Measuring the Pinion Angle

When swapping a rear axle, you should always check to see if the pinion angle matches the transmission angle. The pinion will point up and the tail housing of the transmission will point down. Both angles from the horizontal should match.

Pinon up angle should match transmission tail housing down angle

If they don't match, you may end up with strange drivetrain vibrations or resonances at specific speeds. In my case there was a cyclic vibration at 110 kph and 120 kph. I measured the pinion angle using an angle meter and found that the 2000 rear end was pointing up at 7 degrees and the transmission tail housing was pointing down at only 4 degrees.

El cheapo angle meter

Good place to measure the pinion angle is the vertical face

The tail housing universal joints have a good vertical face to measure to also

You can buy shims in different degrees at pretty much all 4x4 off road suppliers - the good news is that they are inexpensive. I purchased a 2.5 degree shim set (closest shim size) - that will put the angle within 0.5 degrees which is good enough for the girls I go out with!

This is an aluminum shim set (two shims) that cost a whopping $9.00!

Here's what 2.5 degree shims looks like sideways

There are steel and aluminum shim sets that you can purchase. Supposedly under heavy loads like 4x4ing, the aluminum ones will crumble. I don't plan on doing any offroading so the aluminum set should be just fine.

Gotchas

One big gotcha is that you have to change the leaf spring guide bolts to longer ones with spacers. The leaf spring guide bolt holds the leaf spring together and has a guide pin that centers the rear axle mounting flange to the springs.

When you add a shim between the spring and rear axle mount, the original guide pin is too short. The solution is to purchase longer guide pins from a offroad shop with spacers. The spacers make up the added thickness of the shims. The same place that supplied the shims will have the longer guide pins and spacers. My cost was about $5.00 for a pair.

After dropping the rear axle by removing the U bolts, I used a pair of C clamps to clamp the springs together before removing the guide pins. Lots of WD-40 and a strong vice grip and the guide pins unbolted.

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Copyright March 2011 Eugene Blanchard