A correctly setup 928 should not hit the ground or float - in fact the handling should be very tight and surefooted. If not then Shock Absorbers, Springs and/or Ride height are the likely causes. Check the ride height before investigating the other more expensive options.
The Porsche 928 can suffer a multitude of suspension problems that basically stem from 2 factors. Firstly the car is heavy - most 928s weight over 3500lbs. Secondly the 928 is now a relatively old car.
The symptoms of problems are:
- the front of the car hitting the ground when either driving fast and/or over bumpy roads / speed bumps
- a floaty feel to the handling
The 928uk recommendation is to aim for 175mm front and rear. This is within the factory specification and will result in a very slight nose down stance.
A heavy sports car driven fast is going to make huge demands on its shock absorbers. Like all components shock absorbers have a limited 'life' after which there effectiveness weakens to the point that they should be replaced.
There are several options. If you don't intend driving your car hard then the standard shocks are totally acceptable. However if you want to push your 928 hard then nothing beats a set of sport shocks. This will give any 928 "SE/GT" standards of handling - with the downside of a more controlled ride which some might find unacceptable. For those that wish to adjust their setup then the ultimate option is a set of externally adjustable Koni shock absorbers.
As the 928 is so heavy its springs will gradualy sag under the weight and hence the cars ride height will lower. Whilst some like the lowered look there is no doubt that it brings the underside of the car nearer the road surface!
The inevitable result is that the underside of the car is far more likely to hit the road under extreme body movement because of fast driving or a very uneven road surface. In fact it can lead to speed bumps being impossible to drive over without scrapping the underside of the car. Not only does this cause a horrible noise but components of the car are damaged. The air conditioning is particularly vulnerable on all cars - as are front spoilers. S4 and later models are vulnerable to severe damage to their under engine belly pans.
The solution is to raise the car to its correct ride height
Sportier drivers may also wish to fit new springs or upgrade them to Club Sport specification (ie 10% stiffer at the front) or even fit aftermarket springs like those available from Eibach for the 928.
Suspension Sag
A common problem with 928s is "suspension sag". This is caused by the following factors:
- the weight of the car slowly shortening the springs
- mechanics working on the suspension and not re-setting the correct height
Sag leads to the following problems:
- Looks - while some people like the 'lowered' look, a car set to the correct ride height has a much improved stance and looks much "fresher".
- Handling - the suspension was designed to work at the correct ride height and performs much better set this way.
- Ride - it is surprising how much this is improved by setting a car to the correct height
Porsche specified ride height
The following specifications are from the Porsche 928 Factory Manuals:
- FRONT: an absolute maximum of 190mm with up to 20mm less perfectly acceptable. (This is effectively 180mm +- 10mm) There should be no more than 10mm difference from left to right. We recommend you aim for approx 175mm.
- REAR: is 173mm += 10mm. Again, no more than 10mm difference between left and right. We recommend you go for approx 175mm.
Tools
To change the ride height you will need the following tools - besides plenty of time and energy (its an exhausting job):
- 2" - 4.75" C spanner. e.g. Britool, tool number 3152
- a strong jack to raise the car
- wheel nut set
- torque wrench - to correctly re torque the wheel nuts
- strip of wood cut to approx 173mm long
Procedure
Step 1. Measure
First park the car on a completely flat surface. A level double garage floor is ideal, provided there is enough access around the whole car.
- Lie underneath the car with the measured strip of wood.
- Measure front and rear as follows
Step 2: Adjust
- Jack up a corner of the car (remembering to use the correct jack points in the car body)
- Remove the wheel to gain access to the suspension
- Adjust the notched nut right to raise and left to lower. As a guide: approximately 8 complete turns equals 1 inch.
- Replace the wheel and correctly torque the wheel nuts
- Move to the next corner of the car until the car is fully adjusted.
Step 3: Settle
When the car is fully adjusted you will notice that it sits very high. This is because the 928 suspension takes time to settle to its actual ride height. Therefore the suspension must be forced to settle before the height can be re-measured and checked.
- Take the car for at least a 5 mile drive to settle the suspension.
Step 4: Repeat Until Correct
- Repeat steps 1 to 3 until the ride height meets the factory specifications detailed above.
Note:
Some procedures call for the wheels not to be removed and the car not to be jacked up. This does mean that the height can be re-measured straight away without a drive, removing the wheels; and could be quicker. However, the notched nut is difficult to move (especially on the front) and we recommend this procedure to get the necessary leverage required.
The measuring point is directly behind the centre of the wheel hub, where the suspension attaches to the car. (For S4 and later cars it is just in front of the under belly pan - as can be seen at the upper left corner of the picture above).
The actual point is the flat machined surface between the two flanges and two bolts. You should be able to hold the strip of wood vertically between the ground and the machined surface with a few mm to spare (for a 175mm front ride height).
The measuring point is located at the end of the horizontally "U" shaped suspension arm, where it is attached to the car.
The actual point is the small raised flat surface. You should be able to hold the strip of wood vertically between the ground and the machined surface with a few mm to spare (for a 175mm rear ride height).