Before an alignment is done, it is important to make sure all suspension components are in good shape. For example, loose wheel bearings on the front or rear will affect alignment and worn components front and rear will alter the alignment over time. Tire wear will indicate how the suspension and tires are handling the adjustments.
We all know that tires wear. The way the tread wears warns us of potential problems. Tire tread design also affects wear patterns. Individual tread blocks typically found on all season tire tread designs have a tendency to wear resulting in noisy tires as we travel down the road. The sculpted rearward water channeling design of directional tire treads produces smoother long term wear. Tire rotation allows the rotated front tires to flatten out the tread as they ride on the rear. Performance tire and wheel combinations usually end up with larger rear tires for improved traction; rotation is not an option and the tires must be replaced. The chart below will explain typical tire wear.
Tire Tread Wear Patterns
- Cornering: Feathered wear at the outer inch of tread (thin feather-like rubber strips are on the edges). This is unavoidable because it happens during turning.
- Excessive Positive Camber: Smooth wear on the outer tread with poor high speed handling.
- Excessive Negative Camber: Smooth wear on the inner tread with a positive effect on handling.
- Incorrect Positive or Negative Caster: No abnormal tire wear. Negative caster will cause poor high speed handling. Excess positive caster will require extra steering effort.
- Toe-in: Equal cupped wear on the tire’s inner tread (looks like a spoon was used to scoop out the tread)
- Toe-out: Equal cupped wear on the tire’s outer tread (looks like a spoon was used to scoop out the tread)
- Tire Imbalance: Cupped wear across the entire tread usually in a pattern of high and low spots caused by the tire bouncing on the roadway.
Frame and Component Check
A straight, square frame is crucial for mounting the suspension and components on. First, ensure that the front wheels are pointing straight ahead. This can be confirmed by placing a string against the tire at the rearmost point and then against the front tire at the very front. If the wheels are pointed straight ahead, the string should sit flat against the inside and outside of both the front and rear tires. If there is any clearance at the front or rear of the front tire, the steering wheel needs to be turned accordingly until the gap is closed.
Now it is time to take some measurements. I measure from the front to the rear at the spindles to check for a square frame. Then check the distance between the center of the front and rear spindle on both sides. This is tough to do accurately with the tires in place. I measure from the center of each tire horizontally, placing the tape measure at the rear of the front tire and front of the rear tire at the edge of the tread. Of course the tires have to be equal in diameter and pressure for accurate results. If there is more than a 1/4 inch of discrepancy from side-to-side, there is probably a frame or suspension component issue. This means that the thrust line is off and the front tie-rods have been adjusted to compensate for the out-of-square condition. The question is- when does this become a major concern? One or more inches will make it tough to compensate for during the alignment. With a discrepancy of an inch or more it is likely that a frontal impact collision occurred sometime in the Corvette’s life and the frame was pushed back on that corner. Frame work is the next step to get the front and rear back into square.
Bent suspension components can also cause the out-of-square condition. Lower control arms can be subjected to some pretty harsh road conditions, for instance. Usually the evidence is there after you find a problem during the measuring process, such as collapsed rails on the control arm or major dents that will tell the tale. I also check the ride height between the bottom of the lower valance panel to the ground. Factory ride height is typically 8-1/2 inches at all four points, front and rear both sides. Checking the ride height will help to determine if there are any worn out springs. Sagging springs will change the suspension geometry. Jacking up the frame with a floor jack as close to the spring in question is the best policy. If the right rear is lower do not assume that the rear spring is the culprit. It is possible that the right front spring is weak and shifting the weight rearward.
If the frame is square, the next thing to do is inspect the suspension and steering components.
Front and rear wheel bearings should have minimal play without adding drag to the spinning hub/wheel assembly. GM suggests .001 to a maximum .005 movement as the wheel is moved in and out at the top. As standard practice, I check for play and then adjust every set of front wheel bearings before aligning any 1968-1982. Do not pre-load the bearings; tighten the bearings while spinning the wheel until there is slight pressure (16N-m or 12-ft lbs of pressure on the spindle nut). This means minimal pressure with a short wrench, then the spindle is backed off then hand tightened. If the cotter pin hole is not lined up, move it to the loose side to install the cotter pin. I always check the adjustment by moving the wheel a few more times to check play.
In one extreme case, I found a 1982 that had been to numerous shops for alignment and tire balance issues (tire wear and vibration). It turned out the right side front spindle was worn at the inner bearing causing .050 play at the wheel. This condition was exacerbated at the outside of the wheel’s diameter causing vibration and inaccurate alignment. New bearings do not absolutely guarantee tight wheel bearings. If you still have excessive play check the spindle’s wheel bearing surfaces for wear.
