Above 2.5" of lift, the NP231's slip-yoke rear output causes driveshaft vibration at highway speed that makes the TJ unpleasant to drive — an SYE kit and CV rear driveshaft eliminates it.
The NP231 transfer case uses a slip-yoke output at the rear — a design where the yoke slides in and out of the output shaft as the driveshaft plunges and extends with suspension travel. At stock ride height, this works fine. Lift the vehicle 2.5"–4" and the rear driveshaft's operating angle steepens beyond what the slip yoke and standard U-joint can absorb without vibration. At highway speed, the resulting vibration feels like a tire imbalance or a failing u-joint — a buzz or thump that comes on around 45–55 mph and worsens as speed increases.
The SYE (Slip Yoke Eliminator) kit replaces the slip yoke output with a fixed-yoke flange. This requires fitting a new rear output shaft with a fixed-yoke companion flange, which then accepts a custom-length CV (constant velocity) rear driveshaft. The CV driveshaft uses a double-cardan joint at the transfer case end that allows steeper operating angles without the velocity variation that causes vibration with a single U-joint. The result is a smooth, vibration-free rear driveshaft at any legal highway speed regardless of lift height.
Tom Wood's SYE kit is the benchmark. Tom Wood's manufactures both the SYE hardware and the companion CV driveshaft, so the entire system is matched and tested. They build custom driveshafts to measured length after the SYE is installed — send them your measurements and they build the shaft to spec. Advance Adapters' SYE ($279) is a reliable, lower-cost alternative that uses the same design principle and works with any quality rear CV shaft.
The Rubicon's NP242 (Select-Trac) transfer case is a different unit with a different output configuration. This SYE kit does not fit the NP242. Rubicon owners with the NP241OR have their own SYE solutions, but the NP241OR is less commonly used outside Rubicon trim and the aftermarket solutions are more limited.
| Part | Vendor | Est. price |
|---|---|---|
| Tom Wood's Custom Driveshafts SYE Kit for NP231 (TW SYE-231) | Tom Wood's Custom Driveshafts | ~$349 |
| Advance Adapters SYE Kit for NP231 (AA-241630) | Advance Adapters | ~$279 |
| Rubicon Express SYE Kit for NP231 (RE3530) | Rubicon Express | ~$299 |
| Tom Wood's Custom CV Rear Driveshaft for TJ (custom-built to spec after SYE install) | Tom Wood's Custom Driveshafts | ~$250 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.