There are two basic types of classic VW suspension setups (not including Bus models), these are IRS and swing axle.
What are the differences?
The difference visually is most obvious when removing the engine or excessively lowering a vehicle. The "camber" effect is much more severe on Swing Axle vehicles as they have a single pivot point at the gearbox, meaning the relative position of the wheels in relation to height will dictate the camber of the wheel. I.e. gearbox low (lowered vehicle adds negative camber, raising it up adds positive camber.)
IRS rear ends reacte differently in that the camber of the wheel is mostly dictated by the fixing point of the irs to the gearbox/ torsion bar tube joint which is fixed from factory. Now when lowering or raising and IRS pan, positive and negative camber will still occur it is not for the reasons stated above, and is minimal in comparision.
Mechanically the differences is that swing axle suspensions actually use the axle as a suspension component, whereas IRS used the combination of the spring plate and arm and the suspension components and the only function of the axle is to deliver power:
Want to dig a little deeper?
1: Swing Axle
2: IRS (Independent Rear Suspension)
Is available in two configurations
1: Single spring plate type
2: Twin spring plate type
Note that the IRS spring plate is a lot shorter than the swing axle. Make sure that you differentiate whether your IRS has the twin plates or just the single. That’s all there is to it! Well not exactly. It turns out that different years of vehicles used different lengths of torsion bars. But only three:
1: 21 3/4” (Torsion bar does not stick out)
2: 24 11/16” (Torsion bar sticks out about 3”)
3: 26 9/16” (Torsion bar sticks out about 5.5”)
So that’s it. All that you need to know to order the right set of Drop / Raise Plates is your suspension type and the length of your torsion bars.
Years / Compatibility
The following is only accurate for US models:
• Anything after 1968 that is an an air-cooled suspension (411 models excluded) is IRS.
• Models up to 1958 were only swing axle and used 24 9/16” length torsion bars.
• 1958 to 1968 bugs were all swing axles and used 21 3/4” length torsion bars.
• Type 3s used 24 11/16” length torsion bars up to 1968.
• 1969 and later models (Things excluded) used 26 9/16” length torsion bars and were all IRS.
• All IRS models up to 1973 used twin spring plates. After 1973 all models were IRS using only a single spring plate.
• Thing Models were all IRS and used 24 11/16” length torsion bars.
- See more at: https://www.limebug.com/how-to-guides/view/39/#sthash.lAf75zQX.dpuf