My suggestion is you have 90K on the back just like on the front so they all should be replaced. Also remember, this aids in the proper control and handling of your vehicle not just on bumps, but also in turns and provides a stable ride going straight.
If the front is done and not the back the vehicle may not handle or ride as well not to mention it may handle a little more unsafe in hard turns etc.
So my suggestion is definitely all 4.
As for how hard - depends on your mechanical ability. Since I don't know it is hard for me to say. You need to be careful as you will be having the car on jacks and you need to have a basic understanding of what the components attach to what so you don't hurt yourself. The struts connect the body to the frame. Disconnecting something that isn't properly supported may cause equipment damage or worse, personal injury or death. So again, not knowing your skill level I would not be able to tell you. Also, taking the springs apart. If not properly compressed damage or injury can happen.
Special tools, definitely spring compressors then various metric tools.
Replacement of what...........my suggestion......only because I have had to take things like this apart SEVERAL times. Replace all the components. It will save hours of troubleshooting noises, components wearing out and having to reaccomplish and money. On several vehicles I have had to have the front end lined up several times due to taking things apart several times. Not worth the time and money to redo. Fix it right the first time. All the components have been on there for 90k and the all do different things. So replace them.
Example on the front, not just the strut but the coil spring bumper, coil spring seat, coil spring insulator, strut mount bearing support and the strut mount.
I have attached a pic showing the front end components. This is for a 2001 Saab 9-3 L4-2.0L Turbo (B205). If you want your vehicle specific I would need to have you tell me the specific 9-3 and the specific engine.
Hope this helps!
Monday, November 17th, 2008 AT 11:26 PM