, cushy sports cars and this classic machine! The tranny will get a rebuild some day and hopefully I can sort this little bugaboo out. Right now I just want to spend some money on gas! Thanks for the responses

"I can't find any rhyme nor reason to when the tranny balks going into 2nd... high revs, casual early shift. It doesn't seem to matter."

This is not normal nor is it classic nor is it only suppose to work on a curve as some have suggested. It sounds like these gearboxes need a rebuild. While the synchros were never a steller performer when the car was new, it was nevertheless effective with the right technique. If you downshift and/or the PO do/did not double-clutch, the synchros (mostly 2nd) wear out and make an idiosyncratic shifter moreso.

Synchromesh on a 915 is something you want to preserve by increasing your skill level as a driver, not a part to wear out faster by shifting it like a HondaToyotaBMWSuburuFord. If you read any of the archived material on this subject, one would come up with only that conclusion.

Sherwood

All of you are whiners! The 915 shifts silky smooth, just don't abuse it. Now try to drive fast with a 901 tranny without destroying it. That takes finesse. ;)

Wow-must be Milwaukee week! I never see fellow WI folk here.

Anyway-now that we're on the subtleties of 915 shifting, sometimes when I shift from 1 to 2 it's just fine-I feel the release of first, the gap between 1 and 2, and then the resistance and sure engagement into 2. Not fast, but sure and no crunch. Other times the release from first is the same but the gap between 1 and 2 seems bigger and the engagement into 2 is waaaay at the bottom and requires a fair amount of pressure. It seems to "click" in at the very end of the travel. It also gives me the impression that it could pop out athough it never does. Still no crunch. What is up with that? I'm hoping shift bushings.

First gear is occasionally hard to engage, but not often. For a stop, I usually clutch, release from whatever gear I'm in and let it lay in neutral, and de-clutch, using the brakes to stop the car-saves synchros and clutch I'm told. If I can't easily slide into 1 I bump 2 and try again. Usually works fine. Unless, of course, there's somebody in a big hurry behing me:).

The chance of this happening increases exponentially if you are at an uphill stop!


You mentioned that you were questioning the bushings on your shift linkage. I did replace mine, but it was easy to tell there was something wrong... in each gear there was way too much shifter freeplay. I could wiggle the shifter front and back and side to side without any pressure being put to the transmission selector rod. A quick check is to look under the cover plate on the floor in front of the rear seats. The shift rod coupler should only have a fraction of a millimeter freeplay fore-aft and rotationally (looks like a small u-joint connecting shift rod to transmission selector rod).
I disconnected the clamp coupling from the shift rod coupler and wiggled the shift rod. Sure enough it was sloppy inside its guide bushing, too. Replacing the shifter ball cup, shift rod bushing and the shift rod coupler is definitely an easy DIY job (and not too expensive for parts, which is saying something for a Porsche!)
Worth looking into if you feel your shifter has what seems like a bit too much sloppiness when IN a gear. It actually shortened the throw of my shifter by an appreciable degree just by tightening things up.;)

Thanks for the info! I'm heading to the garage right now to check.

well I'm confused. :cool:

When I look at the chart, it appears that RPM-difference DOES matter .. . dependent on where in the range you are shifting.

note the orange bars, for example.

http://forums.pelicanparts.com/uploa...1119125265.jpg

. .. of course then there is the timing issue .. . rpm drops faster at higher...

I think he may have meant the following:

Gear ratio charts show the proportional relationship between engine speed and road speed for each gear. The difference in engine RPM when shifting between gears is determined by the gear ratios and is proportional to your current engine speed. For example, if the ratio difference between 3rd and 4th gear is 1.45, then the RPM in the lower gear will always be approximately 1.45 times higher than the RPM in the higher gear at the same road speed.

This means the exact RPM difference increases as road speed increases. If you’re shifting from 4th to 3rd at 3000 RPM, the engine might need to rev to 4350 RPM in 3rd, but if you’re at 4000 RPM, it will need to reach 5800 RPM in 3rd. Knowing this proportional relationship helps you estimate how much to raise engine RPM for a smooth downshift, especially when combined with double-clutching or rev-matching.

So it’s proportional but a fixed proportional value. I find that helpful.

I realize this is a very old thread but though the information on it is useful.

I was told by a man named Zimmerman years ago . Do not shift the 915 like you want to, shift the 915 like it wants you to. I have had great luck with this thinking for 15 years.

+1 for the Zimmerman method, same here. Deliberate shifts. I also double-clutch nearly all downshifts. After spending lots of my own time and $$$$ on rebuilding my gearbox, I treat it with respect.