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Driveshaftology:The Ins and Outs of Driveshafts and U-Joints

Posted in How To: Transmission Drivetrain on June 28, 2012
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U-joints are simply awesome! Why? They allow rotational forces to be transmitted around corners. U-joints, Rezeppa-joints, Double Cardan-joints, and CV-joints all allow your driveshafts and axleshafts to spin and your tires to turn. Sounds technical, huh? Not really. It’s actually pretty simple, but if a U-joint or driveshaft is unhappy so is your Jeep. And without addressing the problem you soon will be too! We recently lifted our blue and grey ’01 WJ Laredo with a 6-inch Clayton Off Road long-arm suspension and as a result had to play the game of adjusting pinion angles, driveshaft style, and length in an attempt to make a much taller and more capable off-road vehicle drive down the road without sounding like a DC-3 fighting for altitude.

Follow along as we talk about the ins and outs of pinion angle, driveshaft length, and collapsible driveshafts verses slip-yoke-type transfer cases all with the help, parts, and advice of Tom Wood’s Custom Drive Shafts. We also will show a little more about one of Tom’s products; a NP242 slip yoke eliminator for the early XJ T-case in our ’01 WJ.

What you see here is the U-joint main body, the cross … it’s cross shaped. At the end of each cross is a machined area where the cap lives. This is called the trunion or journal. On the right is a U-joint cap. It’s basically a bearing and race that allow the axleshaft or driveshaft to pivot a few degrees relative to the axis of the U-joint. See all those little needle bearings in the cap? If you accidentally knock off a cap and those bearings fall out you are in trouble unless you can get them all clean and back in the cap. Miss one and your cap is gonna fail! Some U-joints have grease fittings on them. Use ’em to add grease frequently if you’ve got ’em.

This kit is a breeze to install and allows the use of a longer, collapsible, and shiny Tom Wood’s rear driveshaft without having to cut, machine, and tap your NP242’s mainshaft in the driveway. And if you’re confused about driveshaft types, measuring for angles, slopes, U-joints, or any of that high-tech stuff, the company’s website is filled with info.

This is a double cardan, (not cardigan—that’s a sweater) or CV. This type of joint houses two identical U-joints within a coupling that operates the U-joints in equal, but opposite angles. These opposite angles cancel out opposing vibrations for smoother operation. Somewhere along the line “the man” stopped making these things greaseable. We’d like to “grease” the penny pincher responsible (not literally, we are lovers not fighters) because they last much longer when they are greased regularly. Most typically max out at about 30 degrees of angularity. The longer a shaft is the more wheel travel you will have without a CV or U-joint binding.
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Tom Wood's Custom Driveshafts
Ogden, UT 84404

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