Talk to Joe Viereckl for a while, and you begin to value the skill, experience and investment behind repairing driveshafts and making good replacements. Viereckl is president of Midwest Driveshaft, St. Charles, Ill., and his shop fabricates an average of 350 driveshafts monthly for customers as varied as ready-mixed suppliers and racecar owners. And to serve customers expediently, Midwest inventories a wide range of tubing and end-fittings, which are assembled into new driveshafts, then straightened and balanced, on two $80,000 fabricating machines.
Although a few operations that maintain trucks and equipment may handle all their driveshaft work in-house, most rely on independent shops, like Midwest, or on equipment dealers. One notable exception, however, is the installation of new universal-joint (U-joint) bearing kits. Many truck and equipment owners consider installing the kits, which consist of the journal cross and bearing-cup assemblies, a routine-maintenance procedure and handle it in their own shops. What's not widely known about this seemingly simple repair, though, according to Dana's Spicer Driveshaft Group, is that the potential off-center condition of the new pieces may upset the driveshaft's balance. The best advice, says Spicer, is to have the shaft balanced after the repair.
Another caution when installing new bearing kits, says Viereckl, is to check the wear on yoke cross-holes. Worn, out-of-round cross-holes can't properly retain bearing-cup assemblies, and subsequent shaft failure could result. When a driveshaft shows signs of overall wear, he says, you might be money ahead replacing it, versus attempting repair. A shaft that comes unbuckled under a truck or wheel loader is a terrible safety hazard and has the potential to take lots of other expensive hardware with it.
Whether or not you perform any of your own driveshaft work, you can lengthen shaft life with proper lubrication, the lack of which, says Spicer, is one of the most common causes of U-joint and slip-tube/slip-yoke problems. Some premium U-joint and slip-member assemblies are sealed and need no lubrication, of course, but most driveshafts still need the right grease at the right time to keep working reliably.
Always follow the recommendation of the vehicle maker or driveshaft supplier for the lubrication interval, which may vary with the application. Also follow the recommendation for the specific grease type required, because some assemblies do, indeed, require special lubricants. Most vehicular driveshafts, however, according to Spicer, will be served well by grease with an E.P. (extreme pressure) rating, a Timkin Test Load rating of 50 pounds (minimum), an E.P./Grade-2 specification from the National Lubricating Grease Institute and an operating temperature range of 325F to minus 10 F.
When greasing U-joints, purge all four bearing assemblies until fresh grease appears outside the seals (at the bottom of the bearing cup). This procedure flushes contaminants and reduces the risk of grease incompatibility. (See our Quick Tip for more about grease incompatibility). If any of the bearings fail to purge, says Spicer, try moving the driveshaft side-to-side while applying grease-gun pressure. Or, if two grease zerks are present, try the other. If these procedures don't work, you may have to release tension on the seals that are not allowing grease to pass. If you do this, follow the procedure detailed by the vehicle or U-joint manufacturer.
Typically, you can use the same grease in the slip-tube/slip-yoke assembly as in the U-joints, applying grease until it appears at the seal. In cold temperatures, Spicer advises driving the vehicle immediately after lubrication to distribute grease through the slip joint, thereby avoiding possibly popping the welch plugs in the ends of the assembly.
Regularly inspecting driveshafts can help you avoid costly breakdowns. When you inspect the shaft, however, do so before it is lubricated. Fresh grease, says Spicer, can mask looseness in a component that may need replacement. An overall initial inspection should include a check of the driveshaft tube for signs of twisting, denting, scratching and cracking. If this type of damage is evident and looks significant, have the shaft evaluated by a professional. (Aluminum driveshafts are especially sensitive to damage. Consult the manufacturer for conditions that render the shaft unusable.) Also, check the shaft for missing balance weights and for any stuck-on concrete or road tar stuck that could upset balance.
To check the soundness of yokes attached to drivetrain components, grip the yoke (it's part of the U-joint assembly, of course) with both hands and try to move it both vertically and horizontally. Note any looseness relative to the driveshaft. If it's loose, check the retaining nut and follow the component manufacturer's recommendation for repair. If the yoke is tight, again grip it with both hands and try rotating it back and forth to check for radial play. Looseness may indicate either the need for a new yoke or that the component's input/output shaft is faulty.
To check the overall soundness of the U-joint's bearings, grip the shaft just behind the U-joint and try to move the shaft vertically and horizontally. Just a small amount of looseness could indicate the need for a bearing kit. Also, check the general condition of bearing-cup mounting hardware, as well as the yokes for cracking and distortion. Slip-tube/slip-yoke joints can be checked by moving the assembly side-to-side and checking for looseness. Again, any looseness could indicate wear and the need for a new shaft.
If you want to learn more about problems that befall driveshafts, check out Spicer's online "Failure Analysis Guide." You'll find driveshaft failures graphically depicted, along with an analysis of causes. The navigation route is www.spicerdriveshaft.com, click on "Literature Online," select "Commercial Vehicle" from the drop-down menu, then select "Failure Analysis Guide—Driveshaft Components."
Construction Equipment acknowledges Dana's Spicer Driveshaft Group for the information and illustrations used in this report.
