AVANT S4 KING
01-03-2006, 09:08 AM
Walter: Thanks again for your insistence in the thread below. I found several bits of info on the net about Audi's 4-Link suspension system and I figured I'd post the best one I found for the benefit of the AW.
<a href="http://www.babcox.com/editorial/bf/bf100074.htm">read me</a>
Heres the Audi specific info:
AUDI A4 & A8 AND VW PASSAT
These vehicles get the award for the most complicated suspension geometry that's on the road today. The 4-link front suspension has more arms and joints than an octopus (two upper and two lower ball joints on each side, with split upper control arms on top), and uses a "virtual steering axis" to maintain zero caster regardless of the steering angle.
The idea behind this unusual setup is to cancel out all torque steer and to provide extremely precise handling. It works great, but requires special alignment software to handle the caster and SAI readings. So if you haven't updated your alignment equipment since 1997 when this suspension was introduced, you're going to get weird caster and SAI readings.
Actually, you don't need caster or SAI readings because they have no meaning on this suspension. There are camber specifications, but no factory adjustments for correcting individual camber if it is out of specifications. Even so, you can shift the engine cradle right or left to add camber to one side and subtract it from the other.
Toe is adjustable, but there are actually two different toe settings and you have to use the correct procedure or you'll get yourself into trouble. Ordinary toe, which Audi called "unladen toe," is measured in the usual way. If any corrections are needed, they must be made at the inboard end of the tie rod, not the outboard end. Both ends of the tie rod are adjustable, but the outer end is not for ordinary toe adjustments. It changes the angle between the tie rod and steering arm, which Audi refers to as "raised toe." Adjusting this second toe angle requires a special tools (VAG 1925 & VAG 1925/3) and a special procedure.
To check or adjust raised toe, the VAG 125 tool is attached to the subframe. The vehicle is then raised and lowered on the VAG 1925/3 adapter tool. The tool holds the suspension in a slightly raised position so toe can be measured again. There should be 12 degrees more toe-in on each side than before. If not, the outer tie rod end needs to be adjusted until the specified difference in toe readings is obtained.
<a href="http://www.babcox.com/editorial/bf/bf100074.htm">read me</a>
Heres the Audi specific info:
AUDI A4 & A8 AND VW PASSAT
These vehicles get the award for the most complicated suspension geometry that's on the road today. The 4-link front suspension has more arms and joints than an octopus (two upper and two lower ball joints on each side, with split upper control arms on top), and uses a "virtual steering axis" to maintain zero caster regardless of the steering angle.
The idea behind this unusual setup is to cancel out all torque steer and to provide extremely precise handling. It works great, but requires special alignment software to handle the caster and SAI readings. So if you haven't updated your alignment equipment since 1997 when this suspension was introduced, you're going to get weird caster and SAI readings.
Actually, you don't need caster or SAI readings because they have no meaning on this suspension. There are camber specifications, but no factory adjustments for correcting individual camber if it is out of specifications. Even so, you can shift the engine cradle right or left to add camber to one side and subtract it from the other.
Toe is adjustable, but there are actually two different toe settings and you have to use the correct procedure or you'll get yourself into trouble. Ordinary toe, which Audi called "unladen toe," is measured in the usual way. If any corrections are needed, they must be made at the inboard end of the tie rod, not the outboard end. Both ends of the tie rod are adjustable, but the outer end is not for ordinary toe adjustments. It changes the angle between the tie rod and steering arm, which Audi refers to as "raised toe." Adjusting this second toe angle requires a special tools (VAG 1925 & VAG 1925/3) and a special procedure.
To check or adjust raised toe, the VAG 125 tool is attached to the subframe. The vehicle is then raised and lowered on the VAG 1925/3 adapter tool. The tool holds the suspension in a slightly raised position so toe can be measured again. There should be 12 degrees more toe-in on each side than before. If not, the outer tie rod end needs to be adjusted until the specified difference in toe readings is obtained.