In the Shop
As a farm machinery mechanic and writer, Dan brings a hands-on approach that only a pro can muster. Along with his In the Shop blog, Dan writes a column by the same name as well as the Shop Series for Farm Journal magazine. Always providing practical information, he is a master at tackling technical topics and making them easy for all of our readers to understand. He and his wife, Becky, live near Bouton, Iowa.
In The Shop
Feb 12, 2011
You may already know these tidbits about repairing or maintaining driveshafts and u-joints, but I ran into folks with questions this week, so maybe a refresher would be useful.
-When reassembling a two-piece driveshaft, the u-joints on the ends must be "timed." The yoke arms on one end must be in alignment with the yoke arms on the opposite end. If a splined driveshaft is slid together with the yoke arms out of alignment, the driveshaft will have significant vibration. This isn't a problem with a one-piece driveshaft, like the driveshaft on a rear-wheel-drive car, because the yoke arms can't get out of alignment.
-Don't overtighten the small bolts that hold in place the end caps on u-joints. If those bolts are overtightened it puts stress on the needle bearings inside the caps, creates heat, and shortens the life of the u-joint. Proper torque for most vehicle and farm-related u-joint bolts is 30 foot-pounds or less. Pat Fagen, the owner of FastShafts in Des Moines, jokes that he tells customers who don't have a torque wrench to, "put grease on their hand, hold the driveshaft with that greased hand, then torque the bolts till the driveshaft starts to slip."
-Greasable u-joints are one place where it's okay to pump the heck out of the handle on a grease gun. U-joint manufacturers recommend greasing u-joints until fresh grease purges from the rubber seal on each arm of the u-joints "cross" assembly. That way old, contaminated grease is replaced with fresh grease, extending u-joint life.
-And this one is a pet peeve, not necessarily good mechanical advice: Driveshaft/u-joint couplers don't need to have their splines greased. A dry pto shaft is not a bad thing. A dry-lubed pto shaft--with graphite or silicone spray--is a good thing. A pto shaft smeared with axle grease is...a messy nuisance, an example of lubrication overkill guaranteed to make a mess of your hands, your pants, and the inside of your tractor cab. But that's just my opinion.