Lift an early Bronco a few inches and the stock driveshafts start working at angles they were never built for — the result is a vibration at speed and u-joints that wear out fast. The fix depends on how much lift: 2.5–3" of lift can often be corrected with pinion-angle shims and fresh u-joints, but past about 3.5", and especially with a spring-over conversion, you want a CV (double-cardan) driveshaft built to length. Diagnose the angle before you buy a shaft — a vibration is a geometry problem, not a balance problem, most of the time.
When you lift the truck, the axles drop away from the transfer case and transmission, steepening the angle the driveshaft has to turn through at each u-joint. A single u-joint running at a steep angle speeds up and slows down twice per revolution; that pulsing is the vibration you feel, and it's also what eats the joint. The taller the lift, the worse it gets.
The honest answer: don't reflexively buy driveshafts when you lift. Measure first. A mild lift with correct pinion angle and good u-joints often runs smooth. Tall lifts and spring-overs genuinely need the CV shaft.
An angle finder to measure driveshaft and pinion angles, a u-joint press (a shop press or a screw-type tool), heavy-duty 1310-series Spicer u-joints, and — if the geometry calls for it — a CV/double-cardan driveshaft built to your truck's measured length and angle by a driveshaft shop. For pinion-angle correction you'll want degree shims (leaf-spring trucks) or adjustable suspension links if you've converted to a link setup.
Diagnose first. With the truck at ride height on the ground, measure the angle of the driveshaft and the angle of the pinion (the yoke on the axle) with an angle finder. For a standard two-u-joint shaft, the working angle at each end should be small and roughly equal, and the pinion should point at the transfer case output within a couple of degrees. A spring-over or a tall lift typically leaves the pinion pointing well below the shaft — that's your vibration.
For mild lifts, correct the rear pinion angle with degree shims between the spring and axle (or by adjusting links), aiming the pinion up toward the transfer case output. Replace tired u-joints with fresh 1310s and grease them. This alone cures many 2.5–3" lift vibrations.
For tall lifts and spring-overs, fit a CV (double-cardan) driveshaft. A CV shaft puts a pair of joints at the transfer case end so it tolerates a steep operating angle, and the pinion is then set to point directly at the driveshaft rather than splitting the angle. Have the shaft built to your measured collapsed and extended lengths so it can't bottom out at full droop or pull apart at full stuff.
When you reinstall any shaft, phase it correctly — the slip-yoke splines have a relationship that must line up, marked by an arrow or a missing spline. Reassembling a shaft out of phase introduces its own vibration. Torque the U-bolts or strap bolts to spec.
The most common mistake is treating a lift-angle vibration as a balance problem and sending the shaft out for balancing repeatedly. Balancing won't fix an angle problem; measure the angles first.
Watch driveshaft length at the extremes. On a flexy trail truck, a shaft that's correct at ride height can run out of slip-yoke travel at full droop and pull apart, or bottom the slip and bind at full compression — both are destructive. Measure collapsed and extended length through the full range and have the shaft built for it.
Don't reuse old u-joints to save $50 when you're already under there. A failed u-joint at speed can whip the driveshaft into the floor or the brake lines. Fresh, greaseable joints are cheap insurance.
Pinion shims and a pair of u-joints to cure a mild-lift vibration run $60–120 in parts. A built CV rear driveshaft runs $300–400; a matched front shaft is similar, so a both-ends job lands around $600–700. Tom Wood's and other off-road driveshaft specialists build them to your measurements and know the early Bronco geometry. You probably don't need new driveshafts at all on a 2.5" lift — shims and u-joints fix most of those — so measure before you spend, and put the savings toward gearing if you also went up in tire size.
| Part | Vendor | Est. price |
|---|---|---|
| Rear CV / double-cardan driveshaft (built to length) | Tom Wood's / High Angle | ~$350 |
| Front driveshaft (lengthened or CV) | Tom Wood's | ~$320 |
| Heavy-duty u-joints (1310 series) | Spicer | ~$25 |
| Degree shims or adjustable arm hardware | 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.