Inspect the front suspension’s upper and lower control arm bushings, especially the lower rear bushing that is below the power steering pump. Years of fluid dripping on the bushing turn it into a gooey mess, softening it until it falls apart. If you see chunks of rubber coming out of the bushing’s metal sleeves there is no use in aligning the car. Bushings that are cracked but intact should hold an alignment at least for a while.
Next, the steering linkage should be inspected. A loose idler arm is the most common wear item that I see. Tie-rod ends do wear, but should safely go 100,000 miles (if properly lubricated) before they require replacement. The preferred way to check the idler arm and tie-rod ends is to have someone turn the steering wheel back and forth in the free-play range; this usually has the steering wheel moving a few inches either way with the engine not running. As the steering wheel is moved watch the idler arm. If it is moving up and down as it moves side to side, it requires replacement. If the tie-rod ends are moving with any play they should be replaced. They too will move up and down before moving a steering component when worn. The additional load on the steering box when the engine is not running will also bring to light worn steering couplers. Worn steering couplers (often called the “rag joint”) are often missed during steering inspection and many good steering components are replaced as a result.
Rear Wheel Bearings/Suspension Bushings
The 1963-1982 Corvette rear wheel bearings should also be held as close to the .001 play as possible. The bearings are not adjustable except during wheel bearing replacement/servicing. Shims are used to set end-play during bearing service and require specific tools and equipment. If excessive play is found, expect to disassemble and replace the rear wheel bearings. While this service is performed have the trailing arm bushings checked for rubber deterioration. In the majority of cases when the rear bearings require service the trailing arm bushings are usually close to the end of their life expectancy. Loose trailing arm bushings will cause a scary rear toe steer issue that can get you into trouble as the throttle is applied and released. As the throttle is briskly applied the rear of your Corvette will move to one side steering you into oncoming traffic or off the road. When the throttle is released the opposite reaction occurs. Do not expect an alignment to get rid of this phenomenon; if anything it can become worse as the worn bushing is subjected to the rigors of alignment. Many alignment shops are not aware of the rear toe steer issue because it is unique to just a handful of vehicles.
Worn camber control bushings (rear strut rod) are easy to spot as the rubber is forced out of the metal sleeves. I see many that require replacement, especially the early 1963-1974 smaller diameter bushings. As the bushings wear, negative camber results (tire tilted inward at top). This will not cause a poor handling issue but you can expect tire wear on the inner portion of the tread. If anything, better handling would be experienced during high speed cornering on any slightly banked road surface. Keep this fact in mind as I discuss the alignment specifications we are using.
A point to remember is that the 1963-1982 Corvette rear suspension relies on the differential as a centering point for the rear wheels. The rear axle shafts’ yokes set against the differential carrier pinion gear’s shaft. In most cases the shaft wear is minimal even after 100,000 miles while the axle shaft yokes that ride on the shaft can become quite worn. This wear exacerbates the negative camber from worn strut bushings that usually requires differential servicing to allow correct camber adjustment. This wear can be seen usually as the rear of the Corvette is lifted; the axle shaft yokes will be pulled out of the differential a ¼” or more from where they were residing before lifting. Sometimes this axle shaft yoke wear is mistaken as wheel bearing play as the wheel is grasped top and bottom and checked for movement. If you have someone push on the wheel at the top, worn yokes will show movement of the axle shaft inward positively identifying worn yokes. In extreme cases the yoke U-joint straps will be cutting into the differential case; this also indicates missing snap rings that retain the yokes in the differential carrier. The end of the yoke wears away allowing the snap ring to pop off the yoke and it settles at the bottom of the differential case. This will require differential removal, yoke replacement, and a check of all the internals.
If all of the components pass the inspection, air pressure should be adjusted to the tire manufacturer’s specifications, not what the sticker in the door jamb suggests. Tire technology has changed dramatically since the early ‘80s and the recommended tire pressures have too. Tire pressure affects ride quality immensely; lower pressures alleviate some of the 1963-1980 Corvettes’ inherent harsh ride quality. The downside is the lower pressures also negatively affect handling, especially during cornering. A compromise is to drop the pressure during in-town trips where speeds do not exceed 55mph and when it is time for some performance driving or extended high speed highway driving raise the pressure to the tire manufacturer’s specifications. A safe rule of thumb is, do not lower the air pressure more than 10 pounds below the recommended pressure for inner city driving or raise it at all above the recommended pressures.
