Pinion Angle

Pinion angle is the difference between the driveshaft angle and the pinion angle on the  differential. 

To measure it you must be able to work under the car with the suspension fully loaded and the car level.  You can place jack stands under the rear-end and under the front control arms (as close to the ball joint as possible). A drive on lift will also work for this.

There are two easy ways to measure your pinion, depending on the measuring device you have.

Protractor Measuring Device

Using an angle measuring gauge (adjustable protractor) to measure the difference between the pinion flange and the drive shaft directly.  These gauges are available for under $10 from a hardware store. 

Examine the diagram at the bottom to determine if the pinion angle is nose up or nose down.

1. Place the edge of the gauge vertically against the front of the pinion flange, beside the driveshaft. 
2. Extend the measuring arm forward parallel to the bottom of the driveshaft. 
3. Extend a straight edge under the driveshaft to the measuring arm of the angle gauge.  
4. Hold the straight edge flat against the bottom of the driveshaft and adjust the measuring arm to read the angle. 
5. Depending on the gauge you use, you may have to subtract 90° from your reading to get the correct number. 
6. Your final measurement should be between 0 and 5. 

Angle Finder Measure Device (Gravity type)

Using a gravity angle gauge (Available at hardware stores) to measure the angle between the driveshaft and the ground & the pinion flange and the ground.

Examine the diagram at the bottom to determine if the pinion angle is nose up or nose down.

1. Hold the gauge on the bottom of the driveshaft. Align the gauge front-to-back under the car in line with the driveshaft and read the number from the gauge (Note if angle is up{+} or down{-}). Write down this number.
2. Next, hold the side of the gauge against the front of the pinion flange (beside the driveshaft). Write down this number (Note if angle is up{+} or down{-}).
3. Subtract the first number from the second number.  This is your pinion angle

Edited January 6, 20179 yr by wildweaselmi

Grab a socket from your toolbox.  Get one that will just fit onto the end of the u-joint cap....this u-joint cap will be pointing directly towards the ground.  Place one of the flat edges of the angle finder against the socket.   I use the magnetic side as it helps hold things in place.  Make sure you have everything lined up squarely and all the components are flat against each other.  Note your pinion angle.  The angle shown is right at 25 degrees on my pinion.

Next, you need to find the drive shaft angle.  On my drive shaft, I have a spot, as shown below, where the shaft is perfectly flat AND the magnetic side of the angle finder can fit flush/flat on the tube.  If yours is not like this, you can simply roll your vehicle just enough to rotate the pinion 90 degrees.  This will position one end of the drive shaft's yoke such that it is parallel to the ground.  You can then use the socket and angle finder as you did before when checking the pinion's angle but using the drive shaft yoke this time.

The angle below, for the drive shaft, is also 25 degrees.  And so, my pinion and drive shaft are directly in-line with each other.  There is NO angle at the pinion u-joint, which is what you want when using a CV drive shaft.  All of the angle is taken up in the double cardan joint (the two u-joints at the other end of the drive shaft).

Some folks prefer to have the pinion angle about 1 degree less than the drive shaft angle.  The reasoning here is that when you apply power to the rear axle, it will load the rear axle a bit and the pinion will lift a small amount.  I don't have a problem with this and if you want to set yours up that way, it is just fine.  I have cartridge joints on my lift and so there is no rubber bushings to compress when power is applied....so I really won't see much of a pinion angle change when I apply power to the rear axle.  If this were a vehicle with leaf springs, then you would want to set your pinion several degrees below the drive shaft as the springs will allow some axle wrap which will cause the pinion to lift upwards when power is applied. 

If your angle is not correct, then you must adjust your upper control arms a bit to "dial in" your pinion position.  If the angle on your pinion is several degrees less than the drive shaft, then you need to lengthen your upper arms a bit to bring your pinion and drive shaft closer into alignment.  You may have to check and make these adjustments several times before you have everything set up correctly.  Some folks get lucky and get it right on the first try.

That is about it!  Nothing much more to it than just that....but it is important that you get your pinion angle set up correctly.  Failure to do so can and does result in vibrations, pinion seal leaks, pinion bearing problems, and early u-joint failure.  Take your time and do it right.  You'll appreciate the trouble free service your new SYE and CV drive shaft provide you.

Check out this link at fourwheeler that talks all about this in some more detail

Check out this link at Summit for pinon angle shims

Check out this link describing Drive Shaft Geometry in detail

Edited January 6, 20179 yr by wildweaselmi