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by: Croc'ed

Description: Guard Transmission’s “987 Club” Limited Slip Differential InstallationIntroductionHello to my fellow Porsche enthusiasts! For the past 3 seasons, I’ve been driving my 2007 2.7L/5-speed equipped Cayman at various PCA-sanctioned driver education (DE) events throughout the northeast USA. What a thrill it has been for me, to learn what a marvelous machine Porsche has built! As I’ve progressed within the PCA DE ranks to the black (advanced) driver’s group, I’ve steadily modified my vehicle with the goal of improving its track-worthiness without completely sacrificing its road-worthiness. I like to think of it as my own personal Cayman R/T specification. You may peruse a list of my modifications, to date, in the Planet 9 garage. The Planet 9 community’s body of knowledge has been an invaluable resource to help me decide which modifications to perform, and how to install them.One modification that piqued my interest was adding some form of limited-slip differential, as this option was not offered from Porsche when I ordered my car in November of 2006. I read as many of the LSD/TBD threads and installation articles as I could find. For a good overview of differential types and their operation, I suggest reading Race Car Vehicle Dynamics by William F. Milliken and Douglas L. Milliken, Section 20.2 “Differentials,” available from SAE International (order number R-146.) I decided that a TBD unit would be the right choice for me, but neither Quaife nor Guard Transmission offers a TBD for my car. Guard Transmission does produce a LSD for my vehicle, so when the opportunity came to bid on one at a Planet 9 Insider’s auction, I took the plunge and won the auction. Guard Transmission offers several different versions of their LSD, depending on the intended application. Since I spend a lot of time driving on the track, using R-compound tires, I selected their “987 Club” 45/65 model.
I decided to install the differential by myself, at home in my driveway. I worked with the rear tires of the car supported on ramps, and with the gearbox in the car. If I had to do it over again, I would reconsider this choice. The extra time required to remove and replace the gearbox, given the advantage of working on the bench instead of lying on my back, would have been time well spent!I should note here that I used to make my living as an auto mechanic before completing a degree in mechanical engineering. While this installation is not rocket science, the attributes of patience, cleanliness and attention to detail, along with a “feel” for mechanical installations, the proper tools, and access to professional help/information are all prerequisites for success. Some of the techniques described herein are “workarounds” using hand tools and measurements that are available to a “shade tree” mechanic in lieu of more “professional” tools and techniques. Removal and InstallationPlease refer to the following previously published article and thread for a couple of thorough descriptions of a similar Quaife TBD installation:• K-Man S’ article: LSD / TBD limited slip differential - Articles• Drew @FCM’s’ thread: http://www.planet-9.com/u-s-northeast-noreasters-region/31821-atb-install-pics-tech-pricing.htmlFor further detail, please refer to your local Porsche dealer and ask to peruse the following documents:• PET catalog, sorted by your car’s VIN, showing the differential parts in an exploded view and listing all part numbers • Boxster service manual 39 09 19, Removing and installing the differential (transmission G 86)For this article, I will only add commentary where necessary to either highlight differences unique to the 5-speed gearbox, or to add further detail.On the Workbench - Disassembly I chose to replace all bearings, races and seals, and to use new ring gear bolts and stub axle retaining clips.Use an adjustable two-jaw puller to remove the bearings from the differential carrier. Heat the old bearings using the “blue wrench” (aka propane torch) to facilitate this operation. Loosen all the ring gear bolts a few turns each, heat the ring gear using the “blue wrench,” and gently tap on the bolt heads in an alternating circular pattern to “walk” the ring gear off the carrier.Note the insertion depth of the stub axle shaft oil seals in the side cover and the gearbox housing, respectively, before prying them out.Use a hammer and punch to gently “walk” the outer bearing races from their respective bores, working from the outside in. The bearing shims will fall out from behind the outer races. Keep these shims for future reference and possible reinstallation.Thoroughly clean and dry all of the re-usable parts, threads included. Use gasket preparation solvent and plenty of clean cotton rags.
