Suspension & Steering
I have received several questions on aligning the 928 at home recently, so I thought that I would share the info with the list. This is not the only way to align your 928 at home. There have been other suggestions on using lasers - since you can now buy keychain lasers for $10 each, a set of extra wheel centers with lasers mounted on them might be neat.
This is provided for your entertainment only - I will not accept responsibility for damage to you or anything else if you try this and it doesn't work!
Before You Start:
A day or two before you plan to adjust your suspension, find the height adjuster at the bottom of each spring and the eccentric caster/camber adjusters at the outer end of the lower a-arms, and spray them thoroughly with a penetrating lubricant. Check the boots on the upper ball joints. They often are bad, and replacement boots are cheap. The upper ball joints come only in the control arms, and you don't want to know how much they cost! Check the boots on the steering rack.
To measure Ride Height: What and Where.
Front: There is a small flat machined area on the bottom of the cast bracket that holds the rear of the Lower Control Arm, between the ribs. This pad should be 180mm +/- 10mm from the floor for new springs - you are allowed another 10mm for used springs. There should be a max difference of 10mm from left to right.
Rear: There is a small flat machined area on the aft bottom of the large u-shaped bracket that holds the lower transverse control link (the large flat blade). This pad should be 173 +\- 10mm from the floor, with the same 10mm allowance for old springs. There should be a max difference of 10mm from left to right.
How to Measure Ride Height:
First, and most important: You CAN NOT measure, jack the car to change the ride height, lower the car and remeasure! You MUST EITHER measure, jack and change, then drive the car for at least three or four miles before you re-measure; OR measure, change ride height WITHOUT jacking the car, then re-measure. The 928 takes several miles of driving, or using special tool 10-222A to pull the front end down 60-70mm for one minute. Yes, they are serious. Yes, if you don't do it one of these two ways, you will screw up your ride height - and the same thing applies to front end alignment. You will need a tool that you can use to measure the ride height points while manipulating it at arm's length under the car. One possibility would be a pair of yardsticks, bolted together near the centers using a wing nut, making a kind of three-foot scissors. Slip this under the car to the machined pad, put one tip on the floor and one tip on the pad, being sure to keep them plumb, tighten the wing nut, pull it out and measure the height.
How to Change the Ride Height.
Most 928 springs are adjustable. These have a round, notched, threaded nut around the shocks under the lower spring seats. Ed Ruiz found a tool to adjust these nuts - a "Motion Pro Single Shank Nut Spanner, 08-029" at a motorcycle shop for about $16. (Someone bought one of these tools by mail order from a motorcycle dealer in Pittsburgh (tel. 800-860-0686). They refer to it as an "ATV Shock Tool" part no. P529,but it's a Motion Pro 08-029. Cost was about $14 plus shipping.) Turn the front wheels all the way left or right, lube the nut area well with a penetrating spray lubricant, and turn the nut right to raise, left to lower. You can get to the rear (also lubed) with only a little stretching. Adjust the height all the way around and re-measure. When you think that you have it right, drive the car for three or four miles and re-measure, curse and readjust. If your Spring Struts are not adjustable, the only way to change ride height is to change springs or disassemble and add a maximum of two spacers to the lower spring seats, or buy replacement adjustable coil-overs with Koni shocks from 928 Specialists (770-928-4777) or one of the other vendors.
Setting the Camber
Set the camber (the top-to-bottom angle of the wheels). You can check the camber with a 24" level. You want to have 1/32" clearance between the level and the top tire sidewall with the level plumb and touching the lower tire sidewall. The surface that the car is sitting on does impact this - either use a level area, or check the camber, turn the car around and check it again and average the readings. The camber is adjusted by turning the eccentrics on the lower control arms. The camber eccentric is the inner one for aluminum ball joints, the outer one for steel ball joints. If you have aluminum ball joints, change them - they will break. Mark the position of the other eccentric - it adjusts the caster, which you can't measure without special tools, so you want it to stay where it is. You must loosen both eccentrics to move the caster eccentric. After you measure the camber and determine that it needs adjusting, you must either jack the car, re-measure the camber and adjust that camber reading enough to change your original reading to 1/32", then drive the car enough to settle the suspension (several miles!) and recheck the camber; or you must use two metal plates with grease between them under each front tire and adjust without jacking the car. The rear camber should measure about the same as the front, but is adjusted by an eccentric at the inboard end of the rear link (the transverse vertical blade).
