Problems w/ over 30% reduction short shift ...explanation?

Can anyone provide a simple but detailed explanation on why Porsche does not recommend shifters with over 30-33% shift reduction due to possible damage? I am considering the IMEC shifter which has a reduction of 40% but am thinking about going back to my original selection of B&M so I stay within those tolerances. TIA

I have never heard this Porsche warning. I have a RUF short throw kit set at 50% shorter and experience no problems. Friends of mine have the same setup, same results. What exactly does Porsche warn against?

I imagine the warning has something to do with the fact that with shorter throws, it takes more effort to put the transmission in gear. A short-shift kit is basically like gearing your shifter. Just like on a bicycle, the gear is shorter, but it takes more effort. It can be hard on transmissions if the gearing is really low. The question is whether 33% or 50% is too low. Porsche probably errs on the cautious side.

Mechanically that sounds right. However, the "effort" is being provided by the driver correct? So I'm having trouble seeing how this is "harder" on the transmission. Again I'm confused by this. Anyone else?

Yes, LanceK, I'm confused as well. The increased stress should be with driver effort, not on the transmission. The only way I can think of where a greater than 30% MAY be a problem is that the effort required increases the chances of missed or wrong shifts. This is not a statement of fact or knowledge, mind you. This is pure guessing as to what on earth could possibly be wrong with a greater than 30% reduction.

Try to think of the transmission linkage as having some "play" or room for error built in. When you engage gears, it does place some stress on several internal components. If you change the shift throw, essentially, you're moving the fulcrum point (sorry, going back to my physics days) hence, "sending" more stress towards the internal components. In other words, changing shift throw via any of the short shifters does change the geometry of power transfer from your hand movement to the transmission. By changing the angles, fulcrum and other parameters, you are effectively changing the "power" that gets transferred by the shofter mechanism to the transmission. At the end of this whole cycle, your syncros and gears take most of the brunt. No matter how accurate your shifting may be, your transmission will always shift more smoothly if you apply no more than the necessary strength to move the shifter itself. If you try too hard (and use too much strength), it will actually make a smooth shift more rough. Am I explaining this well?

By the way, just to add to that, I have heard and experienced many dealers who may/will void warranty (VW and Audi, of course) if they see a short shifter of some kind and you complain about a transmission problem. Believe it or not (at least in my personal experience), Porsche seems to be the one company who embrases mods that make sense and don't throw out that "if you modify this, you will lose your warranty" crap. I can see why they would be concerned with too much shifter throw reduction (based on my horribly communicated explanation above).

Alon...somewhat. In that case couldn't you make the argument that if you shift a stock shifter really hard you might theoretically put the same amount of stress as if you shifted a modded shifter softly? I'm no engineer so I need extra help... <img border="0" title="" alt="[Wink]" src="wink.gif" />

I'm with you LanceK, no matter how many fulcrums, parameters, and angle of the dangles you thown in there, the explanation still doesn't make sense. Since the shift kit is the fulcrum, extra pressure there never makes it to the transmission, and if anything, a shorter throw would reduce not increase the force which could be transferred to the transmission. The only possible explanation is that by reducing the throw, you are also reducing the precision by which the business end of the shift mechanism moves and thus may make for more missed shifts or near missed shifts.

I guessing on this but could it be that they are concerned that by shortening the shift, you can make the shift more quickly and potentially beat the syncros on a shift, resulting in misaligned gears and damage. Karl

Karl...intresting point. Are synros "set" or calibrated to a shifter? In other words if Porsche offered a short shift kit for the 996 would the synros be different to work with the different shifter? OR...does Porsche use "slow" synros that necessitate a longer throw shifter? I don't have in depth knowledge of how syncros work so I may be sounding completely foolish.

I could be thinking about this the wrong way but I'm fairly certain that since the shift throw is shorter on the "hand" side, it must be a bit longer on the other side of the pivot point. If it is, it msy be potentially "overextending" the throws at the transmission side. I'm no engineer either but that was my thinking. Who knows. I love my RUF short shifter.

Alon that explanation sounds pretty sound. I'm not still not entirely sure where the potential damage could occur but I think we're getting somewhere. Another way to look at it. If your above point is true. You would think a short shifter would come with a shorter lever therefore gaining a little on the "top" and maybe not needing as much on the "bottom". There was a very recent post here which had a picture of someone who did just that. They cut their stock shift handle for a "poor man's" short shifter. It resulted in a stubby looking shifter.

Oh crap. You're right. I did that once (a long time ago before short shifters were around on an older car). I just cut the shift rod down shorter so I effectively reduced the throw. Still, I have studied what my RUF and my friend's B&M look like compared to stock pieces (2 different approaches at reducing throw) and they both seem to lengthen one side of a "virtual pivot" versus the shortened side. The B&M is longer at the bottom part of the pivot versus the stock shifter. Ithink that at the end of the day, this is not something that is easy to design and many things need to be considered, including reducing left to right movement on some short shifters (my Tanoga shifter for my Audi S4 did that as well as front to back). I'll try to give this much more thought later. I'm going to post something about FVD's power kit and what the camshafts are.

With my installed RUF short throw kit ('01 996 Coupe) set at 50% there is NO additional force needed to shift. I shift as always - like the shift **** is an egg -I'm easy on equipment. The throws are shorter - that's it. I choose the RUF product over the B&M product because the B&M that I tested required more force and IMHO the B&M was a cheap product. I did not want what felt like a Honda S2000 product in my Porsche. (No offense to S2000 owners)

Where's DJ996? He's the one who raised this whole issue when he posted the following statement in another thread: "Also keep in mind the B&M reduces shift throw by 30%, about the same as the GT3RS racing shifters at 33%. Porsche feels any more reduction is hard on the transmission." Hey DJ, can you please clarify? Or Loren, how about you? Inquiring minds want to know! (Especially since I am also considering a short shift kit.) I think I'm leaning towards Alon's idea that you need a little 'play' when your syncros and gears are coming together.

