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Driveshaft Tech You Need to Know - 4-Wheel & Off-Road Magazine

OK, we admit it-no one considers driveshafts when building the ultimate off-road machine. If you have two, you're in business, right? Wrong. Just like every other component of your 4x4, a little thought invested in your driveshafts can pay off with fewer future problems and better performance.

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Denny Bringhurst of Denny's Drive Shaft Service reminded us of this when we called to order new shafts for an early Bronco and he responded with a barrage of questions: What's the truck used for? How much is it lifted? Are the axles rotated or are the pinion angles stock? Has the transfer case been lowered? How much travel do the front and rear suspension have? How's the exhaust clearance on the front shaft? "C'mon, Denny, we just need a couple of driveshafts." Yet he insisted on knowing the Bronco's specs so that he could build the best shafts possible for it, and here's what we learned through the process.

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U-joint or CV joint? This decision is based more on the angles under your 4x4 than personal preference. If the pinion angle and the angle at the transfer case aren't exactly the same, you're likely to get driveshaft vibration using U-joints at both ends of the shaft. A CV joint will overcome this, but a CV joint can't work with as great an angle as a U-joint of the same size. Remember that the U-joint angle must be checked with the axle dangling at full suspension droop as well as when the 4x4 is sitting on level ground. Bringhurst's final note on U-joints is that he prefers to use Spicer nongreasable types. These have proven durability and are sealed to keep mud and water out.

CV joint tips: The Spicer CJ joint provided with this Denny's driveshaft came with bolts but not lock washers. Bringhurst says that this is the way they come on OE trucks and that Loctite should be applied to all four bolts. The CV joint has an inverted grease fitting and should be lubed every 2,000 miles. We required a new output yoke at the rear of the transfer case to accept the CV joint. Ford used at least two different output yokes on the rear of the Model 20, so you'll need to measure yours if you need to replace it. Denny's stocks all popular output and pinion yokes.

Shaft diameter and slip joints: Since this Bronco will be used hard and has a Cold Duck dual-transfer case setup (which multiplies the torque of the V-8 almost five times before it's transmitted through the driveshafts), we opted for Denny's Heavy-Duty driveshafts. However, the specs are different for the front and rear. Bringhurst prefers to build 2 1/2-inch-diameter driveshafts because he says this yields an extremely strong tube, allowing for an optional longer slip joint. Our front shaft could be only 2 inches in diameter because of space restrictions imposed by the exhaust system. You can see that the maximum extension of the slip yoke is considerably less on the front shaft. The slip joints must be lubed with an extreme pressure grease, not generic chassis grease. Bringhurst says most auto parts stores carry the correct grease, but he sells it if you can't find any locally.

Driveshaft Tech You Need to Know - 4-Wheel & Off-Road Magazine

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