A SYE driveshaft is a specific type of driveshaft used in vehicles that have been modified with a Slip Yoke Eliminator (SYE) kit on their transfer case. It is not the SYE kit itself, but the driveshaft required to connect the modified transfer case to the axle.
Understanding the SYE Modification
To understand what a SYE driveshaft is, you first need to know about the Slip Yoke Eliminator.
- A slip yoke eliminator, abbreviated SYE, eliminates the slip yoke from the transfer case and turns it into a fixed yoke that does not slide.
In a standard driveshaft setup on many 4x4 vehicles, one end of the driveshaft connects to a flange on the axle, while the other end is a "slip yoke" that slides directly into the transfer case output shaft. This sliding action accommodates changes in driveshaft length as the suspension moves.
Why is a Different Driveshaft Needed with a SYE?
When a SYE kit is installed:
- The factory slip yoke is removed from the transfer case.
- The transfer case output shaft is often shortened and replaced with a fixed output yoke (a flange).
- Since the driveshaft no longer slides into the transfer case, a different method is needed to handle changes in driveshaft length.
This is where the SYE driveshaft comes in.
Characteristics of a SYE Driveshaft
A driveshaft designed for use with a SYE typically has these features:
- Fixed Yoke Connection: It connects to the new fixed yoke on the transfer case using a U-joint or often a Constant Velocity (CV) joint.
- Slip Section in the Driveshaft: Instead of the slip mechanism being at the transfer case, the slip function is integrated into the driveshaft itself. This is often a splined section within the driveshaft tube that allows it to lengthen and shorten.
- Commonly a Double Cardan (CV) Driveshaft: Many SYE driveshafts utilize a Double Cardan joint (a type of CV joint) at the transfer case end. This design helps reduce driveline vibration, especially on lifted vehicles where the driveshaft angle is increased.
Benefits of a SYE and Corresponding Driveshaft
Installing a SYE and the required driveshaft offers several advantages, particularly for off-road vehicles:
- Reduced Driveline Vibration: The CV joint helps correct driveline angles on lifted vehicles.
- Improved Driveshaft Angle: Allows for higher suspension lifts with less severe U-joint angles.
- Increased Strength: Often uses stronger components.
- Prevents Output Shaft Pull-Out: In extreme suspension droop situations, a standard slip yoke can potentially pull completely out of the transfer case, leading to fluid loss and breakdown. The fixed yoke prevents this.
- Increased Driveshaft Length: Due to the often-shortened transfer case output, the driveshaft itself can be longer, which can improve driveline angles on some setups.
SYE vs. Standard Setup
Here's a simplified comparison:
| Feature | Standard Setup | SYE Setup + SYE Driveshaft |
|---|---|---|
| Transfer Case Output | Slip Yoke | Fixed Yoke (Flange) |
| Driveshaft Slip | At Transfer Case | Within the Driveshaft Body |
| Common Joint Type | Standard U-joint | Often Double Cardan (CV) |
| Stability on Lifted Vehicles | Can cause vibration/angle issues | Improves angles, reduces vibration |
| Output Shaft Security | Risk of pull-out on droop | Output shaft is secure |
In summary, a SYE driveshaft is the necessary component that couples the vehicle's axle to a transfer case that has been modified with a Slip Yoke Eliminator, featuring a different design (often with a CV joint and internal slip mechanism) compared to a standard driveshaft.
