If you lifted your early Bronco 4 inches or more and feel a vibration that gets worse with speed, the rear driveline angle is almost certainly the cause. A slip yoke eliminator paired with a CV-style rear driveshaft is the correct fix. This is not optional on a tall build — running steep angles on a stock single-joint shaft wears U-joints fast and can fail on the trail.
Lift raises the body and axles relative to the transfer case output. The rear driveshaft now operates at a steeper angle, and a conventional single U-joint at each end transmits that angle as a speed fluctuation you feel as vibration. The taller the lift, the worse it gets.
The factory Dana 20 transfer case uses a long output shaft with a sliding slip yoke that the driveshaft rides on. A slip yoke eliminator replaces that long output and slip section with a short, fixed yoke. Two things improve: the driveshaft can be longer (which reduces operating angle for a given lift), and the slip function moves into the driveshaft itself, where a CV joint can handle it.
A side benefit on the trail: the factory long output shaft is exposed and vulnerable. If a rear driveshaft gets torn off on an obstacle, the long slip yoke can let all your transfer case fluid drain out, stranding you. The SYE's short fixed output is far less prone to that failure.
A constant-velocity (CV) joint is a double-joint assembly that splits a large operating angle into two smaller ones, canceling the speed fluctuation that causes vibration. With an SYE setting the rear output to point the driveshaft at the pinion, and a CV joint absorbing the remaining angle, the driveline runs smooth even at significant lift.
The pinion angle on the axle must be set so the CV joint operates correctly — typically the pinion is rotated to point at or near the transfer case output. On a leaf-sprung Bronco this means adjusting shims or perch angle. Measure with a driveline angle gauge before ordering the shaft, because Tom Woods and other builders cut the shaft to your measured length and angle.
This is a capable home-garage job, but two steps demand care. First, the transfer case rear output seal must be replaced when the SYE goes in — reusing an old seal here causes a leak that is annoying to revisit. Second, measure the pinion angle at ride height with the truck on the ground, not on jack stands, or the shaft will be built to the wrong geometry.
If your lift is 2.5 inches or less, you may not need this at all — a quality stock-style shaft with fresh U-joints often runs smooth at mild lift. The SYE-and-CV combination earns its cost at 4 inches and up, or on any SOA build.
Budget $600 for the pair on a moderate build, more if you need a front CV shaft as well on a tall SOA truck. Order the driveshaft only after the lift is installed and the pinion angle is set, so the builder cuts it to the real geometry.
| Part | Vendor | Est. price |
|---|---|---|
| Slip yoke eliminator kit (Dana 20) | Various | ~$280 |
| CV-style rear driveshaft (Tom Woods) | Tom Woods | ~$450 |
| New transfer case rear output seal | Various | ~$15 |
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.