Short Shift Bad For Rebuilt 915?
 

Just had a rebuilt 915 installed in my car, and my mechanic frowned upon my desire to install a factory short shift kit...his logic being that after a few thousand miles the trans would be 'broken in', and then potentially ready for the additional strain that the short shift kit places on the transmission. Is this true? I don't see how, shifting with normal effort in everyday driving, a short shift kit would be more taxing on the tranny. Any thoughts?

Thanks...

http://www.pca.org/tech/tech_qa_area.asp?id=7&classification=Transmission& startat=26

Short shifters are harder on the synchros. Your mechanic might be worried about you shifting too fast; i.e. if you forget that your throw is shorter.

the fact that the lever below the pivot point is longer, makes the shift sleeve move over the friction syncro ring faster than the factory designed it to. this happens with you shifting it no differently or faster than normal on the shift knob end. it basically doesn't give the syncro assembly quite as much time to match gear speeds for a smooth shift. i don't like them either, whether on my rebuild jobs or just normal driving. they just feel kind of wrong.

That is EXACTLY what he said as we discussed it (and he made the appropriately screwed-up funny face at the same time :D)

Thanks for the confirmation...

Maybe a stupid question, but why then did the factory offer these?

Todd

For transmission life, I'm not a huge fan of them. That said, I have one in my 1972 RS clone, simply because the transmission throw seemed so large in that car. The short shift kit was installed (if I recall correctly) on all of the 915 Carrera cars straight from the factory, so it is a factory-approved part. The installation of the kit reduces your shifting precision, if you shift slowly (as I usually do), and ease the gears into their position, waiting for the synchros to mesh, then it shouldn't make too much of a difference. But if you slam gears together, it will indeed put more wear on the transmission.

-Wayne

Do the Rennshift or Wevo shifters treat the synchros any better than the factory short shifter?

I've got the factory short shifter in my track car and a standard shifter in the other. I love the throw on the SS but it definately feels harder on the 1-2 shift than the other car. The tranny is rebuilt on the track car and I don't want to put undue strain on it.

I fixed my link. Click on short shifter from the list (the first question).

http://www.pca.org/tech/tech_qa_area.asp?id=7&classification=Transmission& startat=26

I have put the original type shifter back in race cars as the drivers did not like the Porsche short shift "feel"

I love the "feel" of the short shifter and also have a Seine gate shift kit in the car. Makes for a very precise experience vs. stock. But, it makes the shift into second on this tranny more difficult and it's a rebuilt unit done by Chris Powell who is referenced on the PCA link. I spent a ton of time getting it adjusted right.

Britwrench drove my car when I had the PPI done, before I swapped over the shifter which was previously in my other SC. I'm either going to the WEVO or will put the standard shifter in and retain the Seine kit. I've missed the 3-2 shift not wanting to force it a couple times in this car on the track at Pacific Raceways last summer going down a steep hill and had to take the escape road :-)

Yeah, with my stock 915 I usually skip second gear ;).

the other thing the SS does is increase the effort required to shift. standard physics. the fulcrum principle. there is another way out, but you probably would laugh. sure shifts nice though.
http://forums.pelicanparts.com/porsche-911-technical-forum/240038-amazing-long-shifter.html?highlight=long+shifter

I want that link O_O.

Wayne...Are you saying my 1986 Carrera has the factory SS fitted already?
 

I was considering a SS for my 86 but from what you are saying it will already have one as standard equipment from the factory?
How do I check?

I thought the 85 or 86 and on had a shorter shifter installed, but that a short shifter would still remove about 10%. Before then it was something like 25%. (I could be blowing wind out my ass... can't remember where I read this).

I had a short-shift kit in my 74 for a while and got rid of it again for two reasons: One, it developed a terrible rattle because the lever ball was not fully extending into the cup of the shift rod. I believe mine wasn't the factory design but the Weltmeister design if I remember correctly. I tried everything and finally out of frustration yanked it out. The other reason is that it didn't quite feel right. I actually like the longer throw of the stock shifter.

MikeK has the Wevo gate shifter that also has a much shorter throw plus the gating. It is a nice piece of engineering. But again even if the price wasn't that high I'd still prefer the stock shifter. It simply "feels" period-correct.

Basically, the standard shifter in 1985 and 1986 had a 10% shorter throw than the shifters up to that point. The bend in the lever was also a little different. A short throw shifter was optional from 1985 that gave throws 25% shorter than the original '73-'84 shifters and approximately 15% shorter than the standard shifter of the same year.

JR

Yeah, my ass was flappin a bit.

I know what ya mean ischmitz :). I'm just going to install a shift gate.

By chance, does anyone know what this is:

http://www.***************/productpage.aspx?cid=21&sid=302&pid=105168

?

That kit was/is manufactured by Target, an equivalent of a WM short shift. The new ball section replaces the lower portion of the factory shift lever (it's only glued together). The aluminum block spaces the shift tube downward an amount equivalent to the increased distance below the lever pivot point so the shift assembly doesn't bind. The WM accomplishes the same effect by instead positioning the shift housing higher an equivalent amount.

At a claimed throw reduction of 40%, it's about the same as the WM unit @ 39%, so it provides the same loss of leverage and the same notchier feel compared to the stock or the factory short shifter (0 and 25%, respectively).

I suggest using either the regular or the factory short shifter and to not rush the shifts between gears. I also recommend double-clutching along with whatever type of shift lever system used.

Sherwood

That's Mike"Z" ya dumkopf....anyways, a 915 is NOT designed for fast shifting. Even though I have a short throw, I shift slowly. I remember how much my rebuild cost....:eek:

I've always been advised to stay away from short shifters and to go with the factory kit if I must have one (for the above stated reasons regarding synchro abuse).

