Caster Angle Determination
WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1985 GMC Vandura Special, 1985 GMC Vandura, 1985 GMC Rally Camper Special, 1985 GMC Rally, and 1985 GMC Magnavan. However, it is still accessible from the selected car via links, so may be relevant.
- With vehicle on level surface, determine frame angle using bubble protractor or inclinometer. Determine caster angle reading from the alignment equipment.
- To determine an actual (corrected) caster angle with various frame angles and caster angle readings from the alignment equipment, one of the following rules applies:
- A "down in rear" frame angle must be subtracted from a positive caster angle reading. See Fig 1 , Example A.
- An "up in rear" frame angle must be added to positive caster angle reading. See Fig 1 , Example B.
- A "down in rear" frame angle must be added to a negative caster angle reading. See Fig 1 , Example C.
- An "up in rear" frame angle must be subtracted from a negative caster angle reading. See Fig 1 , Example D.
- The dimension "BC" is measured 90° from lower surface of crossmember to inboard rear corner of jounce bumper bracket. See Fig 1 , View A. Using dimension "BC" and appropriate ALIGNMENT SPECIFICATIONS table, find the recommended caster angle.
- If an actual (corrected) caster angle (step 2) does not correspond to a recommended caster angle (step 3) within F1°, make necessary shim changes to bring actual (corrected) caster angle in line with recommended caster angle.