Project R35 GT-R, What is inside our 1200 lb/ft Capable GR-6 Transmission!

For years I have wanted a transmission built by Sheptrans, builder of some of the most amazing transmissions for AWD Mitsubishis and Nissans but I never had a car worthy of one of these pieces of automotive art. John Sheppard, the owner of Sheptrans has established himself as the builder for the Nissan GR-6 dual-clutch transmission.  Sheptrans is the company behind some of the fastest, most powerful R35 GT-Rs in the world.

The R35 GT-R has the unfortunate reputation for being a transmission destroyer as it was notorious for being so in its first year of production, however, Nissan has come a long way with programing changes and updates to the transmission itself.  The stock transmission is now pretty bombproof in the stock car and can even handle about mid-600 hp power levels without an issue.  Add sticky tires and more power though and it’s pretty easy for this heavy and powerful car to make the transmission go boom. Adding to the problem is Nissan does not sell service parts for the GR-6.  The only part available is the pan gasket.  You cannot even get replacement filters from Nissan!

Now our goal for project R35 isn’t to build the fastest GT-R ever, or set power records.  We do want to build a very well-engineered car that is powerful, does not have annoying driveability issues, and has the ability to smash million-dollar exotics.  Our engine will hopefully be able to generate about 1100 hp and 900 plus lb-feet of torque with more flexibility and less turbo lag than stock.  We want to be able to run high 9’s/low 10s on street tires, just drive to the track, run and drive home, no slicks or DOT drag tires. Our top speed goal is 200 mph and to do a decent lap time around a road course without tons of aero or super-soft cheater tires.

Now our stock trans is in no way up to this so we finally saved our money and had Sheptrans build our transmission into a Stage 4 Plus Extreme transmission build. Our transmission is rated for 1200 lb/ft of torque and has upgrades to take the most punishing drag strip launches. This is the single most expensive single car part we have ever purchased but it is worth every dollar!  We were involved in setting up some of the fastest GT-Rs in the country 9 years ago and we discovered some of the issues that were present in the most built transmissions of that time.  Much has been learned since then and Sheptrans has countermeasures for every single thing we ever experienced with these transmissions with severe use and high horsepower.

Sheptrans uses a lot of parts manufactured by Dodson Motorsports.  Dodson is a NewZealand based company that is the premier manufacturer of heavy-duty motorsports parts for many dual-clutch transmissions.  The bases of our build revolves around the Dodson Extreme gearset.  The extreme gear set is designed to handle over 1500 hp and is their current top-of-the-line gearset. The gears are 30% wider and made of a much stronger secret alloy.  The gears have a modified helix angle for greater strength, in fact, some of the gears look almost straight cut.  The gears are precision cut, then ground to final size.  Last the gears are superfinished for superior fatigue strength and less friction. Our gearset came with heavy-duty input and output shafts, shift forks, shift rods, and parking pawl.

A GR-6 transmission uses a multi-plate wet dual-clutch system.  Ours is replaced with Dodsons billet alloy Promax 10 disc clutch. The clutches use 10 Exedy discs for each section of the dual-clutch. This is up from the factory 6 discs. Sheptrans has an 11-disc option but John Sheppard recommended against it for our power level saying that it had a significant reduction in smoothness and we didn’t need it.

The factory clutch baskets are known to break from heavy loading and the Dodson baskets are one-piece billet parts vs the thin stamped and welded sheet metal stock parts.  This is many times stronger than stock and should not ever break.  The clutch assembly has a heavy-duty clutch return spring clip and improved higher temperature seals for the forged alloy pistons and piston shafts.

6 comments

  1. Are you sure you want to add “super-strong ARP bolts” in the blind holes machined in to the cast aluminum differential cover? Higher strength bolts means more clamp load to achieve the same stretch which in turns leads to shearing the threads in the non-serviceable transaxle. Those holes don’t look to deep so it would be a good idea to triple check the thread engagement calculations.

  2. Is there some reason that they don’t go with straight cut gears? Seems like noise and vibration wouldn’t be a serious consideration in this application.

    Personally, I kind of enjoy a bit of gear whine in a race car.

    1. The helix of the gears is changed for more strength. Helix gears can be stronger although they do waste more power.

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