If you lifted your early Bronco 4 inches or more and feel a vibration that worsens 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, and it costs roughly $600-850 for the pair with a custom-built shaft. This is not optional equipment on a tall build: running steep angles on a stock single-joint shaft chews U-joints, and a slip yoke torn off on the trail dumps your transfer case fluid on the ground. Below about 2.5" of lift you likely do not need it — a quality stock-style shaft with fresh joints runs smooth at mild height.
Lift raises the body and the transfer case relative to the axles. The rear driveshaft then operates at a steeper angle, and a conventional U-joint at each end transmits that angle as a twice-per-revolution speed fluctuation you feel through the floor. The taller the lift, the worse it gets.
A single Cardan U-joint running at an angle does not transmit rotation at a constant speed — the output speeds up and slows down twice per revolution. In a stock driveline, the joint at each end runs at the same angle in opposite directions, so the two fluctuations cancel and you feel nothing.
Lift breaks that cancellation in two ways. The operating angles at the two ends are no longer equal, and both are steeper than the joint was designed to run. Practical limits worth remembering:
The other thing to know: a short shaft at a given lift height runs a steeper angle than a long one, because the vertical offset is spread over less length. That is the mechanism the SYE exploits.
The factory Dana 20 uses a long rear output shaft with a sliding slip yoke that the driveshaft rides on. A slip yoke eliminator replaces the long output and slip section with a short, fixed yoke. Two things improve at once:
There is a trail benefit as well. The factory long output shaft is exposed and vulnerable. If a rear driveshaft gets torn off on an obstacle, the long slip yoke lets all the transfer case fluid drain out and strands you. The SYE's short fixed output keeps the case sealed. For a truck that wheels seriously, that alone justifies the cost.
For background on what you are working inside, read the Dana 20 transfer case guide before you start — the case is gear-driven cast iron and forgiving, but the output shaft and bearing stack want to come apart in the right order.
A constant-velocity (double-cardan) joint is a pair of U-joints with a centering ball between them. It splits one large operating angle into two smaller ones and cancels the speed fluctuation internally. With the SYE aiming the transfer case output at the pinion and the CV joint absorbing the remaining angle, the driveline runs smooth even at significant lift.
The pinion angle has to change to match. With a CV shaft, the pinion is rotated to point directly at the CV joint center — not parallel to the transfer case output, which is the setup a conventional two-joint shaft wants. Aim for the pinion within 0-3 degrees of pointing at the CV, with the single U-joint at the pinion end running under 3 degrees. On a leaf-sprung Bronco you achieve this with tapered shims between the spring and the perch, or by cutting and rotating the perches on a rebuilt axle.
Tom Woods, Adams, and JE Reel all build to your numbers, so the measurement is the job.
Order the shaft only after the lift is installed and the pinion angle is set. Ordering off a projected ride height is the most common reason a new shaft still vibrates.
A transfer case drop kit (spacers that lower the case 1") is the $60 alternative and it does reduce driveline angle. The tradeoff is real: you give up an inch of the ground clearance under the transfer case you paid for with the lift, and that is the lowest point on the truck's belly on most builds. It is a reasonable stopgap at 2.5-3" of lift and a poor answer at 4" and up.
If your vibration only shows up under hard acceleration rather than scaling with road speed, the problem is likely axle wrap or worn U-joints instead of geometry — check those against the driveshaft and U-joint upgrade guide before spending on an SYE.
| Item | Typical cost |
|---|---|
| SYE / fixed yoke kit for Dana 20 | $280-400 |
| CV rear driveshaft, custom built | $450-600 |
| Rear output seal and transfer case fluid | $55 |
| Pinion shims | $30 |
| Rear driveline total | $800-1,050 |
| Front CV shaft as well (SOA / tall builds) | +$450-600 |
Budget $600 if you source a used SYE and a shorter shaft, $850 for new parts done properly, and past $1,300 if a spring-over-axle build means the front shaft needs the same treatment.
| Part | Vendor | Est. price |
|---|---|---|
| Slip yoke eliminator / fixed yoke kit for Dana 20 | Advance Adapters | ~$320 |
| CV-style (double-cardan) rear driveshaft, built to measurement | Tom Woods Custom Drive Shafts | ~$500 |
| Transfer case rear output seal | National / Timken | ~$15 |
| Tapered pinion angle shims, pair | Various | ~$30 |
| Transfer case fluid (GL-4 80W-90, 4 qt) | Various | ~$40 |
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.
Trail Manual · About · Privacy · Terms · Database