Porsche 944 Four Wheel STRING Alignment Guide
This particular task is not likely to be of interest to most but for myself the task of doing a wheel alignment in my own garage was preferable to arranging a trailer and time to get the car to a wheel alignment shop to have the work done. I have previously done a string alignment to the front wheels and then had it checked at a quality alignment shop and verified that the string alignment results were spot on so I am confident that a string alignment can be very effective. The incentive for doing this again and as a 4 wheel alignment is that I recently replaced my front struts and changed from torsion bars to rear coil overs so my previous alignment was disturbed and required a new alignment.
8 100x200x400 wooden blocks
4 250x250x4mm MDF sheets
String line and two heavy posts
2 x plumb bobs and posts
A pair of “string line calibration bars”
Toe adjustment tool
24mm wrench for toe tool
27mm wrench for camber eccentric
Plus the usual assortment of common tools.
Its not too difficult to align the rear if the car is raised and placed on blocks of timber. I used a pair of blocks measuring 200x100x400 under each wheel. So the wheel was 200mm off the ground and there was plenty of space to work under the car.
The rear suspension plates need to be loosened slightly to enable toe to be adjusted, which is most easily done by removing the road wheel to access the bolts. The wheel can then be put back on and the car can then be put on the blocks.
Then it’s a case of getting under the car and setting the camber and then the toe to desired specs, this involves slight rotations of the eccentrics and then measuring the wheel rim to string line spacings. Once the settings are as desired it is possible to lock the alignment in place by tightening two of the bolts that secure the suspension plates together. The third bolt can be tightened later with the wheel removed.
A pair of the listed MDF sheets under the front tyres allows the front toe to be adjusted easily by allowing the front wheels to turn in or out easily as there is little friction between the MDF sheets.
STRING LINE CALIBRATION BARS
|The strings need to be run parallel to
the centerline of the car. I find the best way to do that is to mount some
bars on the car as can be seen in the adjoining pics. The bars stick out
6-12" either side of the car and carry pen marks on a bit of tape near their
outer ends, the pen marks are equidistant from the centerline of the car.
When setting up the strings, the plumb bobs will be positioned so that they
are above the pen marks and the strings will be positioned so that they are
barely touching the plumb bob lines. Thus the strings will be parallel to
the centerline of the car.
The bars are made from PVC Tube and the brackets are simple 90 brackets from a hardware store and secured to the bar using some hose clamps. I also attached some tiny wooden blocks to the brackets for the front bar. The brackets for the front bar are spaced so that they reach the outer edge of the caster blocks and the little wooden block actually catch the edge of the caster block so that the bar can hang there without any type of clamp (see pic directly below).
The rear bar brackets should be spaced so that they come to the outer edge of the torsion bar cover mounting bolts (Bolt E in the grey scale diagram below). I use a quick clamp to hold the bracket in place on each side although you could create a way to hang it of those bolts.
So with the bars mounted to the suspension points like this the centerline of the car is the midpoint between the brackets on the front and rear bars. Before making the measurements just make sure that the brackets are square and a snug fit without having to bend or warp to mount to the designated points. Then find and mark the midpoint between the brackets. From the midpoint on each bar come out a distance of about 760mm and mark the bar, this will be the reference point for the plumb bobs.
These are the dimensions of the bars as I made them:
Length 2000mm, 32mm diameter
Front brackets 65x65mm, Spacing between bracket (metal) 755mm & 730mm spacing between the small wooden blocks).
Rear brackets 100x100mm and 1137mm spacing between brackets.
Remove rear wheel and loosen Bolts A & B & C, this will allow movement of the plates when the toe eccentric is rotated.
Remove bolt from drop link to rear sway bar, this will later allow free access to the camber adjustment bolt.
Loosen nut that attaches sway bar drop link upper bushing, (Nut on oppsosite end to nut C) this will prevent the drop link from being rotated to an odd position when the camber is adjusted.
Put the wheels back on, raise the car and place on blocks, WARNING: ensure the car is in gear/hand brake applied.
Set up string lines
Check the rear camber using a camber gauge.
Adjust the camber eccentric using a 27mm wrench until the camber is set, The camber eccentric is on the opposite side of the plate to bolt C, this is a bit of trial and error which involves rotating the eccentric a bit then getting out from under the car and checking the camber, then getting back under the car and rotating the eccentric some more etc. Once set tighten the 19mm nut (nut C) slightly to prevent further rotation of the camber eccentric.
Check the string lines are true to the plumb bobs and that the plumb bobs are aligned to the calibration marks on the bars. This is a good step to do whenever you think you have finished the toe settings for a given wheel.
Using a digital caliper measure from the rear of the rim to the string line, note the figure and repeat for the front of the same rim. If the front reading is smaller you have toe out. If the rear reading is smaller you have toe in. Get under the car, insert the toe eccentric into its place, use a 24mm wrench to rotate it about 30-45 degrees in one direction then go back and measure the rim to string line distances again. For zero toe, repeat this process until the front and rear edges of the rim are equidistant from the string line. When they are ---> Check the string lines are true. If the lines are true and the readings are equal (for zero toe) get back under the car and tighten bolt A & C as best you can to lock the alignment in place. Bolt B will get tightened up later when the wheel is off again because it is difficult to get to when under the car with the wheel on. It will also be possible to further tighten bolts A&C when the wheel is off again. It shouldn’t be necessary to keep a wrench on the toe eccentric when tightening bolt A but it will most likely be necessary to keep a 27mm wrench on the camber eccentric when you tighten its nut.
Note This guide does not cover detail regarding removal of underbody trays or parts not directly related to the alignment task.
Check the camber using the camber gauge and adjust via the camber eccentric on the base of the shock or camber plate if fitted. I usually set maximum camber on the base of the shock and refine camber using my aftermarket camber plates. Usually I have set this up before doing the string line adjustment for toe because it is somewhat easier to adjust the camber with the wheel off. If you do need to adjust camber at the base of the shock, loosen the lower shock bolt a little, then loosen the nut on the upper of the two bolts that secure the strut to the spindle. The upper of those two bolts is the camber eccentric and is rotated to make camber adjustments. When the camber is at the desired setting the lock nut for the camber eccentric should be tightened whilst the eccentric is held in place with another wrench. Tighten the lower strut bolt as well.
In reality I use this camber check only as a gross error check prior to setting toe which is the main purpose of the string line setup.
CHECK THE STRING LINES ARE TRUE once again and then check the toe at the front wheel. Most people will want zero toe or some amount of toe out depending on their driving application. Obviously for zero toe the wheel must have equal readings for the front and rear of the rim. For toe out the reading from the string line to the rim will be smaller at the front of the rim and larger at the rear of the rim. Prior to adjusting front toe it is advisable to lock the steering wheel in place and level using some timber or similar means. To adjust the toe, loosen the locknut at the tie rod end, then rotate the tie rod to pull the wheel in or push it out. Recheck the measurements between the wheel and string lines and repeat the process until the toe is set as desired then check the string lines are true and tighten the locknut against the tie rod end.
Repeat the entire process for the other side.
Re-attach the rear sway bar drop links to the sway bar and tighten the lower nut, Re tighten the rear sway bar drop link upper nut.
Lower the car back to the ground.
Remember to remove the rear wheels and tighten nuts A, B & C to lock the rear alignment in place. Tighten wheel lug nuts.
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