The importance of indexing your rear suspension, hope this helps: Indexing (or squaring and aligning) the rear suspension on an asphalt circle track car with a 3-link setup means setting the rear axle completely square to the chassis centerline and zeroing out unwanted rear steer at ride height.
Tools Needed
- Chassis centerline marks or a string setup
- Plumb bobs and a steel tape measure
- Level and angle finder (for the top link and pinion)
- Setup blocks or scales (with the car at static ride height), what this should be is the car at race air pressures "hot," drivers weight in seat and fuel load as the car comes off the track!
Step 1: Prep the Car
Place the car on flat setup blocks or scales at normal race-ready ride height with driver weight (or ballast) in place. Disconnect or neutralize any anti-roll bars or preloads so the suspension hangs or rests naturally without external binding.
Step 2: Establish the Centerline
Locate the true centerline of the chassis using reference points on the front and rear frame rails. Drop a plumb bob from the center of the front crossmember and the rear center of the frame, marking your reference string or chalk line down the middle of the car's underside.
Step 3: Square the Rear Axle Housing
Drop plumb lines from the exact center of both rear axle housing flanges or axle tubes down to the shop floor. Measure diagonally from a fixed, symmetrical point on the front frame (or the centerline) to the left-rear and right-rear axle hub centers. Adjust the two lower trailing arms (the left and right lower links) evenly until the diagonal measurements match and the axle centerline is at a precise 90-degree angle to the chassis centerline.
Step 4: Set the Lower Link Angles (Rear Steer Index)
Check the side view angle of your lower links. At static ride height, you want both lower trailing arms set to your target angle or completely level, depending on your setup sheet, to control roll steer. Ensure the left and right lower link front-to-rear heights match your baseline. Unequal heights create unintended steering effects as the chassis rolls. Center the rear end housing from side to side in the chassis so the tire track width matches your desired side-to-side offset, using a Panhard bar or J-bar adjustment.
Step 5: Adjust the Top Link
Set the top link length and angle. For asphalt, the top link is typically mounted running downhill toward the front at an angle between 12 and 15 degrees. Adjust the rod ends of the top link to set your pinion angle and establish initial bite or drop characteristics under acceleration, making sure it doesn't bind through the suspension travel.