In 1990, development of a successor to the YJ began in Chrysler's "Jeep-Truck Engineering Pre-Program" department under Bob Sheaves and TJ program director, Craig Winn. Mules based on the YJ were built from 1990 to 1993, when formal approval was given for the TJ development program at a 0 million budget. From 1991 to 1992 designers worked at the new Chrysler Technical Center, building on various design proposals. In late 1992, Michael Santoro's TJ proposal was chosen by Tom Gale, Lee Iacocca, and executive management. In May 1993, now with engineering and supplier input, Santoro's final Wrangler production design was frozen at 32 months ahead of initial assembly. Verification prototypes using production bodies were built from early 1994 and tested through late 1995. As YJ production ceased in December 1995, the last pre-production TJ examples were assembled, with start of series of production in January 1996. Unveiled on January 2, 1996, at the 1996 Detroit Auto Show as an early 1997 model year introduction (1996 model year skipped), the TJ was an evolutionary update. It later arrived in Jeep showrooms in April 1996, after 6 years of overall investment and 36 month production development phase.Instead of leaf springs, this updated Wrangler featured a modern coil-spring suspension, front and rear, based on that of the Jeep Grand Cherokee, for better ride and handling, and a return to the classic CJ's round headlamps. The engine is the same 4.0 L AMC 242 Straight-6 used in the Cherokee and Grand Cherokee. A 2.5 L AMC 150 Inline-4 engine was available on entry-level models until 2002. The 2.4 L DOHC 4-cylinder engine previously used on the Chrysler PT Cruiser replaced it for 2003.A right hand drive version of the TJ was available for export markets, and was also offered for sale to U.S. rural route postal carriers. The version offered to U.S. postal carriers was only available with an automatic transmission.

In 1998 (MY1999), the fuel tank became standard at 19 U.S. gallons (72 L; 16 imp gal) capacity. There were some changes between the 2002 and 2003 years. From 1996 to 2002, the side door mirrors were black metal framed mirrors; and from 2003 to 2006 they were plastic molded mirrors. The fit of hard and soft tops is slightly different, and the fabric and colors available changed from 2001 to 2003. In 2002 (MY2003), the 3-speed automatic transmission was replaced with a 4-speed automatic with overdrive. The overdrive can be turned off with a dash switch. The radio bezels went from a rectangle in 2002 to a rounded-edged rectangle for 2003. The sound bar inside was changed to sound pods. The interior seats also changed design, going from a rounder model to one with a distinct separation between back and headrest areas. The standard skid plate was also revised for 2003 to make room for the Rubicon's bigger NV241OR transfer case. The change from the 30/32RH to the 42RLE also gained an additional skid plate. This version of the Wrangler is also notable for being the last production vehicle to use AMC-related parts. The AMC Straight-4 engine was retired after the 2002 model year, and both the AMC Straight-6 engine and the door handles (the latter of which first appeared on AMC vehicles in the 1968 model year) were retired along with this generation in 2006. Like the YJ Wrangler, the TJ Wrangler used both the AMC passenger car door handles as well as the larger door handles off the AMC-built Jeep CJ for higher-end models.

 

Below is a focused, practical guide to the Jeep Wrangler TJ drivetrain for a beginner mechanic. It explains how the system works, what each component is and does, common failure symptoms, safety and tools, and step-by-step procedures for the routine repairs a DIYer will commonly perform. I keep the complex rebuilds at a high level and call out where you need a factory service manual, specialty tools, or professional help.

Quick overview (how the system routes power)
- Engine crank -> transmission (manual or automatic) -> transfer case (front & rear outputs) -> driveshaft(s) -> axle differentials -> axle shafts -> wheels.
- In 4WD, the transfer case splits torque to front and rear axles. In low range it uses additional reduction gears to increase torque at low speed.
- Think of it like a bicycle drivetrain: engine is legs, transmission and transfer case are your gear cluster, driveshafts are chains/rods transferring the push to the rear and front wheels, and the differentials are your rear cassette that lets wheels turn at different speeds.

