915 Short Shift Kit?

[jevose]

I have heard differing stories.....Is the 915 short shift kit ok to use on the 915 gear box?? I have heard that it actually makes shifting more difficult and decreases tranny life....What is the verdict??

Thanks,


Jim

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jevose
82 911 SC
88 930 Turbo

[plano25]

I have a rebuilt 915 transmission with a Porsche short shift kit and I don't like it. I think it makes it harder to shift. I am thinking about taking it out.

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Donald Weintraub
1980 Porsche Red 911SC Coupe

[GeorgeK]

Hi Jim,
Here's my take on the subject, based on advice from my racing mechanic: The short shift does exactly that. It SHORTENS the throw on the lever, which is useful for instance if you're short and there's interference between your leg and the lever in 2nd gear.
What it does NOT is quicken the shifts. The synchro rings need time to adapt gear speeds, and if you rush it, no matter which lever you have, you will prematurely wear the rings, and gears.
Once it is clear that the shifts will not be quicker, then it is a worthwile option.
Donald: Yes it makes it harder to shift, because by reducing the throw, you shorten the lever arm. But don't despair, after 1-2K miles the transmission loosens itself. On mine it was so hard to shift into 1st that we almost took it out and apart. It loosened quite nicely in about 500 miles.
GeorgeK

[This message has been edited by GeorgeK (edited 08-22-2001).]

[Jim T]

The short shift DOES speed up the shifting on the box. In other words, given the exact same hand speed, the transmission in a car equipped with a short shift will be forced to shift faster than a car with the stock shifter.

Most people don't slow down their shifting speed after a short shifter is installed. Therefore, their transmission is being shifted 33-40% faster than before.

[GeorgeK]

Jim,
Yes it will shorten the time it takes to shift, and the time to the next overhaul...
You're absolutely right that you instinctively end up shifting quicker, but at the expense of the syncro rings and dog teeth.
I can shift quick enough to force the rings and dog teeth, so a short shift will not bring me much.
GeorgeK

[This message has been edited by GeorgeK (edited 08-22-2001).]

[pbs911]

I have the Weltmeister short shifter kit in my 78SC. I love it. I was tired of hitting the back of my hand on the kneepad and having to reach up to the dash when shifiting into 1st, 3rd and 5th. I'm 6'1 and have positioned the seat even farther back than the factory.

The short shifter does quicken the shift, but at the expense of putting more pressure on the gears themeselves. The same theory applied by using a lever to lift an object. More force is used to move the gears in a shorter distance so wear on the tranny is the necessary result.

As for added difficulty in shifting with hte short shifter, I agree with George. It was difficult to shift into first in the beginning. The shortened "H" patern also took some getting used to. But once the shifter "loosens up" and you get a feel for the shifting pattern, its second nature.

Finally, the P-car is not a quick shifting, off the line, car to begin with. Slamming the gears with the OEM shifter or the short shifter will damage the tranny. I just take care when shifiting and don't rush things. My purpose for installing a short shifter was not to save a 1/10 of a second during shifitng, but was a matter of conviennance. The short shifter serves my purpose well. I'd definatly install it again.



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Paul
78SC Targa

[N11Porsche]

I used to have the Weltmeister short-shift kit in my 1979 911SC. Several years ago, I had to have the tranny completely rebuilt (new syncros, gears, bearings, shift forks, etc.) The shop that did the work is a very highly and often recommened shop in the Bay Area. They recommended that I get rid of the Weltmeister and put in the factory short-shift kit. I was told the Weltmeister shortens the throw too much. This adds leverage and is very hard on the gears & syncros in a 20 year old tranny. I've changed to the factory kit and the transmission is very smooth and the factory kit's throw is almost as short as the Weltmeister kit. Porsche engineered their kit for their car, you figure it's got to be compatable.



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Bill Carcot
1979 911SC
Diablo Region, P.C.A.

[GIBSON]

I've got an 86 911 with the factory option short shift on the 915. The car has 126K miles, no transmission problems whatsoever.
It still shifts as well as a 915 can be expected to shift. I think I'd install the factory kit, treat the transmission with
care and you should be fine.

