In my last blog entry, I wrote about my challenges with oversteer during my time attack event. In doing a lot of research since that event, I discovered that the extreme oversteer that I experience could happen to anyone driving their 9-5. The Saab 9-5 rear suspension design incorporates more than twice the number of rubber bushings as the front. That’s double the places that can wear out and create excessive slop and movement in the suspension. When the bushings begin to wear out, wheel alignments no longer hold, and things go south.
The rear suspension uses 3 different control arm bushings, labelled in this diagram as #7 (4566378 click here to view), #15 (4567244 click here to view), and #17 (12781136 click here to view). The most common culprits are the upper #15, and #17 for wear. If you’re experiencing excessive negative camber, then #15 is your problem! Camber shims are often prescribed as solutions to this, when the real issue lies in the bushings.
When #17 exhibits wear, cornering forces cause the bushings to over deflect and lose proper wheel alignment. This creates a sense of “rear steering” as the rear toe changes: leading to increased tire wear, added stress on the chassis, and at higher speeds and higher loads snap-oversteer. #15 contributes to the problem, and as a result should be changed at the same time.
When you enter a corner, the bushings deflect and absorb some of the forces. If the bushings continue to deflect there comes a point where the rear toe is changed enough that your tires can no longer handle the lateral loads being demanded. As the tires reach this threshold, there is a sudden release of traction and the rear tires will immediately begin to slide out. If you don’t react quickly, have never experienced oversteer, or don’t know how to correct it: you could be in a lot of trouble on the road. And probably end up off the road.
The best and only way to combat this issue is to replace your bushings before problems arise. If your vehicle has excessive rear camber, has ever experienced snap-oversteer in poor conditions, or you don’t know when the bushings were last replaced (with 80k+ miles on the vehicle): it’s time to get them replaced.
Powerflex makes really nice polyurethane bushings for #17, and once installed will never need to be replaced again (all Powerflex bushings feature a lifetime warranty). Available in both Street (PFR66110X2 click here to view) and Black Series (PFR66110BX2 click here to view) polyurethane, they will make a significant improvement to the feel of your suspension. I myself will be picking up the Black bushings for the race car. #15 is available as a direct OEM replacement, and a set of new rubber bushings will bring your rear alignment back into spec (a full alignment is recommended with any suspension work performed). For the price of all 4 replacement #15 bushings, it’s a no brainer to get the suspension working like new again.
Powerflex bushings provide ultimate durability
The #7 inner bushings are far less likely to be an issue, and due to their location require a lot more work to replace them. If you or your mechanic are already planning work in the area, I recommend replacing these bushings regardless if they’re ‘needed’ or not. In my searching, I didn’t find many examples of the rear subframe bushings needing to be replaced, unlike the front subframe bushings which are a very common point of wear.
With all this talk of rear suspension, the front is not to be overlooked. eEuroparts just posted an excellent video demonstrating the effects of worn out front subframe bushings which can be found here:
Powerflex also offers a bushing kit for the subframe, and both bushings used on the front control arms. These bushings are a major step to restore and improve the exceptional way your 9-5 handles on the road, and how it feels during cornering. A sloppy, and boat like suspension is no good for the race track, and it’s useless for safe driving on the street!
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