Straightening the Wheels
Straighten the front wheels with the steering wheel. If you want to get everything really straight, pull the small plug on the front of the steering rack on the driver's side and turn the steering shaft until you can see the mark on the steering rack thru the hole. This centers your rack. Pull the steering wheel and straighten it if necessary.
Stringing the Car
After you get the front ride height and camber set, adjust the toe-in. Easiest way is to "string" the car, ala NASCAR. Use any four convenient objects to securely hold two strings that run beside the car, at about wheel center height and an inch or two from them, and extending a foot or more beyond the ends of the car. Measure the distance between the strings in front of and behind the car, and make these distances identical. Make the distances between each rear wheel center and its string identical. Make the distance between each front wheel center and its string identical. Check to make sure the distance between the strings is identical in front of and behind the car. Warning! The track is rarely the same front and rear, so don't use just the measurements from the wheel centers to set your string!
Settle the Car (Again)
Before you measure the toe-in, the suspension must be settled by driving the car several miles. You can NOT settle the car by bouncing on the fender - it takes about 6-800 pounds to force the car down, and it must be held there for one minute to settle it. Will your aluminum fenders stand that?
Setting the Toe-In
Measure the distance from the front of each tire to the string and the distance from the back of the tire to the string. Try to be very consistent on where you measure from on the tires. Do the simple math to get the difference between the front and back measurements on the front tires. Adjust the tie rods (loosen the jam nut, turn the tie rod - don't forget to tighten the jam nut when you finish) on the steering rack to get the tires almost straight ahead, with the smallest amount of toe-in (tires closer together at the front) that you can measure.
Aligning the Car
These procedures will get your alignment close enough to drive the car until you can find an alignment shop that will align your 928 WITHOUT JACKING IT UP. If your alignment shop can't or won't do the alignment without jacking the car up, find another shop.
Set your car at the factory ride height. This is where the suspension was designed to work. My car was lowered by the Previous Owner. Raising it to standard height very noticeably improved both the ride and handling. Low may look cool, but it doesn't work well!
I have always done my own alignment so I have some answers and a question. I first adjust the camber. fortunately, my garage has a very flat floor and I use a carpenter's level to get the wheels at the desired camber angle. Turns out that 30 minutes camber is equivalent to 1/8 inch difference in 16.5 inches (16 inch wheel). Do this with the outer(on the 86) cam. I jack the car to relieve load on the lower ball joint, turn the cam, tighten the bolts, lower the car, roll it back and forth, bounce it and finally measure the camber again. It took me maybe ten times starting from scratch.
Second, adjust the castor - and that is where I run into trouble. The real guys have a degree wheel to turn the wheel a fixed amount either way and then measure the difference in camber. I don't have a degree wheel so how do I get the turn angle? Still working on that.
Third, adjust the toe-in. I use a helper (my wife loves to do toe-in) and measure across the tire front and rear and adjust the tie rods equally to get it right. The correct toe-in for mine turned out to be 3/32 inch measured across the 20 inches from the front to the back of the tire. I pick a tread feature that is easy on the front and back. One needs to measure with the tire in several different rotations as the tire is not perfectly accurate. This can be done without jacking the car at all, but I still roll it back and forth a few times to make sure it is in equilibrium.
Finally, drive the car and see if the steering wheel is straight. If not, adjust one tie rod in and the other out the same number of turns - no need to keep measuring toe-in.
Why do I go to all that trouble? I have yet to find a commercial place that will get it right. It doesn't take much of a toe-in error to wear the tires out in nothing flat. With these wide tires alignment is critical. Slight camber errors will cause it to pull one way or the other. If you are going to have an error and aren't going racing, make the error toward the "zero" side of the tolerance (zero camber, zero toe-in).
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