The Jeep XJ’s AW4 automatic transmission is a four-speed unit known for its reliability in off-road conditions. If you own a Jeep XJ, you’ve likely heard about the “Jeep Xj 40 Automatic Trasmission” and its reputation for toughness. This article will guide you through everything you need to know about this gearbox, from its specs to common issues and upgrades.
Let’s start with the basics. The AW4 was built by Aisin-Warner, a Japanese company, and used in the XJ from 1987 to 2001. It’s a hydraulic-controlled, electronic-shifted transmission that pairs well with the 4.0L inline-six engine. Many owners consider it one of the best automatic transmissions ever put in a Jeep.
Jeep Xj 40 Automatic Trasmission Overview
The “Jeep Xj 40 Automatic Trasmission” is actually a misnomer—it’s the AW4, not a “40” model. But the term stuck among enthusiasts. This transmission has four forward gears and one reverse gear. It features a lock-up torque converter for better fuel economy on the highway.
Key specs include a gear ratio of 2.804:1 in first gear, 1.531:1 in second, 1.000:1 in third, and 0.753:1 in fourth. The reverse gear ratio is 2.393:1. The transmission fluid capacity is about 8.5 quarts when dry, and it uses Dexron III or Mercon V fluid.
Common Misconceptions About The Name
Some people call it the “40” because of the 4.0L engine displacement. But the transmission code is AW4, not related to engine size. Don’t confuse it with the later 42RE or 44RE transmissions found in other Jeeps.
Reliability And Durability Of The Aw4
The AW4 is known for its strength. It can handle up to 300 horsepower and 350 lb-ft of torque in stock form. Many XJ owners run 33-inch tires and heavy bumpers without issues. The transmission uses a simple design with fewer electronic components than modern units.
Common failures include the torque converter clutch solenoid and the neutral safety switch. But these are easy to fix. The transmission itself rarely fails unless abused or neglected. Regular fluid changes every 30,000 miles keep it running smoothly.
Why It’s Preferred For Off-Roading
The AW4 has a strong first gear ratio for crawling. It also has a manual shift mode on some models, letting you hold gears. The transmission cooler is built into the radiator, which helps keep temps down during slow off-road driving.
Many off-roaders prefer the AW4 over the AX-15 manual because it’s easier to control on steep trails. The automatic also reduces driver fatigue during long days on the trail.
Common Problems And Solutions
Even though the AW4 is reliable, it has some weak points. Here are the most common issues and how to fix them:
- Torque converter shudder: Usually caused by old fluid. Flush and replace with fresh Dexron III.
- No reverse gear: Often a stuck shift solenoid. Clean or replace the solenoid pack.
- Harsh shifting: Check fluid level first. Low fluid causes hard shifts. Also inspect the throttle position sensor.
- Transmission slipping: Worn clutches or low fluid pressure. A rebuild may be needed.
- Overheating: Install an external transmission cooler for heavy use.
How To Diagnose Shifting Issues
Start by checking the fluid level with the engine running and transmission in park. The fluid should be pink or red, not brown or burnt. Next, test the shift solenoids with a multimeter. They should read 11-15 ohms.
If the transmission won’t shift past third gear, the torque converter clutch solenoid might be stuck. This is a common problem on older XJs. Replacing the solenoid pack is a straightforward job.
Maintenance Tips For Longevity
To keep your Jeep Xj 40 Automatic Trasmission running for 200,000 miles or more, follow these steps:
- Change the fluid and filter every 30,000 miles. Use only Dexron III or Mercon V.
- Check fluid level monthly. Low fluid causes heat and wear.
- Install a transmission temperature gauge if you off-road often. Keep temps below 200°F.
- Avoid towing heavy loads without a cooler. The stock cooler is adequate for daily driving.
- Use the correct fluid. Don’t use synthetic unless specified by the manufacturer.
Fluid Change Procedure
Draining the AW4 is simple. Remove the drain plug on the transmission pan. Let the fluid drain completely. Replace the filter and gasket. Refill with 4-5 quarts of fluid. Start the engine and cycle through all gears. Check the level and add more as needed.
Some owners do a “flush” using a machine. But a simple drain and fill is safer for high-mileage transmissions. Flushing can dislodge debris and cause problems.
Upgrades And Modifications
If you want more performance from your Jeep Xj 40 Automatic Trasmission, consider these upgrades:
- Shift kit: Improves shift firmness and reduces slippage. Available from TransGo or B&M.
- External transmission cooler: Mount in front of the radiator. Reduces temps by 20-30°F.
- Deep transmission pan: Holds more fluid and helps cooling. Adds 2-3 quarts capacity.
- Torque converter upgrade: A higher stall speed converter improves low-end power.
- Manual shift conversion: Add a B&M shifter for full manual control.