I recommend replacing the 1963-1980 Corvettes’ rear spring composed of steel leaves with a fiberglass mono-leaf spring for the best possible ride and handling. Using a fiberglass mono-leaf spring will allow you to keep the tire pressures at the tire manufacturers’ recommended pressures without the associated harsh ride. This statement has to be kept in perspective though. If you are using 17 or 18 inch wheels with narrow sidewalls you can expect a harsher ride than with the original 15 inch tires with more flexible sidewalls. A steel spring equipped 1968-1980 Corvette with 18 inch tires inflated to the recommended 44psi would make for an extremely rough ride (kidney belt, anyone?).
Before we delve into alignment specifications here are a few of facts to consider. Radial tires came into the market about midway through the 1968-1982 Corvettes’ generation. The 1963-1982’s steering and suspension consisted of the same pieces that started the second generation Corvette “all new for 1963 with power steering for the first time.” It wasn’t until 1984 that the Corvette chassis was actually built around the radial tire. Those alignment terms I briefly touched on earlier can be sometimes tough to explain and understand. We hear about toe, camber, and maybe caster today when discussing the alignment at most shops. Most late model cars are net build assemblies with very few adjustments available- most only allow toe adjustments. If camber is out a trip to the body shop is required for a late model vehicle. Sharks or third generation 1968-1982 Corvettes allow caster, camber, front toe, and rear toe adjustments. When the alignment technician frowns you will know why. Another tidbit of info: 1968-1970 Corvettes used rear toe adjustment shims that required trailing arm pivot bolt removal for shim changes. That frown only gets uglier when the pivot bolt has to be removed especially if it is frozen in place from corrosion.
Let’s demystify caster first. Negative caster refers to the spindle centerline being forward of the lower ball joint while positive has the centerline behind the lower ball joint. Zero caster is bad for handling as the lighter steering weight placed on the spindle allows any road variation to move the wheels and the steering is also very sensitive. Unfortunately, non-power steering equipped Corvettes will be very difficult to steer in parking lot situations when the caster is in the 1-1/2 to 2 degrees positive range. Experienced alignment techs will use 1 or less degrees of positive caster to avoid customer complaints of difficult steering. Power steering equipped Corvettes benefit from easier, quicker steering while allowing more positive caster for better handling. This is truly one of those situations where you are better off using some horsepower to gain the power steering advantage and handling.
Positive caster loads the spindle making the wheels want to naturally be in a straight ahead stance. This straight ahead stance makes for excellent high speed handling, but like everything in life there is a tradeoff. Expect increased steering load as more positive caster is adjusted into the suspension. That is one of a few reasons why the 1968-1982 Corvette has less positive caster than the 1984 and up Corvette. The original equipment control arms will not allow more than 3-3/4 degrees of positive caster. Corvette Central has a set of tubular a-arms by Van Steel that will allow up 6 degrees of positive caster for much better high speed handling. Part number 572218 and multiple other options are available for the occasional to frequent auto cross road racer.
Camber concerns the tilt of the wheel in or out. The top of the wheel out further than the bottom would indicate positive camber and the top of the wheel in would indicate negative camber. Unlike caster, negative camber is a good thing because most roadways have a slight bank to them. This keeps the tire contact patch at its optimum. Positive camber is never a good feeling and results in very nervous steering input from any road variation.
Toe in or out affects handling and speed. Excess toe-in or out will cause tire drag and hurts performance. Ideally you want the toe to be zero while the steering is loaded going down the road. Many alignment specifications ask for a quarter toe in or out to compensate for steering flex.
1963-1982 Corvette Performance Alignment Specifications
Caster: positive 3-1/4 degrees (plus or minus ¼ degree) (there should be no more than a ½ degree variation side to side). To offset for crowned roads set the left caster to 2-3/4 degrees positive and the right 3-1/4 degrees positive. Not all 63-82 Corvettes will allow the 3-1/4 while some may allow another ¼ degree, the idea is to max out the positive caster. This will affect steering feel requiring more effort during turning while allowing the steering wheel to return to center quicker.
Camber: ½ to ¾ degree negative front and rear. Track only cars: 1-1/4 degree negative front and rear
Toe-in: ¼ inch positive total both wheels
Caster setting: positive 2-1/4 degrees (plus or minus ¼ degree) decrease left side caster ½ degree for crowned roads.
Camber setting: 0 to 1-1/2 degrees positive
Toe-in: 1/8 inch positive to ¼ inch positive
Story and photos courtesy Chris Petris