About a year and a half ago with 16K miles on the odometer I had a set of SR lowering springs and an adjustable pan hard bar installed on my 2012 GT Mustang. I didn't change the struts because the car had the Brembo package so they were already an upgrade over stock. The car handled and drove excellent - much better than the Brembo set-up - until about 3 months ago. I'm now at 30K miles and it still tracks straight and I have no unusual tire wear, but the motion of the car traversing bumps and dips has changed significantly. The tires seem to slam over expansion joints and pot holes that compress the suspension where before it seems to absorb the jolts. And if I traverse something that makes the suspension expand like a heave in the road it feels like the tires have left the ground. The old "rock the car" test to see if your struts/shocks are worn would indicate they are not. The car settles out very quickly. Any ideas on what is causing this?

 

Sounds like you blew out your struts and shocks. When you install lowering springs, you need struts/shocks that can support the springs.

Spring performance failure point is further than their physical failure point, meaning they will break/chip/crack before they begin to lose their compression rate.

 

Shocks. Absolutely shocks.

 

The Brembo equipped shocks are identical to the base GT's, just slightly revised valving, otherwise identical "quality" and materials between them.

Additionally, shows don't need to be leaking oil externally to be excessively worn internally. I'm not sure what causes the stock dampers to wear out so quickly, but I suspect piston material, oil quality, or shock body, or maybe a combination of all, allowing the fluid to pass around the piston easier providing less compress and rebound control.

I also suspect the SR lowering springs caused quicker shock wear. Lowering springs force the stock shock piston to work inside an smaller overall average travel area, coupled to higher spring rates, works the piston and oil harder.

If you don't want to drastically change how the car rides, replace them OE Ford shocks with some KYB GR2's or Koni STR.T's. If you want to firm up the ride over what you previously had without requiring more aggressive spring rates, look into Bilstein's. I would only recommend Koni's if you plan to take the car to some track events, as many have found them too stiff from daily drivers, though it depends which springs are coupled with them.

 

Yep, springs don't really "wear" out.


Look at a set of Bilstein dampers or Koni.