Major components, what they are and why they matter
- Transmission (manual or automatic)
- Function: selects gear ratio between engine and transfer case. Provides neutral and reverse.
- Key failure modes: gear/grinding, shifting problems, leaks, worn input/output seals.
- Transfer case
- Function: takes transmission output and directs it to front and rear driveshafts; also provides 4WD engagement and low-range gears.
- Parts: input yoke, chain or gear drive, shift forks, output shafts and seals.
- Failures: leaks (seals), noisy chain or gears, hard-to-shift or stuck in gear, worn bearings.
- Driveshaft(s)
- Function: rotates to transmit torque between transfer case and axle differentials. Can be one-piece or two-piece with a center/carrier bearing.
- Parts: shaft tube, yokes, universal joints (U-joints), slip yoke or splined joint.
- Failures: worn U-joints causing clunking or vibration, worn splines, bent or unbalanced shafts.
- Universal joints (U-joints) and CV joints (front axle)
- Function: allow angle changes while transmitting rotation. Front axle shafts often use constant-velocity joints or CV-style designs to handle steering.
- Failures: looseness, rusted caps, lost grease, clunking under load, vibration.
- Analogy: U-joints are like elbow joints—if the joint is loose or stiff you can’t move smoothly.
- Differential (front and rear)
- Function: splits torque left/right and allows wheel speed difference when turning. Contains ring & pinion gears, bearings, carrier, side gears.
- Failures: whining (pinion/preload issues), clunking (worn spider gears or carrier), leaks (axle seals/pinion seal), broken teeth (shock loads).
- Axle shafts / CV axles
- Function: take torque from the differential to the wheel hub.
- Failures: torn CV boots, worn splines, broken shafts.
- Bearings & seals (pinion seal, axle seals, transfer case seals)
- Function: keep things spinning smoothly and keep oil where it belongs.
- Failures: leaks, noise, heat.

Why repairs are needed (the theory)
- Wear: bearings, seals, and joints wear with mileage and contamination (water, dirt). Metal-on-metal surfaces quantify wear.
- Lubrication failure: lost fluid leads to bearing/gear death quickly.
- Misalignment or wrong angles: driveline operating angles cause vibration or premature U-joint failure.
- Impact or abuse (rocking off obstacles, hitting big potholes): can bend shafts, break gears, or damage seals.
- Heat and fatigue: repeated torque cycles cause metal fatigue and eventual failure.

Common symptoms and what they usually indicate
- Clunk when shifting into gear or engaging 4WD: worn U-joints, loose drive flange, worn splines, or transfer case internal play.
- Vibration at speed: unbalanced or bent driveshaft, worn U-joints, bad carrier bearing, or misaligned driveline angles.
- Whine or howl that changes with engine speed: likely gear noise (differential or transfer case), pinion bearing preload or ring & pinion tooth contact pattern.
- Leak under vehicle near center: pinion seal on differential, transfer case output seal, or transmission/transfer case seam.
- Grinding when in 4LO or when engaging: transfer case internals or worn chain.
- Front axle binding in turns (not rolling smoothly): differential or CV issues, wrong gear tooth damage, or axle shaft problems.

Safety and tools (do this first)
- Safety:
- Use quality jack stands on a flat surface. Never rely on a jack alone.
- Block wheels, chock the tires, park on level ground.
- Wear eye protection and gloves.
- Have a fire extinguisher accessible when working with fluids.
- Basic tools you’ll use:
- Metric socket set, wrenches, breaker bar, torque wrench, pliers.
- Pry bars, hammer, punch set.
- Seal drivers or appropriate-sized sockets for installing seals.
- Bearing puller or slide hammer for stubborn bearings/axles.
- U-joint press tool or bench vise for U-joints; hammer and sockets also work.
- Grease gun for zerk fittings.
- Drain pan, rags, brake cleaner.
- Dial indicator and magnetic base + gear marking compound if you attempt ring-and-pinion setup (advanced).
- Important: get the Jeep Wrangler TJ factory service manual (FSM) for torque specs, fluid types and capacities, and model-specific procedures.