I ended up putting the WEVO shifter on my 915 and I like the kinda "rifle bolt" feel of it. I didn't really dislike my VW bus-like stock shifter at all, just had the chance to buy a used WEVO and, having read all the great press about it, decided to try it.

It's definitely a shorter shift than stock but I don't notice a great deal more effort to shift it. I still respectfully let the synchros do their job without rushing them (I don't shift it any faster than I did with the original shifter).

I don't feel it's any "improvement" as far as getting the job done (doesn't do anything to the trans to "allow" it to shift quicker or more precisely - but I can see how it might invite abusive synchro forcing in some hands). But, liking the feel of it, I wouldn't go back to the old shifter.

When I put the shifter in I also went with WEVO trans/engine mounts and coupler, all of which add up to a package that feels quite a bit more all of a piece.

Just how quickly one shifts, a clean, rev-matched, low-force shift, is dependent on how quickly the rev's fall. --generally slower when putting around town, and faster when dropping off redline.

Also, the shorter the throw, then the less feel for the syncro matching you have. The wevo is VERY short. Not much in the way of "precision" IMO ... it just blows thru the syncro engagement. I suppose that makes it feel more binary - no 'in between.' a lot of people like that.

..

It sounds silly, but the the thing I did a few months ago after reading a post on here that really improved the feel of the shifter and ease in finding gears was to add a large spring I got at Autozone to the shift lever. Now when I take it out of second the spring pulls the lever over and I move it straight up and right into 3rd and straight down to 4th. I have the stock shifter and was considering one of the other options, but now I'm not. I have to admit I was really surprised how much this $3 change helped.

Best advice I ever got when buying my first 911 was, "never apply more force to the shifter than you would to a raw egg". Fingertips only. People who shift with their whole fist don't drive my cars...they're welcome to the Mustang 'vert though.

Previous threads on this subject seemed to contain lots of positive comments on the Wevo product. It retails for $595.00 but most everyone who has one seems to comment favorably. Anyone have a Wevo?

You might want to look at my posts on this thread - doh! :D

What decel thingy?

Below is from earlier thread - hope it helps (mine is disconnected and it neither smokes nor pops - just drops revs MUCH faster. Has to be connected for a smog cert. though):

"If you have your decel valve (vacuum limiter) connected, pull the vacuum line off of the decel valve nipple and plug with a golf tee. If that solves the problem then you need to fix/replace your decel valve or leave it unplugged. You can fix by pulling it out and squeezing it slightly in a vice (search on "decel valve vice").

The decel valve is located towards the right rear of the engine (rear = toward firewall). A bad decel valve will cause your idle to "float" - you come to a stop and the idle slowly begins to increase. When working correctly, the decel valve prevents rapid rpm drops in between shifts - it also prevents popping, smoking, on rapid deceleration.

BTW ... I have an 82 SC and it DOES have a decel valve."
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Does this apply only to CIS cars, or will my 84 Carrera/Motronic have one of these? I've always wondered why the idle falls so quickly between shifts... just thought it was light flywheel.

the 3.2 has a decel valve in effect. it's the idle control valve. different than the CIS style entirely. all computer controlled. it opens just as the idle drops and grabs and controls the idle speed in one fell swoop. idle comes down and whoomp, stable.

Like, that's a GOOD thing, yes? :)

Ok, thanks JWW... I've cleaned my ICV with alcohol and my idle is pretty stable, but my heel-toe blipping seems fruitless since the revs drop off so fast.

The 915 downshift from 3-2 is so slow for me that if I heel-toe/blip, by the time I'm getting into 2nd, the revs are down at idle.

Do I need to blip higher or longer? Or is double-declutching my best bet?

Sorry for the highjack, but this is without the short shift kit and my 84 has the longest shift of any Carrera, since they dropped it in '85.

"...Do I need to blip higher or longer? Or is double-declutching my best bet?
..."

The speed difference between gears is greatest when the vehicle is at speed and the gearbox input shaft is idle (clutch disengaged), thus the most wear will be on the synchros at this point.

Rev-matching (blipping the gas in neutral) only matches the rotational speed of the flywheel (engine) and clutch disc (gearbox input shaft); it has nothing at all to do with the synchros. You must double-clutch (downshift) to relieve the synchros of speed matching duties and subsequent wear.

Sherwood

[quote=911pcars;3632594You must double-clutch (downshift) to relieve the synchros of speed matching duties and subsequent wear.[/quote]

And if spot on (which is rare, no matter how good you get at it) NO force at all is necessary - the lever just goes there as fast as you care to chance that you've sufficently matched revs. Nice feeling, akin to finding the sweet spot hitting a tennis or golf ball - but much more expensive if you miss! :D

"The 915 downshift from 3-2 is so slow for me that if I heel-toe/blip, by the time I'm getting into 2nd, the revs are down at idle.

Do I need to blip higher or longer? Or is double-declutching my best bet?"

I forgot to answer the first part of your question earlier.

If the downshift is completed (in a gear) but the engine speed drops, disengage the clutch and blip the throttle to match the engine speed to the same rotational speed the input shaft would be in that gear, then engage the clutch. That would be equivalent to an extended double-clutch. Speed match gearbox internals; speed match flywheel and clutch = smooth downshift with no drama.

Blipping the throttle is often needed to complete the second part of a double-clutch downshift, when the gear change isn't fast enough to complete during the rev in neutral and clutch engaged.

Probably better demo'd than explained (at least my explanation attempt):
Here's an explanation, but average visual display:
http://youtube.com/watch?v=jAvOOLYPmMM&feature=related

another at speed (RHD)
http://youtube.com/watch?v=WD5zq0Jkpoo

and a little faster (LHD):
http://youtube.com/watch?v=0j-3xIZK-Bk&feature=related

Sherwood