Bruce Herrmann

[john walker's workshop]

CA-CA!

[GIBSON]

I'm not sure what CA-CA means. If that means you don't agree, that I understand. I'm just listing my experience with 126K miles of factory short shift experience. I've installed several factory units with no problems on other cars. Did the factory install these units to appease the buying public,knowing they were going to shorten the service life of the transmission? Seems unlikely to me, maybe I'm wrong. Just personal experience. I'm no professional wrench so go with what the pros say.

[david c.]

I recently installed the factory short shift kit into my 912E. My car revs quickly and with the 923 ring/pinion, the car needs to be shifted more often than my old 911 3.2. Thus, I was eager to explore the short shift conversion.

One perspective that I didn't see mentioned in the thread was the subjective feel that is altered with the kit.

IMHO, the shifter is more positive and less vague than before. That said, the bushings were all replaced at the same time as the kit was installed. I can't tell you what fraction of the difference in feel is attributable to what alteration.

Nonetheless, I think the car is more pleasureable to drive now. I feel there is merit to the argument that the Porsche designed kit is okay for the box. And, even if gearbox life is shortened marginally, I don't care. It feels better. Porsche parts last a long time. My gearbox has been rebuilt once at about 100k. It's now got 134k on it, give or take. If it goes another 50-60k before rebuild time, I'll be happy.

Later,

Dave

[Early_S_Man]

I think John was referring to that nasty bird material that gets all over my truck when they roost in the overhead trees!

What George said is absolutely true!

If the leverage is reduced, which is how 'the short' part of short-shift kits works ... then there is NO WAY that forces on the internal shift fork are increased by the installation of a kit! The force at the shift knob is INCREASED FOR THE DRIVER, JUST TO ACCOMPLISH A 'NORMAL' SHIFT!!! Thus,sensitivity or 'feel' is reduced, because the reduced travel of the shift knob requires more force than before installation of the kit!

And, shifting a Porsche-design syncronized gear CANNOT be speeded-up by ANY means, except better, closer matching of the engine and drivetrain speeds ... and that is done by eye-hand-foot coordination!!! Just because your hand travels a shorter distance, doesn't mean the shift fork and operating sleeve travels any faster, and certainly not a shorter distance!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[9eleven]

Originally posted by Early_S_Man:

What George said is absolutely true!

If the leverage is reduced, which is how 'the short' part of short-shift kits works ... then there is NO WAY that forces on the internal shift fork are increased by the installation of a kit! The force at the shift knob is INCREASED FOR THE DRIVER, JUST TO ACCOMPLISH A 'NORMAL' SHIFT!!! Thus,sensitivity or 'feel' is reduced, because the reduced travel of the shift knob requires more force than before installation of the kit!

And, shifting a Porsche-design syncronized gear CANNOT be speeded-up by ANY means, except better, closer matching of the engine and drivetrain speeds ... and that is done by eye-hand-foot coordination!!! Just because your hand travels a shorter distance, doesn't mean the shift fork and operating sleeve travels any faster, and certainly not a shorter distance!

I know that you can't disagree with "Early S Man" on this little list (even when he is wrong), but I disagree with the above.

I think Jim is right, if you look at the physics of the short shift kits, if you assume the same hand speed (a reasonable assumption), the transmission will be shifting gears faster with a ss kit than it would with a standard shifter.

And, shifting can be "speeded up." Here's one way to do it. Take 5 seconds shifting from 1 to 2. Then do the same shift in 3 seconds. You have speeded up the shifting in the transmission.

I agree that at some fast speed, it can no longer be forced to shift any faster. But, no one in normal driving shifts the box at its maximum speed capacity.

Therefore, I think that in most instances, the installation of a short shift kit in real life does cause the transmission to shift gears faster than it did before the ss kit was installed.

Just my opinion. Flame away!

PS, I would be interested in hearing JWW's take on this. Why not let us have it, JW?