Cost Of Common Upgrades
A shift kit costs about $50-100. An external cooler is $40-80. A deep pan runs $100-200. A performance torque converter is $300-500. Labor adds to these costs if you don’t DIY.
Most upgrades are bolt-on and don’t require removing the transmission. The shift kit is the best bang for the buck. It makes the transmission feel more responsive without sacrificing reliability.
Comparison With Other Transmissions
The AW4 is often compared to the TH350 and 700R4 from GM. Here’s how they stack up:
- AW4: Four speeds, electronic shift, reliable, good for off-road. Weakness: No overdrive lock-up issues.
- TH350: Three speeds, tough, simple. Weakness: No overdrive, poor fuel economy.
- 700R4: Four speeds, overdrive, common. Weakness: Prone to failure under heavy load.
For most XJ owners, the AW4 is the best choice. It’s stronger than the 700R4 and has overdrive unlike the TH350. The electronic shift is reliable and easy to diagnose.
Why Not Swap To A Manual
Some people consider swapping to the AX-15 manual. But the AW4 is often better for daily driving and off-roading. Manual swaps require new pedals, clutch master cylinder, and driveshaft modifications. It’s expensive and time-consuming.
Stick with the AW4 unless you really want a manual. The automatic is more convenient in traffic and easier to control on trails.
Rebuilding The Aw4
If your Jeep Xj 40 Automatic Trasmission fails, a rebuild is possible. Here’s what’s involved:
- Remove the transmission from the vehicle. Support the engine and remove the transfer case.
- Disassemble the transmission. Remove the valve body, clutch packs, and planetary gears.
- Inspect all parts. Replace worn clutches, seals, and bearings.
- Reassemble with new gaskets and seals. Use a rebuild kit from a reputable brand.
- Install the transmission and refill with fluid. Test drive to ensure proper operation.
Cost Of A Rebuild
A DIY rebuild kit costs $200-400. Professional rebuilds run $1,500-2,500. It’s often cheaper to buy a used AW4 from a junkyard for $300-500. But a rebuild ensures reliability.
If you’re not experienced, pay a shop to do it. The AW4 has many small parts that must be installed correctly. A bad rebuild can fail quickly.
Finding A Used Aw4
Used AW4 transmissions are easy to find. Check local junkyards, online marketplaces, or Jeep forums. Look for one from a 1996-2001 XJ, as these have the best shift solenoids.
Inspect the transmission before buying. Check for leaks, damaged connectors, and rust. Ask for the mileage and maintenance history. A well-maintained AW4 can last 200,000 miles.
Compatibility With Different Years
The AW4 changed slightly over the years. Early models (1987-1990) have a different shift pattern and no overdrive lock-up. Mid-year models (1991-1995) have improved solenoids. Late models (1996-2001) have a different valve body and use different fluid.
Make sure the replacement matches your XJ’s year. Swapping a late model into an early XJ requires wiring changes. It’s easier to stick with the same year range.
Frequently Asked Questions
What Fluid Does The Jeep XJ AW4 Transmission Use?
Use Dexron III or Mercon V automatic transmission fluid. Do not use Dexron VI or synthetic unless specified. The capacity is about 8.5 quarts dry.
How Do I Know If My AW4 Is Failing?
Signs include slipping, harsh shifting, no reverse, or burning smell. Check fluid level first. If low, top off and test drive. If problems persist, have a mechanic inspect it.
Can I Swap A 4-Speed AW4 Into A 5-Speed XJ?
Yes, but it requires a new transmission crossmember, driveshaft modifications, and wiring changes. It’s a complex swap. Many owners prefer to keep the manual.
Is The AW4 The Same As The A340?
Yes, the AW4 is also known as the Aisin A340. It’s used in many Toyota vehicles like the Supra and Lexus. Parts are interchangeable.
How Much Does It Cost To Replace An AW4 Transmission?
A used transmission costs $300-500. A rebuilt unit costs $1,500-2,500. Labor adds $500-1,000 depending on the shop. DIY installation saves money.
Final Thoughts On The Aw4
The Jeep Xj 40 Automatic Trasmission is a solid choice for any XJ owner. It’s reliable, easy to maintain, and capable off-road. With proper care, it will last for many years.
If you’re buying a used XJ, check the transmission condition first. Look for clean fluid and smooth shifts. Avoid transmissions with a history of overheating or abuse.
For those who already own an XJ, keep up with maintenance. Change the fluid regularly and address issues early. Your AW4 will reward you with dependable service.
Remember, the AW4 is not a “40” transmission, but the name is here to stay. Embrace it and enjoy your Jeep. Whether you’re daily driving or hitting the trails, this transmission has you covered.
One last tip: always warm up the transmission before heavy use. Cold fluid doesn’t lubricate well. Let it idle for a minute before driving. This simple habit extends transmission life.
Now go out and enjoy your Jeep XJ. The AW4 is ready for whatever you throw at it. Happy wheeling, and keep that fluid fresh.