CASTOR/CAMBER GAUGE INSTRUCTIONS
For all intents and purposes, this gauge can be considered a finely graduated plumb line - as that is exactly what it is! Before proceeding with any measuring for each factor, make sure the vehicle is on reasonably level ground without any wheel being in/on a significant dip/bump. A perfectly smooth, flat floor is ideal, but not essential providing common sense prevails!!
Camber angle is the angle the wheel/tyre makes with the ground, described as a figure relative to a perpendicular line to the ground.
Set the steering straight ahead, and roll the vehicle back and forth a few times to settle the suspension. To check for level, place the long edge of the board on a flat area of the vehicle known to be level relative to the ground. Note the reading given by FLOOR/CHASSIS LEVEL scale. This figure can then be added or subtracted as appropriate to the reading given by the CAMBER scale. To take a camber reading, simply place the long edge of the board against the tyre utilising the full length of the board, but NOT dead centre of the tyre - the bulge at the bottom where the vehicle weight is resting will give false readings. Angle the board so that the string is just resting against it to help 'damp' the plumb line. Take a reading from the outer CAMBER scale where the plumb line crosses it, then add/subtract level reading as appropriate. This figure is the camber angle.
Castor is the measurement of the amount of camber change over a specific amount of steering motion. Either utilise the wide angled 'V' marked on the board itself by carefully cutting along the lines to form a big 'notch' in the side of the board, or make a template from stiff card/hardboard/plywood. The legs of the 'V' are at 20 degrees from a line formed parallel to the edge of the board. This is used to gauge the amount of steering angle change. Again, settle the vehicle by rolling it back and forth a few times with the steering straight ahead.
Position whichever instrument you've chosen flat on the ground alongside one wheel/tyre with the 'V' straddling it, the outer long straight edge parallel to the wheel/tyre. Use chalk or similar to mark draw the 'V' on the ground. Alternatively if a separate board has been made, this can be left in position on the floor. Be careful not to disturb it though! Something like Blue-tack can be used on solid surfaces. Get an assistant to sit in the vehicle, and turn the steering until the wheel/tyre is parallel one side of the 'V'. Place the long side of the board vertically against the wheel/tyre either at the front or rear edge away from the bulge at the bottom, then take a reading from the inner CASTOR scale where the plumb line crosses it.
Now remove the board, have the wheel/tyre turned until it is parallel with the other side of the 'V' and take a second reading. The difference between the two readings is the castor angle for that wheel/tyre, i.e. add the two figures together ignoring the +/- unless both readings are in the same half of the scale. In this case the lower value must be subtracted from the higher one - and will probably mean you have way too little camber or a bad initial set-up. Repeat on the other wheel.
NOTE: Adjustments to track and camber cam alter each other on certain suspension systems. Re-check both measurements after adjustments to either are made if in doubt.