Service Kits

Transfer case service kits bundle the gaskets, seals, bearings, snap rings, and shims needed to rebuild or reseal a transfer case during a teardown - saving you from sourcing a dozen individual parts separately. A full overhaul kit covers internal bearings and clutch packs along with all sealing surfaces, while bearing and seal kits focus on the wear items most likely to fail first. Output shaft seal kits address the single most common source of transfer case fluid leaks. Most transfer cases don't follow a hard mileage replacement schedule, but 4WD systems on trucks and SUVs that see regular off-road use, towing, or fluid neglect typically need attention between 100,000–150,000 miles. When buying, confirm the kit matches your specific transfer case model number - a BorgWarner 4407 and a NP246 use completely different internal components. OEM kits guarantee factory tolerances; quality aftermarket kits from Transtar or National can match that at a lower price point.

Signs you need replacement

• Fluid pooling under the transfer case - Oil dripping from the front or rear output shaft is almost always a failed output shaft seal, one of the most common transfer case leaks on high-mileage trucks.
• Grinding or growling noise in 4WD that isn't present in 2WD - Worn internal bearings produce a consistent rumble or grinding under load, especially noticeable when engaged in 4-High or 4-Low.
• Difficulty engaging or popping out of 4WD - Damaged shift forks, worn clutch packs, or degraded seals can prevent clean engagement or cause the transfer case to drop out of gear under load.
• Metallic particles or a burnt smell in the transfer case fluid - When a fluid drain reveals shiny flakes or smells scorched, internal bearing or clutch wear has already progressed enough to warrant a full inspection and likely a rebuild.
• Vibration that changes with vehicle speed in 4WD - A rough or pulsating feel through the drivetrain, distinct from normal road vibration, can point to worn output shaft bearings or damaged internal components.

Frequently asked questions

• How do I know which service kit fits my transfer case? You'll need your transfer case model number, which is stamped on a tag or cast into the case itself - not just your vehicle's year, make, and model. Common units like the NP231, NP246, BorgWarner 4405, and AAM 226 each have model-specific kits. Cross-reference the part number before ordering, especially on vehicles where multiple transfer cases were used across the same production years.
• Are aftermarket overhaul kits as reliable as OEM for a transfer case rebuild? For most applications, yes - kits from Transtar, Timken, or National use seals and bearings that meet or match OEM specs at a lower cost. The gap matters more on high-load applications like heavy towing or serious off-road use, where a full OEM kit or a known-good remanufactured unit may be worth the premium. Avoid no-name kits with no material specs listed.
• What else should I replace while the transfer case is apart? If you're doing a full overhaul, replace the transfer case fluid and inspect the front and rear driveshaft U-joints - they're easy to access with the case out. On chain-drive units like the NP246, inspect the chain for stretch and replace it if there's visible slack. A rebuild kit typically runs $80–$250 depending on the unit; adding a new chain adds another $40–$80.