Jim Smart
August 1, 2001

Angle of the Dangle
Whenever we lengthen or shorten a driveshaft, we have to consider driveshaft angle. Driveshaft angle must be the same as the crankshaft and transmission output shaft for proper function. IED sells a special instrument for this purpose called a magnetic protractor. The magnetic protractor mounts on the differential pinion magnetically, which tells us the pinion angle. It also attaches to the transmission tailshaft housing to determine the angle there too. If pinion angle isn't the same as the transmission tailshaft angle, the rear axle must be shimmed fore or aft to correct pinion angle. We change pinion angle by rotating the rear axle fore or aft around the housing's lateral axis (axle flange to axle flange).

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Driveshaft Troubleshooting Facts
IED knows Jack when it comes to driveline woes. They're here to help you based on solid tried-and-proven experience in more than 20 years of business. Here are some valid pointers.

  • Never overtighten the differential-yoke U-bolts. When you overtighten, the cap may compress the needle bearings, causing friction and premature wear. Proper torque for most U-bolts is 14-17 lb-ft (1 1/16- to 1 1/8-inch caps) and 20 lb-ft for 1 3/16-inch caps. With the naked eye, this is tightening the nut until the lock washer is flat, then giving it one eighth of a turn tighter.
  • Make sure you have the right-length shaft. With the vehicle on the ground, the transmission yoke should show three quarters to one inch of polished surface. If you have to jack up the car to install the shaft, the shaft is too long.
  • Vibration is caused by several things. With the vehicle on a hoist, check the universal joints for side play. No motion, of course, is good. Side play (joint sliding back and forth in the caps) between .0005 and .0015 inch is normal for greaseable universal joints. Excessive side play can, and does, cause vibration.
  • A dent in your driveshaft can cause vibration.
  • Driveshaft runout between .000 and .012 inch is acceptable. Anything beyond .012 inch is cause for replacement.
  • Whenever vibration sources cannot be determined, remove the driveshaft, run the engine, and put the transmission in gear. If the vibration persists, the cause is not the driveshaft.
  • If vibration occurs under hard acceleration only, the pinion angle needs to be adjusted. Move the pinion angle downward one half to one degree, then road-test.
  • If vibration occurs during deceleration, move the pinion angle up one half to one degree and road-test the vehicle.
  • If you're experiencing driveshaft ringing whenever you're shifting gears or putting an automatic in gear, the shaft can be filled with foam or cardboard by IED which will silence the shaft. Do not attempt to do this yourself.
  • If runout is found at either end of the shaft, try rotating the shaft 180 degrees (one-half turn) and road-test the vehicle. It will either get better or grow worse. If it's worse, see IED for help.

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