I'm sure that you haven't offended any S2000 owners since most of them know that one of the weakest links on that car happens to be the transmission (and that horrible gauge cluster). Anyhow, I agree that the RUF felt much more factory like versus the B&M which required a lot more effort to shift. I guess that most people are quite happy with their B&Ms but i wouldn't trade my RUF for it. That being said, I'm sure that if you went back to stock, you'd feel a bit of a difference in terms of shift effort no matter how small it would be.

Another thread in the past referred to the potential for faster shifts being the cause for a limit on the amount of throw reduction. Going the same linear speed on the short vs the standard shifter (human side) results in the actuator side (bottom part pushing the cable) going faster by the ratio of the lengths. There just seems to be greater potential for "mashing" or missing. I believe the speed argument. Regarding design, the short shifter does not have a longer throw on the cables. Cables move the same amount. What is different is the pivot point. If you put the normal and short shifter (B&M) side-by-side, you'll notice the pivot point of the B&M is higher relative to the two bearings coming out the fore and aft ends. Awesome shifter but I suppose you CAN get similar results by chopping the stock shift lever! Andy

Have we beaten this to death yet?

Not yet... <img border="0" title="" alt="[Wink]" src="wink.gif" /> Just spoke with a friend of mine who is very technical. He is 98% sure that the "beating the synchros theory" is correct. I really wanted to try out the IMEC shifter to try something different but since it's 40% reduction I think I'll stick with the B&M.

Sorry, I'm not the original source on that info, bobC4S originally posted it back on 5/23/03: "I went with the B&M short ****er because B&M shortens 30 % and you do not have to do anything to the cables except reconnect them. Porsche uses a 33% shorter shifter on GT3Cup cars Porsche feels anymore then that puts excess load pressures on engagement of internal shifter shaft pins & gear fork pins. I got mine from Bobby at Foreign Affiars if you tell him your from Rennlist he only charges you $ 199.00" If you talk to drivers of GT3RS / Cup cars at the track they will tell you it has a short shifter similar in throws to the B%M. Actually as a point of fact, the EVO short shift withthe needle bearings is the closest to the RS shifter.

Maybe someone with a Cup car can clarify this. Karl S??

DJ...Do you know what the needle bearings do for feel?

They're supposed to take out the slop of the stock shifter. I bought a set a long time ago, I may try them with the B&M.

Cool...my friend just bought the EVO shifter but hasn't installed it yet so I don't have any first impressions. So you can change the bearings on the B&M? What does it come with stock?

The B&M comes with aluminum/teflon bushings, with an adjustment screw on one bushing, much better than the cheap plastic oem units. Even better, IMO, are the EVO true needle bearings which are intended for use in the stock shifter. They look exactly like an old universal joint bearing off a driveshaft if you have ever worked on older cars. They require no adjustment screw. I'm going to try them on my B&M shifter to see if they can be used, I'll post results soon. Looking at them, I see no reason they could not be used for this application. Let us hear how your friend likes the EVO shifter. Maybe the best setup would be a B&M shifter morphed with the EVO bearings.

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Karl S: <strong>I guessing on this but could it be that they are concerned that by shortening the shift, you can make the shift more quickly and potentially beat the syncros on a shift, resulting in misaligned gears and damage. Karl</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Bingo! Karl hit the issue right on the money. The geometry of these ultra-short shifters moves the transmission internals too quickly. All this does is accelerate wear on the syncro's, operating sleeves, and in some cases, shift forks. IMHO, this is another case where "Less is More".

Steve, are you saying short shifters are not a good idea on the 996? If not, which short shift would you recommend for the 996? TIA

Hi Doug: LOL,.....All I am saying is that the short shifters that reduce throw more than Porsche's recommendations will really accelerate wear on the transmission's internals. Given that Porsche does not sell or offer any pieces for the 996 tranny yet, rebuilding one is not possible and one would simply have to exchange it for a new one. I've not had any opportunity to take one apart yet, but I'd hazard a guess that they are using the same type of soft brass syncros as found in the 993 tranny's and these were not known for longevity. I think the EVO or B&M ones are OK.

Thanks Steve, your input is always appreciated. What would be a symptom of the synchros/internals not being ready for a shift? For example a couple of times last weekend at TWS coming into turn 2 going from 4th to 3rd,I would rev match and...nothing - like the shifter has hit a wall. Then I try again and it goes right in. Didn't happen every time just a couple of times, I figured my rev matching and shift wasn't just right. Could this be a symptom of the synchros not being "ready"??

Hi Doug: In most cases, the Borg-Warner type syncromesh in these tranny's will try to grab the operating sleeve and make the shift. The sharp points on the syncro teeth and/or operating sleeve teeth become blunted when the RPM of the gearsets do not match well and one simply pulls on the shifter a bit harder. Over time, the little teeth in there get rounded off and take longer to engage so you get a "graunch" or a catch when rushing a shift. In a worst case scenario, one would just have to shift it like a 915,.... Its really hard to tell for sure what was going on at TWS with your gearbox, and you might have simply hit the gate between slots in the pattern. When the adrenaline is flowing, its hard to tell sometimes,... A shifter out of adjustment will do the same thing and I'd not rush to any conclusions about the health of the transmission.

Steve, Thanks, I think that's exactly what happened, I hit the gate in the pattern, I never heard any noise from the gearbox. As I suspected, my shifter needed a slight adjustment,I had too much "slop" dialed into the B&M, I tightened it up a bit and now it feels better.