Transfer Case Shim
Representative Photo, actual item may vary
Representative Photo, actual item may vary
USA Standard Gear ZTNP15128 Transfer Case Rear Output Shim Kit for NP228 NP229
Representative Photo, actual item may vary
What Is a Transfer Case Shim?
Deep inside your vehicle's four-wheel drive system, precision matters down to fractions of a millimeter. A transfer case shim is a thin, carefully sized spacer — essentially a precision washer — installed behind bearings and gears within the transfer case housing. While small in stature, shims play an outsized role in the health and longevity of your drivetrain.
Transfer case shims are installed to achieve two critical outcomes: proper gear mesh and correct bearing preload. Gear mesh refers to how precisely the gear teeth engage one another inside the transfer case. Too much or too little clearance between meshing gears leads to accelerated wear, increased heat, and eventually gear failure. Bearing preload, meanwhile, is the amount of axial force applied to a bearing to eliminate internal play. Get the preload wrong and the bearings will either bind up under load or develop excessive slop — both of which shorten the life of the unit significantly.
Why Transfer Case Shimming Matters
The transfer case is the heart of any 4WD or AWD system. It receives power from the transmission and distributes it to both the front and rear axles, enabling traction on everything from slippery roads to rugged off-road terrain. Because the transfer case is under constant mechanical stress — and even more so when four-wheel drive is engaged — the internal tolerances must be precisely maintained.
Proper shimming directly extends the service life of bearings and gears within the transfer case and contributes to quieter operation. Many enthusiasts and professional builders overlook shimming during a rebuild, but selecting the correct shim thickness is often the difference between a transfer case that lasts another 100,000 miles and one that fails prematurely. Shims must be replaced any time bearings are replaced, since even slightly different bearing dimensions can shift preload and mesh characteristics out of spec.
When Do You Need a Transfer Case Shim?
Transfer case shims are a critical concern during any transfer case rebuild or overhaul. If you're experiencing drivetrain noise, vibration, or rough 4WD engagement, worn or missing shims may be a contributing factor. Shims should also be inspected or replaced whenever:
- Replacing internal transfer case bearings
- Performing a complete transfer case rebuild
- Diagnosing excessive output shaft play
- Addressing gear noise or drivetrain vibration
- Installing new gears or shafts during a performance upgrade
Top Brands for Transfer Case Shims
When it comes to OE-quality internal transfer case components, Crown Automotive is a trusted name among Jeep, Chrysler, and Dodge owners. Since 1963, Crown Automotive has specialized in replacement parts for these platforms, offering one of the largest lineups of transfer case components available — including shims engineered to exacting factory specifications for a direct-fit replacement.