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General Disclaimer:
Front end alignment adjustments require a high degree of precision; failure to take this into account can destroy your tires in short order or, worse, make your car’s handling unpredictable/unsafe.
If you wish to change your car’s alignment, it is your responsibility to learn the concepts and alignment measurement methods to ensure accuracy and safe handling. Otherwise, have a shop do it for you.
OK, on with it, then…
ALIGNMENT INFO
The purpose of this post is to provide some of Saab’s specs, as well as relate my experiences with DIY alignment on a car used for autocrossing.
An advantage that c900s have over more contemporary cars is their double A-arm front suspension. Unlike newer cars with struts, which typically have toe adjustment only, the A-arm design allows you to easily muck about with your Saab’s caster and camber adjustments to greatly improve handling.
Saab’s stock alignment specifications are designed to ensure that the car understeers at the limit, which is easier to manage than oversteer. This is achieved with a positive camber spec.
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C900 alignment specs (excluding SPGs – sorry, Bentley manual not available for those specs, which are a bit more aggressive) are as follows:
. Camber: 2* +/- .5* positive
. Caster: 1* +/- .5*
. Toe-in: 2-6mm, measured at the rims
(Source: Saab Service Manual – Front Assembly Steering Device).
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My c900 tracks straight, road manners are decent, and tire wear is fairly normal and even (by even, I mean the wear pattern is the same on both sides of the car – the positive caster making the outer edges wear more than the rest of the tread). I thus concluded that alignment is likely within spec. From this point, I changed the alignment by adding more of the slender shims that are behind the upper A-arm’s mounting brackets.
There are three thicknesses: 0.5, 1.0, and 2.0 mm; your car will have come with several when it was aligned at the factory. You can get these shims off of any junker Saab. I have also used fender washers but they’re a bit of a pain (not recommended).
Adding shims makes the camber less positive/more negative by pulling in the top of the upper A-arm, which, in turn, pulls the top of the wheel in.
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Following is a list of shim thicknesses and their corresponding effect on camber:
. 1mm: changes camber .25*
. 2mm: changes camber .5*
. 4mm: changes camber .75*
. 5mm: changes camber 1*
. 6mm: changes camber 1.25*
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To change camber only, you would add the same shim thickness to both upper A-arm mounting brackets.
To change camber and caster simultaneously, you’ll need the table in the manual and I don’t have a scanner. However, caster changes apparently don’t have a huge impact on the alignment so...
WINGIN’ IT
When I played with my alignment to get more camber and caster, I took a fistful of shims and divided them up so I could install a stack in the front mounts that was half as thick as a stack in the rear (same amounts from side-to-side). To keep track of the car’s original shim set-up, I taped the new stacks together.
I don't know exactly what I ended up with but guess at least 1* negative camber; caster unknown. since I was playing with a non-daily driver, I didn’t really care about measurements – I just wanted more camber.
Now, more negative camber also increases toe-in, so I estimated how much to dial out the tie rods and made changes accordingly. Honestly, I just winged it here because I didn’t have time to actually measure the toe.
It turned out well, luckily – no horrible wear afterward.
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Following is a list of tie-rod turns and their corresponding effect on toe:
. 1/5 rotation: changes toe 1mm
. 2/5 rotation: changes toe 2mm
. 3/5 rotation: changes toe 3mm
. 4/5 rotation: changes toe 4mm
. rotation: changes toe 5mm
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Anyway, hope that’s helpful. If you want to spend $0, have a basic understanding of alignment stuff, and the techniques to measure it, then you should be able to DIY based on the shim and tie rod data above.
posted by 216.160.93...
, Fri, 7 Nov 2003 06:01:33, Fri, 7 Nov 2003 03:43:41
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