Measurements The three critical measurements used when setting up a differential are: pinion gear depth, gear backlash, and bearing preload. In this case, we are changing only the differential carrier, so the pinion gear depth is not adjusted. To replicate the gear backlash and bearing preload of the factory setup, we need to record two “comparative” measurements of the old and new differential carriers. Any differences noted between the two units will require adding to, or subtracting from, the original shim thicknesses. Porsche supplies shims in varying thicknesses, in increments of 0.04 mm (or 0.0015”.)
• Dimension “B” (for backlash) measures the distance from the ring gear mounting face to the back face of the inner bearing race, nearest to the side cover. The intent is to position the ring gear mounting face (relative to the side cover) exactly where it was before the operation. For example, if dimension “B” on the new unit measures 0.001” longer than the original, you’d need to reduce the side cover’s shim thickness by 0.001”, and vice versa.Note: Any changes to this shim will need to be accounted for in the gearbox side bearing’s shim. More on this later…• Dimension “P” (for preload) measures the distance between the back faces of both of the inner bearing races. The intent is to preload or “squeeze” the bearings, exactly as much as the factory had done. Using the previous example, if dimension “P” on the new unit measures identically to the original, you might be tempted to think you could re-use the original shim, but you’d be incorrect! Since we reduced the shim thickness on the side cover’s bearing by 0.001”, we need to add it back to the shim behind the gearbox side’s bearing to maintain the same preload. So, we would increase the gearbox housing side’s bearing shim thickness by 0.001.”I enlisted the services of a local machine shop to obtain these measurements using a very large, dial-type Vernier caliper that measured to the nearest 1/1,000th of an inch. Fortunately for me, the two units measured identically (each measurement was taken at three different places around the circumference,) so I was able to re-use the original shims without modification. Thank you, Guard!ReassemblyNote: To facilitate installation, chill the outer bearing races and the new differential carrier by placing them in a freezer. Heat the ring gear and tapered roller bearings by placing them in an oven at 212 degrees F.Lightly lubricate the inside diameter surface of the ring gear using new differential oil. Apply red thread locking compound to the new crown gear bolt threads, and tighten the bolts in an alternating circular pattern to gently “walk” the ring gear onto the differential carrier. Torque bolts in two stages as described in the literature.Lightly lubricate the inside diameter surface of the new bearings using new differential oil. Gently “walk” the bearings onto the differential carrier using a hammer and collar until the bearing seats firmly against the machined land on the differential. Listen for a solid, high-pitched, “pinging” sound all around, and check that no light is visible between the inner race and the machined land, to insure the bearings are completely seated. [Hint: I used the inner race from each removed bearing as a collar. Cut away the bearing cage using diagonal cutting pliers and all the roller bearings will fall out. Dress the inside diameter of the inner race with a rotary file so it doesn’t wedge on the differential shaft. Reverse the direction of the collar on the shaft so the old and new inner bearing races are facing each other. Use a length of pipe if necessary to clear the differential shaft.] Note: The PET catalog called for a part called a “drive wheel without function-drive” (or “speedometer drive wheel”) to be installed between the differential and the LH tapered roller bearing, but this part was not used on my car.
Lightly lubricate the outside diameter surfaces of the new outer bearing races using new differential oil. Install the proper shims, then gently “walk” the outer races into the bores on the side cover and the gearbox housing, respectively, using a hammer and collar until the outer race seat firmly. Listen for a solid, high-pitched, “pinging” sound all the way around, to insure the races are completely seated. [Hint: I used the removed outer races as collars. Reverse the direction of the collars so the old and new outer races are facing each other.] Note: installing the outer race in the gearbox housing is much easier with the gearbox sitting on a workbench, or with the car on a lift!Lightly lubricate the inside diameter surface of the new stub axle shaft oil seals using new differential oil. Gently “press” the seals into the bores on the side cover and the gearbox housing, respectively, using a hammer and collar, to the depth noted prior to removing the original seals.
