Universal Joints

Universal Joints consist of a Universal Joint Spider (the cross in the middle), bearing caps, and the retaining clips that keep the assembly in place. Most automobiles use the single Cardan-Type.

Replacing U-joints is straightforward and can be done with a special C-clamp tool, hammer and brass drift, or a large and small socket and a vise. We use universal joints on our vehicles to offset the driveshaft angle. They also allow changes in driveshaft angles as the vehicle travels down the road.

The transmission end of the driveshaft remains stationary while the end attached to the differential moves up and down. The angle of the driveshaft from the transmission to the differential while the vehicle remains stationary is called the installation angle.

Each of the universal joints actually has two yokes attached. As the spin of the driving yolk remains constant the trailing yolk actually speeds up and slows down twice for each revolution. This speeding up and slowing down causes a vibration along the driveshaft. Both ends of the drive shaft has universal joints that remain on the same plane so the vibration from the rear U Joint cancels out the vibrations coming from the front. This is called the cancellation effect.

When universal joints are in plane they are said to be in "Phase". Typically an acceptable angle would be somewhere around 3-5 degrees. The more the angle on the driveshaft increases the more vibration. This will also cause premature wear and vibrations as vehicle speed increases. The angle of a driveshaft is checked and adjusted using an inclinometer. It is usually adjusted from the axle end: check with vehicle manufacturer for procedure. It’s rare but if necessary a shim can be added between the transmission mount and the extension housing.