Building the Bulletproof Transmission, Secrets of the Pros

WPC treatment leaves a hard, smooth lustrous surface on the gears.  WPC reduces heat and friction, saving power and greatly increases the strength of a part.  It also aids the syncros, helping them grip better, thereby smoothing and speeding shifting.

Finally we finish the gears with WPC Processing. For details on how WPC works check Here!

WPC is a Japanese process where the parts are hit with very small, very hard spherical ceramic and metallic dry lubricant elements at ultra high speeds.  WPC leaves a very fine, hard, wear resistant and low friction surface finish which has superior grain refinement and development of compressive stress at a shallower depth when compared to shotpeening, of about one thousands of an inch.  WPC can also be applied to delicate parts and gets easily to the bottom of gear teeth and shaft spline roots.  WPC greatly reduces friction and heat build up which is often a problem in cars driven on road courses and reduces power loss through the drive train.  WPC can also be applied to delicate parts of a transmission like syncros without harming them.  WPC has no negative side effects and greatly strengthens, increases life and reduces friction on parts.  WPC usually also results in a 100% or greater improvement in fatigue strength with improvements in surface hardness and tensile strength as well.

A closer view of WPC treated gears shows the lustrous finish imparted on the parts. WPC helps strengthen the shafts even in the area of the splines.

With our test transmission pictured here, we used the WPC process on the gears, shafts, shift forks, sift fork shafts, shift mechanisms, syncros (where it helps syncros grip, smoothing and speeding shifts) and on the plates of our transmissions limited slip differential where it makes the differential action smoother and causes the LSD to create less heat.  Finally we WPC treated our transmission case.  This helps stiffen the case and makes it less likely to flex, yield and stretch.  This flexing of the case causes the gears to spread apart under load to where the gears don’t mesh correctly weakening them. 

We WPC treated the shift shafts, shift forks and the shifter mechanism.  This greatly smoothed the shifting action and strengthened the wear and failure prone shift forks.

WPC treatment of the transmission case stiffens it and prevents the case from stretching.  This helps keep the gears in mesh.  The gears pulling apart really can cause them to fail.  WPC can be applied directly on all surfaces of the case, even in bearing and seal areas.

Some other tricks we used were to use a 1998 and later case.  This case has heavy ribbing which also helps prevent case flex and gear spread.  The ribbing also helps keep the transmission cool.  We used a Nismo 4 Pinion mechanical limited slip differential to replace the wimpy stock 2 pinion viscous limited slip.  The Nissan limited slip is a one way mechanical Salisbury differential that uses the wedging action of the pinion shafts to increase the clamp load on the clutch plate.  The more differential tire slip happens, the harder the differential locks up.  The Nismo diff locks up many times harder than the stock viscous diff. The one way action means that when the car is coasting with no load on the drivetrain, the differential is completely unlocked.  This is important on a FWD car because it helps the car turn in better.  The 4 pinion configuration means that the diff has twice as many spider gears as stock so they are nearly impossible to break.

The Nismo 1 way LSD diff is one of the best differentials for the FWD Nissan transmission.  Too bad it's discontinued.  Cusco makes a good unit as well.  Note the smooth finish on the ring gear.  We WPC treated it for friction reduction.

On the Nismo diff, the end of the pinion cross shaft applies a wedging action on the clutch plate carrier increasing the clamp force on the diff clutch plates. As you can see here, the coasting side of the shaft is flat, so it cannot increase preload on the clutch pack and the other side is pointed so it can wedge into the carrier under drive torque to increase lock.  This defines the diff as a one way which can lock under drive power but remains unlocked when off the throttle.  This helps a FWD car turn in with less understeer.

Although the Nismo diff was one of the best differentials on the market, it was discontinued so you can only occasionally find them used.  Cusco still makes an excellent diff for this transmission and it can be special ordered from Nukabe; Cusco's USA distributor.  A cheap alternative is to assist the viscous LSD with the addition of a Phantom Grip.  The Phantom Grip is an LSD device that uses a pair of spring loaded steel shoes that apply a load to the spider gears, binding them so they act like a limited slip.  A Phantom Grip works very much like an Auburn limited slip favored by the off road truck and muscle car crowd.  Use Phantom Grip’s optional race spring package and shim them for maximum preload with the Nissan viscous diff and you have an inexpensive limited slip differential that is pretty serviceable for high performance use although it is not nearly as good as the more sophisticated Nismo and Cusco diffs.  If there is no limited slip available for your car, a Phantom grip is a good alternative and about your only choice.  In our testing we have not found Phantom Grips to increase understeer in FWD cars.