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STEERING ALIGNMENT, the Easy Way - SR-106

At 09:33 AM 8/1/05 -0600, Stan Watkins wrote:
"What is the best method of adjusting toe-in at home?

I am going to suggest using a long straight edge or a string from rear wheel to front wheel to align the front wheels parallel to the rear wheels. But before you do that, you should know (from the Workshop Manual) that the front and rear track width are not the same.
Track WidthDisc WheelsWire WheelsTwin Cam
Front47-1/247-7/847-29/32
Rear48-3/448-3/447-7/8
Difference1-1/40-7/8(-1/32)
Half Each Side0-5/80-7/16(-1/64)
What follows will assume that you have same size tires and same wheel offset all around. If not, then you need to make some additional allowances for front to rear differences, as we are going to be measuring from the outside sidewall of the tires.

You need to find a board, or a stack of shims which I will call "the board" that has thickness equal to the "Half Each Side" dimension from the chart above. The board needs to be long enough to lay across the sidewalls of the tire half way up. With the car sitting on the ground (hopefully about level), turn the steering wheel straight ahead and level, and roll the car fore and aft a bit to settle the suspension. Tape the string to the side of the rear tire or have a friend hold it there. Place the board against the side of the front tire, and hold the string along side of the board for comparison. If the board is not parallel to the string, then adjust length of the tie rod to suit. You will need to loosen the jam nut on the tie rod, and also loosen the band clamp on the outer end of the steering rack boot so you can turn the tie rod for length adjustment. The tie rod has a pair of wrench flats, but you can also use a pipe wrench (if it is too tight to turn by hand). The thread is right handed on both sides of the car, same part number for both ball ends. If the string shows a gap at front of the board, lengthen the tie rod. If the string shows a gap at rear of the board, shorten the tie rod. When the board is parallel to the string, then repeat the exercise on the other side of the car.

When the board will be parallel to the string on both sides while the steering wheel is sitting level, then roll the car fore or aft exactly 1/2 turn of the tire, and repeat the board and string comparison. This is done just in case a wheel might be bent, or a tire may have some slight aberrations in sidewall position (which is quite common). If the string to board gap is no longer equal both sides, then set the tie rod length half way in between, so the gap will be slightly wide in one position, and slightly narrow an equal amount when the tire is rolled 1/2 turn. Then you can take the car for a short drive on a level road to verify that the steering wheel will sit level while driving in a straight line. If the steering wheel is not level you can make additional adjustment. If for instance the steering wheel is tilted slightly to the left when driving straight, then stop and turn it slightly to the right to be level. This steers the front wheels slightly to the right, so to realign them you need to lengthen the left tie rod and shorten the right tie rod exactly the same amount (or vice versa if the steering wheel tilts the other direction).

As a matter of interest, total travel of the steering rack is 7-inches, while total travel of the steering wheel is 2-2/3 turns. 2.667/7=.381 turns per inch (137.16 degrees rotation of the steering wheel). Thread on the tie rod is 5/8-18-UNF, so one turn of the tie rod will be 136.16/18 = 7.62 degrees rotation of the steering wheel. So if you can estimate the misalignment angle of the steering wheel, you can come very close to making the realignment adjustment correct on the first try. If the steering wheel sits about 5-degrees from level when driving straight, then the tie rods need about 2/3 turn adjustment on each side (making one longer and one shorter). When you have the car driving straight with steering wheel level, then you can lock up the jam nuts for the rod ends and tighten the clamps on the rack boots. If in doubt you can do the board and string check again to assure that both front wheels are pointing straight ahead at the same time.

A tiny bit of additional toe in will make the steering slightly more responsive. A little bit of toe out will give slightly higher cornering force (not that you would notice much) at the expensive of a slightly mushy feel to the steering running in a straight line. Up to 1/4 degree either way will likely not cause any noticeable increase of wear on the tires. 1/4 degree on each side moves the tire sidewall in or out about 0.045-inch. Two tires combined move 0.090" total at front and rear, which makes the distance between tires 0.180" difference between sidewalls at front and rear of the front tires. That is relatively a lot of change for toe in. The standard specification is zero toe, or both wheels straight ahead. If you want a little toe in for better steering response, I suggest not to exceed 1/8-inch toe in. More toe in than that will lead to abnormal wear on the outboard 1/3 of the tire tread width.

Once you have the front end aligned and you are driving the car regularly, keep an eye on the tire tread wear pattern. You should give it a quick glance about as often as you change the engine oil and lube the chassis. If the front tires will wear more on the outboard 1/3 of the tread width, you can shorten the tie rods about 1/4 turn each side. If the tires wear more on the inboard 1/3 of the tread, you can lengthen the tie rods about 1/4 turn each side. That 1/4 turn of the track rod will change toe in by about 1/8 degree on each side, or about 3/32" change of toe in (total) at the tire sidewalls.

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