Common DIY repairs and step-by-step instructions

1) Replace a U-joint (typical and one of the most common repairs)
Why: A failed U-joint causes clunks on acceleration/deceleration and vibrations.
Tools: U-joint press or sockets & hammer, bench vise or C-clamp, snap ring pliers, grease gun.
Steps:
- Park, chock wheels, support Jeep on stands and remove the driveshaft (mark phasing/position of shaft relative to yoke/flange so you reinstall same orientation to keep balance).
- Clean around the joint and remove the retaining clips (C-clips or straps). If it has straps, remove bolts.
- Press or knock the U-joint caps out from the yoke. Support yoke and avoid bending it.
- Clean yoke bores and inspect for wear. If yoke is damaged replace the yoke/shaft as necessary.
- Install new U-joint: grease new caps (if greaseable), press caps squarely into yoke until snap ring grooves are exposed, insert snap rings.
- Reinstall driveshaft in marked orientation, tighten flange bolts/nuts to spec, and torque to factory value.
- After test drive, re-torque bolts as recommended.

Tips: Don’t reuse U-joint clips. If a cap is tight/corroded, soak with penetrant and use a press. Keep the shaft’s rotational marking so dynamic balance remains.

2) Driveshaft slip yoke splines and splined slip: lube or replace
Why: Dry or worn splines cause clunking and premature wear to transfer case output seal.
Steps:
- Remove driveshaft and slide the yoke off the transfer case output.
- Clean old grease, inspect splines for wear or mushrooming.
- Lightly grease splines with correct grease (use recommended grease to avoid ATF/thick oils mixing).
- If splines are severely worn or the slip-yoke is binding/loose, replace the slip yoke or driveshaft assembly.

3) Replace a driveshaft carrier (center) bearing (if you have a 2-piece driveshaft)
Why: Carrier bearing wear causes vibration and noise.
Steps:
- Support the shaft and remove rear driveshaft and front shaft as required.
- Unbolt the carrier bearing bracket and slide the bearing assembly off the shaft. Use press or puller to remove bearing.
- Install new bearing onto shaft with press or bearing driver; re-install bracket, torque bolts, and re-fit shafts, marking orientation.

4) Replace a transfer case output seal
Why: Seals leak oil and allow contamination; replacing is often straightforward.
Tools: socket set, seal driver or socket, gasket sealant if necessary, pry bar.
Steps:
- Support vehicle; drain transfer case fluid.
- Remove driveshaft from transfer case output yoke (mark orientation).
- Pry / pull old seal out (careful not to gouge bore).
- Press new seal flush into bore (seal lip faces fluid). Use a driver sized to the seal outer diameter.
- Reinstall driveshaft, refill transfer case with the fluid type and amount specified in the FSM.

5) Replace differential pinion seal (rear pinion seal)
Why: Pinion seal leaks are common and allow gear oil loss—dangerous if not fixed.
Tools: large socket to remove pinion nut, impact or breaker bar, puller if needed, seal driver, torque wrench.
Steps (basic):
- Support vehicle, mark driveshaft to flange position, remove driveshaft yoke nuts, remove driveshaft.
- Remove pinion nut (this may require significant torque to break). Support pinion flange to avoid turning the differential.
- Slide pinion flange off and remove old seal.
- Install new seal carefully, ensure it's seated flush.
- Reinstall flange and torque pinion nut to factory spec while setting correct preload. NOTE: pinion preload and shims are critical. If you only change the seal and do not change bearings, you must torque to the exact spec and measure bearing preload (or reuse original crush sleeve or shims in same configuration).
- Fill differential with the specified gear oil.

Warning: Pinion bearing preload and crush sleeve procedures are exacting. If you need to change bearings or install a new pinion, that becomes a full ring-and-pinion setup and requires a shop or advanced tools.

6) Change differential fluid and check axle seals
Why: Regular fluid changes remove metal shavings that indicate internal wear and extend life.
Steps:
- Place drain pan under axle, remove fill plug first then drain plug or remove cover (rear differential limited-slip additives may be needed).
- Inspect fluid for metal shavings (small amount OK; lots = concern).
- Reinstall fill plug and refill with the correct grade (often 75W-90 GL-5; check FSM).
- If fluid level is low because of a leak, identify and replace leaking seal: axle shaft seal (replace by removing axle shaft or hub depending on design), pinion seal as above, or differential cover gasket.

