I've been asked for years to produce a shifter for the 930 4-speed.  Seems like a simple thing - after all, the shifter is basically the same as the 915 shifter, right?

Well, not quite, unfortunately.  Although many of the same parts are used for both variations from the factory, there are enough differences in the design to make a visit back to the drawing board a necessity. 

The first issue to be addressed was the difference in lever ratio.  The stock 915 shifter has the same lever ratio for moving the shifter side-to-side (along the neutral plane) as it does moving forward and back (into and out of gear).  That is, the pivot point is at the same height for all motion.  The factory 930 shifter retains the same left and right ratio as the 915, but has a much reduced ratio (about 30%) for the fore and aft direction.  The shifter is built like a 915 short shifter for into-gear movement but has a conventional ratio for the side motion.

With the RennShift design, we prefer not to reduce the side-to-side motion much, while reducing the into-gear distance. As the pivot point for the two directions becomes further separated, a large lateral displacement of the pivot carrier occurs.  This encroaches on the bias springs and we run out of room!  The factory was able to use the same housing for 915 and 930 because of the large diameter used in their design.  One of my design requirements when I created the RennShift was to fit it into early cars with minimal intrusion.  I wanted as little enlargement to the hole in the carpet as possible, and I wanted the shifter to fit in the center console of a 914.

There were enough requests for a 930 version of the shifter over the years that I continued to work on the problem in the back of my mind.  The development progressed over a few years in baby steps.  First, with low expectations I tried further overall reduction of the RennShift with the 930 transmission.  With the fore-aft in the appropriate range, the side-to-side motion was ridiculously short - not an option, as assumed.

So, I decided to look at it a little differently.  I did not want to modify the main housing of the RennShift, as the commonality of the modular design is what allows me to offer an entire new shifter for the price others charge for just upgrade parts.  So, I took a look at rest of the system.  Lengthening the cup receiver at the head of the shift rod would increase the sideways shift throw (since the shift rod pivots in that direction), but would have no affect on the fore-aft since it is straight linear motion of the rod.  This turned out to be the perfect solution.

After performing a few trivial calculations I made some aluminum chips with my lathe and mill, fused some metal with the welder, and made created a dusty mess making MDF spacers.  The mock-up parts were mated to a car and functioned beautifully.  With the RennShift's adjustable throw and different available stick lengths, a perfect range of throw was realized from the care-free long shift lever with 20% throw reduction down to the sporty feel of the shortest ratio combination - stock lever length with 33% reduction.  Long lever with 33% and stock lever with 20% fill in the middle of the range.

Just one more item needed to be addressed before creating a drivable prototype - the spring bias.  Looking at the shift pattern, it seems that there should not need to be any change from the 5-speed design - let the shifter rest in 1-2 and push against a spring to enter 3-4.  In practice, this is not acceptable - it is a bizarre feeling to drive a 4-speed pattern with the shifter forced to the 1-2 gate.  The natural motion is to pull the shifter against a spring to the 1-2 gate, as is common to any shifter with a spring bias, whether 4, 5, or 6 speed.  Actually, it's the spring out of low gear that seems to engage muscle memory, as I can go between a 3-speed, 4-speed, dogleg 5-speed, common 5-speed, or 6-speed and all feel natural with a bias spring away from 1st gear.  For those of you who have been around a little longer or are more automotively diverse; even 3-on-the-tree is spring loaded away from the 1st gear gate.  So, the spring mechanism is not a direct swap, but it is an easy modification with the RennShift design.

Next, a small run of the real working product was created.  With completion of customer evaluation and design for ease and efficiency of production, the parts were produced in quantity.  For the 930 shifter we ended up with 5 unique parts and an improved base-plate.  This base-plate is now used on all of our 911 shifters and affords even quicker installation of an already simple to fit product. 

See the product page here: http://www.jwesteng.com/shop/index.php?id_product=52&controller=product