After cryo treatment, we sent our gears to be shotpeened. Shotpeening is the bombardment of millions of tiny steel balls shot at the part at high velocities. It works by compressing and refining the grain structure of the metal on the surface, kind of micro-forging the metal into a harder layer where a crack has a hard time getting started.
Shotpeening changes the structure of the metal about 0.005-0.010-inch deep. The process usually improves the fatigue strength of a steel part by 100 to 300 percent. Shotpeening works well to solve breakage issues on all sorts of steel parts. We shotpeen cranks, rods, axles and many other parts to help prevent breakage. We sent parts to AFCO, an aircraft-certified shotpeener.
Since gears are made from very hard materials, they need special processing to get all the benefits of shotpeening. We blasted our gears with RC 55-65 shot with a 220 size at an Almen intensity of .020; next, we hit the parts hard with larger 330-size RC 55-65 shot at Almen .020. Our theory is, the smaller shot will get into the roots of the gear teeth, but the larger shot will work the surface harder. Any aircraft-certified shotpeener should be able to duplicate our work. If your shotpeener's eyes glaze over when you give him these specs, do yourself a favor and find one who understands this lingo.
So here is the order in which to do these things: polish, cryo treat, then shotpeen. Remember this order. It's important!
Weld your case
The SE-R transmission case has a weak spot where the axle goes into the case on the bellhousing side of the transmission. The case tends to crack from the outside of the case through the axle hole. Once the case cracks, the tranny will leak gear oil from the void. The cracking can be cured by welding in a piece of aluminum to this area to reinforce the case.
Cut a piece of .25-inch thick aluminum to shape and TIG-weld it in place using a skip-weld technique to avoid overheating and warping the case. The welding may inadvertently distort the axle hole to the point where the axle seal may weep around the outside edge. When reinstalling the seal, smear a thin layer of silicone around the outside surface of the seal.
Get good motor mounts
One reason the case cracks is the poor Nissan motor mounts allow the tranny to smack on the cross member when doing hard shifts or when launching the car. The soft, gushy mounts also put a lot of external stress on the tranny, distorting the transmission case under load. We used Jim Wolf Technology (JWT) heavy-duty mounts on Project Phoenix although Energy, Place Racing, and SR20 Development also make heavy-duty mounts. Energy mounts are inserts and are the softest and most streetable. The others allow a bit of vibration to come through. The wheel hop, crashing and banging of the stock mounts put quite a bit of stress on the transmission's internals and the axles as well. Mounts will go a long way in helping prevent breakage.
Use the least amount of clutch to do the jobA solid-hub, hard-hitting three-puck clutch is a sure way to break third gear quickly. Be realistic and pick the least aggressive clutch that can contain the amount of power your engine produces, and by all means avoid a solid hub, puck-type clutch disc.
We used Jim Wolf Technology's Stage III clutch, which has many fiber tuff pucks on both sides of the disc with a sprung hub. Fiber tuff is a semi-metallic friction material that holds large amounts of power well, but smoothly engages-not nearly as grabby as your typical copper ceramic pucks. We also used JWT's Stage II pressure plate with a higher clamping pressure than its standard plate.
For the SE-R, it's better to use a higher clamping load with a smoother, less harshly engaging pressure plate to avoid shocking the transmission.
Run a light flywheel
A lighter flywheel has less rotating inertia and thus doesn't shock the gears as much during shifts. We used a JWT aluminum flywheel, but Unorthodox, JUN, Stillen and Findenza also make good Nissan flywheels.
Use Redline Shockproof Heavy gear oil
This stuff is incredible. It vastly extends the life of the weak SE-R transmission. Shockproof Heavy is blended by Redline to specifically protect transmission gears and help reduce damage to weak gears. Shockproof Heavy forms a cushioning, thick red film on all of the transmission's internal parts. If you wash away the red film with solvent, you'll find a hard-to-remove gold film under the red. What this means, we don't have the slightest clue, but this stuff seems to work.