7) Front axle shaft and hub service (Dana 30 common on TJs)
Why: Torn CV boots leak grease; worn CV joints cause clicking and loss of drive.
Steps:
- Remove wheel, hub nut, and brake caliper & rotor as needed.
- If it's a CV-type axle, remove axle nut, detach steering knuckle and pull axle out of hub/differential.
- Inspect boot: if torn, you can replace the boot and joint if the joint is not yet damaged; if joint clicks, replace axle shaft.
- Reassemble in reverse, torque hub nut/wheel studs to spec and verify proper cotter pins if present.

8) Ring & pinion replacement / differential gear setup (advanced)
Why: If ring & pinion teeth are chipped or you have whining that changes with load, you may need a full gear set and proper setup.
Theory: The ring and pinion must have correct backlash, bearing preload, and tooth contact pattern. Backlash is the small clearance between ring and pinion teeth; preload sets bearing tightness. Use gear marking compound to check contact pattern.
Why it’s hard: Requires dial indicator for backlash, torque for bearing preload, and shim stacks or crush sleeve setup; mistakes lead to noisy gears and rapid wear.
Recommendation: If you’re unfamiliar, either follow the FSM very closely and rent specialty tools, or have a shop set gears. If you insist on DIY, gather shims, bearings, new axle seals, a dial indicator, torque wrench, and gear marking compound and follow FSM steps meticulously.

Diagnostics quick guide (how to isolate problems)
- Vibrations at a certain speed: test at different speeds. If vibration occurs only at one speed, suspect driveshaft balance/U-joints. If it varies with engine RPM, look at engine/transmission mounts as well.
- Clunk on acceleration/release: check U-joints, slip yoke, transfer case free play, and differential backlash.
- Noise that changes with vehicle speed but not engine RPM: wheel bearing or axle/differential issues.
- Noise that changes with engine RPM: transmission or engine accessories.
- Leaks near center of vehicle: transfer case or transmission seals; near axles: axle seals or pinion.

Maintenance schedule and tips
- Check and change axle and transfer case fluids every 30–50k miles (more often if you off-road or water-cross).
- Grease u-joints with zerk fittings at recommended intervals.
- Inspect boots, seals, and driveline angles regularly.
- After any driveshaft or differential intervention, do a test drive with progressive load and re-check fasteners and torque.

Fluids and parts notes (general)
- Differential/axle oil usually 75W-90 GL-5 gear oil (confirm in FSM).
- Transfer case: follow FSM—some accept ATF+4, some use gear oil. Use manufacturer recommendation.
- Use new seals and new clips for U-joints. Replace U-joint caps/needles if worn.
- For bearings/seals replacement, use quality OEM or reputable aftermarket parts.

When to seek professional help
- If ring & pinion gears, bearings, or carriers need replacement or backlash/pattern adjustments.
- If internal transfer case damage or complex rebuilds are required.
- If you do not have a torque wrench, dial indicator, or press for bearings.

Final checklist after any repair
- Torque all fasteners to FSM specs.
- Refill fluids to correct levels and types.
- Check for leaks.
- Test drive with progressive loads; listen for noises.
- Re-check torques after a short break-in drive (especially flange bolts).

Summary analogies to keep it simple
- Driveshaft = drive chain on a bike; U-joints = elbows/knees that let the shaft change angle; slip yoke = telescoping joint like a sliding post; transfer case = the gearbox that decides if power goes to front/back and low/high range; differential = a small gearbox at each axle that lets wheels spin at different speeds.
- If any joint or seal fails, the "chain" slips or gets noisy; lost lubrication is like riding a bike with a dry rusty chain—it will wear fast and eventually break.

No-yap closing: For any major torque or gear setup work, get the factory service manual and the right tools. For routine DIY work (U-joints, seals, fluid changes, driveshaft replacement) this guide gives the practical steps and warnings to get it done safely.
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