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Borgwarner Transfer Case Build - Chain Gang

Borgwarner Transfer Case Pulled Apart
Tom Morr | Writer
Posted September 13, 2013

A DIY Rebuild

Like engine timing chains, transfer-case drive chains eventually stretch. The tipoff is often intermittent popping noises or thunks coming from the center of the vehicle. Differences in front and rear driveshaft play when 4WD is engaged and the vehicle is parked are another indicator that the chain is jumping teeth on the sprocket.

Replacing a transfer case chain is entirely doable for anyone who has seal drifts/large sockets and snap-ring pliers. Craig Calkins, owner of CRC Performance Transmission, demonstrated the job. He has 30 years’ experience and does it from memory, but the average enthusiast might want to have a shop manual on hand for torque specs and any model-specific procedures.

Pro Tips

  • Lifetime fluid isn’t. Heat and condensation degrade it. CRC recommends changing it about every 30,000 miles, depending on use and conditions. Chain-drive transfer cases often use ATF. Consult an owner’s or shop manual for recommended fluid.
  • Even electric-shift 4WD systems should be run in low-range (at low speed) monthly. This keeps the actuation motor from seizing.
  • The same model BorgWarner transfer case could be used in multiple vehicles. However, internal parts might not be interchangeable among different automakers.
  • A cracked case is often a death sentence. Less popular BorgWarner applications such as Hyundai and Kia can be expensive in junkyards. New, they might exceed the vehicle’s value. Rockland Standard Gear ( is one comprehensive source for different models and applications.
  • Carefully separate the case. Snapping off an ear can undermine the overall effort.
  • Spray all fasteners and especially plastic parts liberally with penetrating lubricant prior to removal.
  • Inspect clutches for burn marks or wear on the fiber.
  • Mark locations of all brackets and ID tags prior to removal for accurate reassembly.
  • Aluminum case castings can be rough. To prevent leaks, coat the lip liberally with silicone before screwing the case back together.

Step By Step

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  • 1. The ATF in this BorgWarner 4424 full-time transfer case had more than 100,000 miles on it. The “lifetime” fluid was burnt from heat.

  • 2. The loose chain scuffed the case near the corners. Luckily the case wasn’t cracked and the internal magnet wasn’t covered with shavings.

  • 3. Even if the chain is the only worn part, Calkins recommends a thorough cleaning. This requires gutting the internals.

  • 4. The front output seal easily pries out. Its replacement is tapped in using an appropriately sized drift or socket.

  • 5. Calkins smoothed the input shaft’s bearing area with emery cloth. Then he uses a wood block and seal drift to keep the input shaft assembly located on the synchro hub.

  • 6. An assistant is helpful for lowering the case onto the input shaft assembly. Gears need to mesh, and it’s a tight fit.

  • 7. Aluminum cases and chains/sprockets are lighter than cast iron and drive gears. The OE chain (foreground) stretched and was about a link longer than a new replacement.

  • 8. The shift fork assembly goes in next. It’s followed by the lower sprocket.

  • 9. Calkins uses a hose clamp to keep the clutch pack and sprocket together on the shaft (obscured by his hand). Extra hands make installing the shaft assembly and new chain easier.

  • 10. Calkins removed the hose clamp, then bolted the case together. He runs a bead of silicone before installing a new rear output seal.

  • 11. This BW 4424 needed a new shift motor too. Luckily, clutches, gears, and sensors were fine.


CRC Performace Transmissions