1998 Jeep Grand Cherokee ZJ - NP242 HD SYE Transfer CasePosted in How To: Transmission Drivetrain on October 3, 2014
If you own a 1987-2001 Jeep Cherokee or 1993-2004 Jeep Grand Cherokee, there’s a good chance that it’s equipped with a New Process (later known as New Venture Gear) 242 transfer case. Not sure if your Jeep is equipped with a NP242? Take a look at the shifter bezel. If it lists 2WD, 4WD part-time, 4WD full-time, and 4WD low, it’s a NP242. Still unsure? The round red aluminum tag on the back of the transfer case will also be clearly labeled.
For years, the NP242 has been thought of as a less-desirable T-case in some circles. This was largely due to the limited aftermarket support. Unlike the NP231, which has a wide array of gearing, shifter, and fixed-yoke options, the NP242 had very little in the way of upgrades. That was, until now.
Well known for its ultra-tough, highly durable drivelines, Tom Wood’s Custom Drive Shafts has developed an all-new HD 242 transfer-case slip-yoke eliminator kit. We say “all new” since Wood’s has offered a NP242 slip-yoke eliminator kit for some time. What makes the HD version of the slip-yoke eliminator kit unique is that it actually fits you with a larger and stronger output by upgrading from the standard 27-spline ‘shaft to a 32-spline unit.
The purpose of a slip-yoke eliminator kit is to move the compression and extension cycle of the driveline from the transfer case’s stock output shaft. By transferring the slip/plunge motion to the driveshaft from the back of the T-case, it reduces the chance of damaging the T-case, while opening up greater driveshaft options. Since a slip-yoke eliminator kit is mostly used for lifted vehicles, it allows the user to convert from a standard U-jointed driveshaft to one that is fit with a constant-velocity (CV) joint. A CV-style driveshaft is designed to operate at increased angles, thus eliminating driveline binding and vibration that’s commonly experienced in lifted vehicles. In this case, the HD 242 slip-yoke eliminator kit from Tom Wood’s also places the driveshaft end closer to the output bearing to reduce what’s known as overhung load.
Our V-8–powered 1998 Jeep Grand Cherokee ZJ had received a NP242 swap by the previous owner, but now that it was equipped with a BDS Suspension 6½-inch long arm, it needed a slip-yoke eliminator upgrade. Since we were installing the suspension kit at East Coast Gear Supply in Raleigh, North Carolina, we continued our wrench fest at the company’s headquarters. Since we were able to leave the transfer case connected to the transmission, it greatly reduced the install time. In roughly three hours, we had the kit installed, driveshafts in place, and were ready for the open road.
We started with a late-model version of the NP242J transfer case. What makes the NP242 unique and desirable is the 4WD full-time option. Placing the T-case in 4WD full-time allows a torque bias between the front and rear axles, so the Jeep can safely be operated on the street in 4WD high. This is an especially helpful feature for those navigating more treacherous winter conditions.
The new HD output shaft from Tom Wood’s ups the spline count from 27 to 32. The HD SYE kit includes a new output shaft, speedo gear, tailhousing, and 1350 driveshaft mounting flange.
You’ll need a set of snap-ring pliers and a basic tool set to remove the back of the transfer case. Since the NP242 housing is aluminum, it’s not overly cumbersome.
Be prepared for a slew of bearings to eject after you remove the stock output shaft retainer clip. Clean and grease the bearings before installing the new ‘shaft. A second set of hands will make this process easier.
The NP242J uses a six-pinion planetary gearset. The 2.72:1 low range makes it an extremely versatile case. We’ve found the low-range gearing, combined with V-8 power, to be enough to maintain low-speed control when rockcrawling and high enough to allow for plenty of wheelspin in mud and sand.
After we cleaned the case and inspected the chain closely, we began our reassembly. A light coat of RTV silicone is all that is needed to seal the case halves.
We opted for the 1350, 32-spline output flange. One of the advantages of moving up from the smaller 1310 U-joint is that the 1350 is not only stronger but can operate at higher angles more effectively compared to a 1310 series CV.
Our Tom Wood’s driveline is fit with a 1350 CV at the T-case and a 1350 U-joint at the axle. The 3-inch, 0.120-wall rear ‘shaft is more than capable of transmitting the Jeep’s V-8 power and includes a special service tool so you can keep the constant-velocity joint running smooth for years to come.
Go Pro, Not Hack
One thing we feel it is important to touch on is the difference between the Tom Wood’s HD slip-yoke eliminator and a do-it-yourself hack-and-tap. With a conventional hack-and-tap, you’re not reducing the overhung load of the driveline. When you attach a heavier-than-stock driveshaft, it creates even more stress on the output bearing and shaft end, which can result in catastrophic damage.
The Tom Wood’s kit not only increases the strength of the output shaft but brings the mounting location of the driveline closer to the output bearing. Doing so reduces the stress on the bearing. Sure, a hack-and-tap is cheaper, but it’s nowhere as strong or reliable as the Wood’s HD conversion.