Lightly lubricate the ring and pinion gears, and both new tapered roller bearings, using new differential oil. Install the differential and side cover as described in the literature, using blue thread locking compound on the side cover bolt threads. Note: The large diameter O-Ring was not used to seal the side cover to the gearbox housing in my car. Instead, form-in-place gasket compound was used by the factory. No provision was made to accept this O-ring, so the PET catalog was incorrect in this case.Remove and replace the stub axle retaining clip at the end of each stub axle shaft. Be ready to catch the clip as you remove it, as it is spring loaded and can unexpectedly take flight when unloaded. Don’t ask me how I know this! Note: Each stub axle on my car contained a pair of roller bearings and a spacer, retained by a second, smaller circlip. These bearings prevented the stub axles from fitting into the new LSD. After a few phone calls between Paul Guard, Matt Monson and myself, I was assured that these bearings needed to be removed. Apparently, these stub axle bearings are remnants from an older Boxster design that do not appear on the Cayman S’ 6-speed gearbox.
Install the stub axles into the gearbox using a mallet. Good luck doing this on your back with the car supported on ramps! There was no way I could get enough of a swing arc to create enough force, so I jury-rigged a screw jack against the outer sub-frame, using a 1-foot length of 2x3 as a beam across the sub-frame to form a base for the jack, and slowly “pressed” the axles into place. This took all of a few minutes, after dickering with a mallet for longer than an hour.The rest of the installation is straightforward and needs no further clarification.Driving ImpressionsI was a bit concerned that the car would make ungainly noises during turns, would under-steer noticeably, and that I’d need to re-learn how to drive the car on the track. So, I drove 500 miles one-way to VIR on my stock tires (PS2s) to “shake it out.”I was impressed by its benign nature, as I only noticed any clicking noises during slow, tight parking lot maneuvers. I can only surmise that the drive wheels remained locked together for the bulk of my normal street driving, without detriment to the car’s usual dynamics. I’m sure that I’d notice a difference in slippery conditions; however I did not experience any such opportunity at the time.Swapping to R-compound track tires (NT-01s) at VIR, I drove conservatively until I could develop a feel for any subtle dynamic differences. Once I felt comfortable and picked up the pace, I noticed that the car was much more stable under heavy braking. As I pressed harder, I had to remind myself not to forget the good habit of getting the car in a straight line before initiating braking, since the car felt stable even when I didn’t! Another benefit was the ability to get on the power sooner in the turns, exiting with confidence. I enjoyed the way I could now brake hard and downshift to 2nd going into Oak Tree turn (the tightest RH turn on the course, leading onto the longest straight,) flick the steering wheel to rotate the back end of the car, stand on the throttle and plant my right side tires on the curbing at the apex, without feeling that I might run out of track at the exit. The result: an additional 6 MPH at the end of the back straight! I suppose I did need to re-learn how to drive the car on the track…faster!Driving home on street tires, I was once again impressed with the “transparent” nature of this modification. After 1,000 street miles and a few hundred track miles with no unusual noises or negative driving impressions, I’m declaring this installation a success.I’d categorize this modification as an option that should have been available from the factory, and as a must-have option for the track. Installing Guard Transmission’s “987 Club” 45/65 LSD in my Cayman has transformed the car for the better. I now feel that I’m driving the car as it was meant to be driven. This product gets a “double thumbs up” in my book! Contact Matt Monson at Guard Transmission ([email protected]) and tell him you read this article on Planet-9.com if you think a Guard LSD might work for you, too. He’ll set you up with the proper version for your particular application (street only, road and track, or track only.)CreditsI’ve been very fortunate to have had the help of many good people to bring this project from idea to completion. While I’ve surely overlooked some, I’d like to give credit where it’s due and express my appreciation to the following individuals:• Planet 9 – Ken Smiley, Gator Bite, Drew @ FCM, Bill C, Pistol Pete, jonathan, glenn, etc.• Guard Transmission – Paul Guard, Matt Monson• Porsche of Huntington – Mike Ronan, Thom Moehringer, Kamil Olszewski, Nadim Khalek, Russ Devodier• Fairfield County Motorsports – Drew Wikstrom, Jim Reilly• TPC - Mike Levitas• Flying Lizard Motorsports - Johannes Van Overbeek• Woerner Engineering – Bill Woerner

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