Z32 300ZX Differentials
The Z32 uses two different rear differentials, both with a viscous limited-slip center (the “V” in their model names). The non-turbo gets the R200V with a shorter 4.083 ratio; the twin turbo gets the bigger R230V with a taller 3.692 ratio to suit its torque.
Specs
| R200V (non-turbo) | R230V (twin turbo) | |
|---|---|---|
| Ring gear pitch diameter | 205 mm (8.07 in) | 230 mm (9.06 in) |
| Ratio | 4.083 (49/12 teeth) | 3.692 (48/13 teeth) |
| Limited slip | Viscous coupling | Viscous coupling |
| Oil capacity | 1.3 L (2-3/4 US pt) | 1.8 L (3-7/8 US pt) |
| Oil | API GL-5, 80W-90 preferred (below 40°C / 104°F) | |
| Filler plug | 39–59 N·m (29–43 ft·lb) | |
| Drain plug | 39–59 N·m (29–43 ft·lb) | 59–98 N·m (43–72 ft·lb) |
The model numbers tell you the size: R200 has a ring gear of about 200 mm and R230 about 230 mm. The R230 is a much larger, heavier unit.
How the Viscous LSD Works
Instead of clutch packs, a viscous LSD has a sealed coupling filled with thick silicone fluid and interleaved plates, built onto the left side gear. When one rear wheel spins faster than the other, the plates shear the fluid, it thickens with heat, and torque is pushed to the wheel with grip. It's smooth and needs no special oil or additive, but it reacts to slip rather than preventing it, and the effect fades as the coupling ages.
- A simple check: with the car in neutral and both rear wheels off the ground, turn one wheel by hand. With a working viscous unit the other wheel will slowly start to turn the same way, and you'll feel resistance. If the other wheel spins freely the opposite way like an open differential, the coupling has lost most of its effect.
- Worn viscous units are common on cars this age. Many owners replace them with a clutch-type or helical LSD, especially on modified twin turbos.
- Clutch-type LSDs need gear oil with a friction modifier; check what your unit's maker specifies.
Ratio Swaps
- The twin turbo's 3.692 is quite tall. A popular change is to fit a shorter ring and pinion to the R230 (around 4.08 is often used) for quicker acceleration, at the cost of higher cruising revs.
- Swapping in a whole differential from the other model isn't a bolt-in: the R200 and R230 have different mounts, half shafts, drive flanges and propeller shafts.
- Any ratio change throws off the speedometer, since the speed signal comes from the transmission.
Maintenance
- Change the oil when the car is new to you and then on a regular schedule. Check the level at the filler plug: the oil should reach the bottom of the hole.
- Fit a new washer on the filler and drain plugs, and always loosen the filler first so you know you can refill it before you drain it.
- Leaks at the side oil seals (where the half shafts go in) and the front pinion seal are common and can be fixed without opening the differential.
- A whine that changes with throttle, or a clunk on and off the gas, points to worn gears or bearings or tired differential mounts.
Sources Used
- Nissan 1994 300ZX service manual, PD section (final drive specifications and exploded views) and 1996 MA section (oil capacities). Read the PD section