First gear: 4.46:1
Sixth gear: 0.84:1
The NSG370 was the first 6-speed manual used in a Jeep vehicle. It is so well matched to a Jeep that it remained for the entire 10-year run of the Wrangler JK model and beyond. Its 4.46:1 first gear and overdrive gives a wide gear range that works well on- and off-road.
Clutch
All Wrangler TJ Jeeps used a single disc–style clutch with a hydraulic master cylinder and slave cylinder release configuration. The clutch master cylinder is mounted on the firewall next to the brake booster. Depending on the transmission, the slave cylinder configuration varies. The benefits of a hydraulically operated clutch are easier clutch operation for the driver, longer and more reliable operation, and tolerance for both body and/or engine/transmission lifts.
Clutch Upgrades
Replacing the clutch with a stronger, high-performance unit such as those offered by Centerforce can improve clutch performance off-road. The dual friction clutch withstands slow off-road driving when clutch usage can be excessive. A Jeep owner often uses the Jeep’s clutch more in one day off-road than possibly several weeks’ worth of everyday street driving.
All TJs have a provision for a clutch master cylinder even if they were not factory equipped with a manual transmission. When swapping from automatic to manual, adding a master cylinder is only a matter of opening up a few holes and installing. Swapping a whole pedal assembly from a manual-equipped Jeep is the most common practice in this kind of swap.
Centerforce Dual Friction and Centerforce I- and II-series clutches offer greater holding power and are a great upgrade for a problem clutch. The centrifugal weights increase holding power without increasing pedal pressure. A day of off-road driving will give the clutch leg of a Jeep owner a workout; less pedal pressure creates less fatigue. (Photo Courtesy Centerforce)
Some money-to-burn upgrades can include the following. Russell makes a braided stainless-steel hydraulic clutch line for the TJ. The stainless braid prevents deterioration and protects the line from rubbing and thrown objects. The construction of the line is firmer, resulting in a more positive pedal feel. B&M produces performance short-throw shifters for the NV3550 and the AX-15.
Automatic Transmissions
The three automatics offered in the TJ were all excellent transmissions and are extremely capable of serving the Jeep in all situations. As stated earlier, the later model 42RLE is generally considered the best and most desired. Interestingly, the 30RH and 32RH, previously known as the TorqueFlite 904 and 999 respectively, were well-known transmissions used over a 23-year span of various Jeep vehicles.
Learning the two-foot driving technique with an automatic adds an incredible amount of control for the driver and the Jeep. If you can hold the brake while operating the gas when navigating rocks and other obstacles, you can help prevent damage from bouncing. It takes some practice and is even useful with a manual transmission.
As in the manual transmission section, the first- and final-gear ratio will be listed to serve as a guide for calculating crawl ratio and cruise RPM. An automatic creates an increase in torque at slow speeds from the transmission’s torque converter. This allows a higher first-gear ratio without much sacrifice to crawl ratio. A 2.74:1 first gear in an automatic is not a direct comparison to a 4.46:1 in a manual transmission because of the torque multiplication from the converter.
30RH
The 30RH, previously known as the TorqueFlite 904, was used in 2.5L-equipped Jeeps from 1997 until 2002. The lighter-duty automatic is well suited behind the 2.5L but is not considered a good candidate for more powerful V-8 engines. Adapter options are scarce for the 30RH, making other transmission choices more attractive.
First gear: 2.74:1
Third gear: 1.00:1
32RH
The 32RH, previously known as the TorqueFlite 999, was used in 4.0L-equipped Jeeps from 1997 until 2002. This small-sized heavier-duty automatic can handle the power of the 4.0L and many V-8 swaps. Adapter and upgrade options are generally plentiful for the 32RH.
First gear: 2.74:1
Third gear: 1.00:1
42RLE
The 42RLE became the only automatic offered through 2003 and up to 2006 with both 2.4L- and 4.0L-equipped TJs. The first 4-speed automatic offered in this style of Jeep was of a heavier-duty design that was well equipped to handle the power of the 4.0L and V-8 swaps. The transmission is electronically controlled to manage shift points based on sensor input. In addition, the 42RLE is equipped with a converter lock-up mechanism to further increase fuel efficiency. Interestingly, the 42RLE uses a higher overdrive than all other TJ transmissions; it helps with highway-cruise RPM when running lower gears.
First gear: 2.84:1
Fourth gear: 0.69:1
The all-electronic 42RLE was the most advanced automatic in the Wrangler until the end of the TJ series. The overdrive allows for lower axle gears without increasing highway cruise RPM. Its low-hanging, thin-walled automatic transmission fluid pan needs protection from trail obstacles. A factory skid plate offers mild protection at best.
Automatic Upgrades
Upgrades and modifications for the factory automatics are sparse, but a few companies make some upgrades. Skyjacker and Rubicon Express make a deep transmission pan for the 32RH that increases fluid capacity, resulting in cooler operation. The increased fluid prevents a neutral drop condition that is caused by fluid starvation when climbing steep hills; it makes the transmission seem to be in neutral. Because the 32RH is essentially the TF999, shift kits, heavy-duty torque converters, heavy clutches, and other internal upgrades are available from companies such as TCI, B&M, and TransGo.
The 42RLE transmission has limited upgrade options. Some Jeep owners add a larger cooler to help with heat because the 42RLE is known for running hot. TransGo makes a few internal upgrade options for this transmission, including shift kits and improved-flow valve bodies. The transmission is entirely electronically controlled, so traditional internal transmission modifications such as shift kits, are really not possible. If your Jeep is equipped with this transmission, take care of it and enjoy it.
The TJ is equipped with a large transmission cooler from the factory. Nevertheless, adding an extra cooler such as a Derale electric fan–equipped cooler, especially to a Jeep that is off-roaded in hot environments, will aid in keeping the transmission cool.
Transmission Care and Maintenance
In general, both the automatics and manuals will be trouble-free if they are properly maintained. Checking and/or changing fluids according to the Jeep recommended schedule is the first step. It would be beneficial to change the fluid more often on a Jeep that sees a lot of off-road use, especially when water crossings and driving in deep mud are involved. A little water can contaminate the lubricant and cause excess wear and other problems.
Heat is a big enemy to the automatic. Slow off-road driving raises the temperature of the transmission because of the slow speeds and low