Читать книгу Jeep TJ 1997-2006 - Michael Hanssen - Страница 10

CHAPTER 3

TRANSMISSIONS AND TRANSMISSION SWAPS

The engine has much to do with the “personality” of a Jeep, but the transmission may play a bigger role in the Jeep’s overall capability. A Jeep and its intended use are quite different from most other vehicles that spend their lifetime on the street. A properly matched transmission will only make the Jeep’s use in both on- and off-road conditions better. The transmission is the first part of the three components that are part of the crawl ratio calculation. Crawl ratio is defined and explored in chapter 5.

Factory Transmission Offerings

The Wrangler TJ was equipped with eight different transmissions through its production run. When Jeep changed a transmission model, it was often an improvement over the previous version. Of the five manual transmissions and three automatics, the 42RLE automatic and the NSG370 manual are standouts. These models were installed in Jeeps after 2003. However, the reality is that all of the transmission models are a good fit for the TJ; in fact, the NV3550 is a commonly swapped transmission. Transmission choice among Jeep owners is a matter of personal preference and, like many things, the debate on manual versus automatic continues.

The factory automatic is easily spotted by the shifter sitting in the center console or the presence of a transmission skid plate in front of the main center skid plate. The 4-speed automatic uses the same shifter as the 3-speed. The fourth gear, also known as overdrive, is engaged and disengaged by a switch on the dash.

Manual Transmissions

A manual is the more common type of transmission found in a TJ, with the exception of the TJ Unlimited, which was more commonly fitted with an automatic. Jeep owners often prefer a manual transmission for added control off-road, increased fuel economy, and the fun. Manual transmissions are much simpler in design and create less heat, which, in general, increases life and makes them more reliable. All of the five manual transmissions featured an overdrive gear that kept engine RPM speeds lower, increasing fuel efficiency.

Determining the particular manual shift in a Jeep is difficult by looking only at the shifter. The exception is the NSG370, which has six speeds. The manual transmission is much more common in the TJ series except for the Unlimited, for which the automatic tends to be more popular.

When building and modifying a Jeep, it is helpful to know the first gear and last gear ratio; this is used to calculate overall crawl ratio and highway cruise RPM. Both of these concepts are explored in chapter 4.

Aisin-Warner AX-5

This fully synchronized light-duty 5-speed transmission was used until 2002 in 2.5L-equipped TJ Jeeps. Its light-duty design makes this transmission a poor candidate for a larger, more powerful engine and/or hard off-road abuse. The 21-spline output shaft makes a Jeep equipped with this transmission have a NP231 transfer case equipped with a 21-spline input. Many transmissions and adapters use the 23-spline input.

First gear: 3.93:1

Fifth gear: 0.85:1

Aisin-Warner AX-15

This fully synchronized medium-duty 5-speed transmission was used from 1997 until 1999 in 4.0L-equipped TJs. The AX-15 had wide use in Jeep vehicles, including the YJ Wrangler and XJ Cherokee, and is capable of handling the 4.0L easily along with swapped mild V-8 power. The split cast-aluminum case transmission uses a 23-spline output shaft and an internal hydraulic clutch release bearing. The numbers on the lower part of the case identify the AX-15. This requires a chart listing the many part numbers. An easier way is to check the intermediate plate that is aluminum on the AX-15 and steel in the AX-5.

First gear: 3.93:1

Fifth gear: 0.79:1

NV1500

This fully synchronized light-duty transmission was only found in the 2003 and 2004 2.4L engine–equipped TJ. It is likely the least desired or sought after transmission of the TJ line. This transmission is up to the task of handling the 4-cylinder engine but not much more.

First gear: 3.85:1

Fifth gear: 0.80:1 or 0.83:1

NV3550

This fully synchronized medium-duty 5-speed transmission was used from 2000 until 2004 in 4.0L-equipped TJ Jeeps. This popular transmission is capable of handling the 4.0L power as well as mild swapped V-8 power. It is more than capable of withstanding off-road abuse and its low first gear is a good contributor to overall crawl ratio. There are a couple of things to note. First, the NV3550 is a rather noisy transmission that is even noisier in a Jeep with no carpet. Second, it doesn’t use standard gear oil; it uses the more expensive and more difficult to find Synchromax oil.

First gear: 4.01:1

Fifth gear: 0.79:1

This NV3550 sits ready to go into the Jeep’s frame, freshly mated to the Magnum 5.8L V-8 from a Grand Cherokee. This popular 5-speed transmission, found in Jeep vehicles as well as Dodge trucks, has a respectable low first gear and will handle mild V-8 power. (Photo Courtesy Ben Mann)

NSG370

This fully synchronized medium-duty 6-speed transmission was used in 2005 and 2006 TJ Jeeps with the 4.0L and 2.4L engines. The final two years of the TJ saw the best manual transmission in the run. For the first time, the same transmission was used with both engines, reducing production costs for Jeep and providing an excellent transmission for a V-8 swap for either engine. The NSG370 incorporated many modern improvements that reduced transmission noise and improved shift quality. The 6-speed offered a wider gear range, allowing for increased fuel efficiency and an impressive first-gear ratio. This transmission went on to serve the JK Wrangler as the only manual for its entire 10-year run.

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 volume of air moving through the cooler. To make matters worse, the transmission cooler sits forward of the radiator and will collect mud and dirt that comes through the grille. A clogged cooler will only contribute to increasing the transmission temperature. Be sure to clean the cooler thoroughly after every off-road adventure. Check the fluid regularly and note the smell and color of the fluid. If it smells burnt or is black in color, heat may have been high, and you should consider a flush.

When looking at purchasing a used Jeep, smelling the automatic transmission fluid on the transmission dipstick will indicate if the fluid was overheated because it will smell burnt. Fluid color on the stick should be a lighter to medium brown. Look for the presence of leaks around the pan or torque converter dust cover.

The aluminum transmission cooler sits between the grille and the radiator. Heat is the biggest enemy to an automatic transmission, because the cooler sits in front of the radiator. It often can become a trap for trail debris such as mud and dirt, lessening its cooling ability. Keeping it clean will extend the life of the transmission.

Transmission Swaps