I'm thinking of installing the Ford Motorsport springs on my 91 LX. These lower the front 7/8 and the rear 1/2 (I think). Do I need to worry about my steering geometry or bump steer at all? Also, should I wait and get some caster/camber plates and do those at the same time or is it okay without them?
with that amount of lowering, the answer is no, you do not need to worry about bumpsteer. As far as CC plates, with that amount of lowering, I don't think you need them. You *might* need to get creative with your alignment by filing out the bolt holes on the stock setup to get your camber to spec, I know JD (who posts here) has done this.
I have CC plates and bumpsteer correction, but I also have lowered my car 1.7" and added a lot of positive caster, requiring CC plates.
Vic is right; with less than 1.00" of front-end drop, you'll be able to easily dial in the camber by just elongating the strut tower mount holes with a small, round metal file. CC plates are not needed for this kind of application. Any more than 1.00" of front end drop will probably also require a bumpsteer kit. Max Motorsports and Steeda both carry excellent products to correct this.
If however, you wish to dial in additional caster (more than +4.00 deg.), or wish to add some cross-caster, CC plates are required and recommended.
I will tell you however, others here have installed FMS 5300-C springs with disasterous results. Some report a near 2.00" drop on Fox mustangs. Some report uneven rear spring height, requiring cutting the springs. Quality control seems to be a problem with this item. They are also very stiff, and will require upgraded shocks/struts - stock shocks will not work well at all.
Cindy has these installed on her '96 GTS, and she loves them. Drop her a line and see how she had her's set up.
Thanks for the input. Kinda scary about the consistency of the products... Do you have experience with any other springs out there? I don't want to drop the car more than 1" but I would like a slightly stiffer spring.
The biggest "bump steer" problem in Mustangs is the SOFT stock steering rack bushings. No matter how much you lower it, the "bump steer" will be a fraction of that induced by the excessive deflection of these bushings. Replace them with polyutrethane or aluminum and forget about "bump steer".
Check my website for information on other aftermarket spring configurations; I have quite a few listed, and this can very helpful to anyone considering making such a radical change.
If all you're after is crisper cornering and better control, perhaps a different set of shocks is all you need? Some allow the driver to adjust the firmness of both compression and rebound. Others here can suggest something along those lines; I don't have much experience with aftermarket shocks.
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