The H&R 51657-77 is a Super Sport lowering spring for the 07-10 Ford Shelby GT500 and GT500 convertible V8. All H&R OE Sport Springs, Sport Springs, Super Sport Springs are progressive when possible for the application. That progressive design is the main reason to choose it over a generic straight-rate spring. Owners on user forums describe a level stance and a ride that feels better than stock, and one reports that the rear springs also cut down wheel hop. Compared with cheaper budget springs, it suits a driver who wants a clean drop and street comfort on a V8 Mustang.
Published application details differ, with some sources listing only 2007-2010 and others extending coverage to 2014, so confirm your exact model year and body style with the manufacturer before ordering. Lowering also changes suspension geometry. Alignment should be checked after any suspension ride height modification. One forum member also recommends an adjustable panhard bar to keep the rear centered. For DIY-minded buyers, rear-only swaps are the easiest entry point. An owner who tried this on a Shelby GT500 said it will take about a 1/2 hour to install these. Search terms this part targets include GT500 progressive lowering springs, 2007-2010 Shelby GT500 convertible springs, H&R 51657-77 rear level, and GT500 rear spring install.
The manufacturer says H&R springs install the same way stock springs do. If both ends look alike, the closer coils go up. If one end is smaller, match the factory orientation.
Owners on user forums report that rear-only H&R sets leveled their GT500s, and some kept the stock fronts without issue. Results depend on tire size, so check ride height before and after.
The manufacturer recommends checking alignment after any ride height change and following the factory service manual specifications.
Rear springs are the more approachable job for a home mechanic. Plan on jack stands, a floor jack, a torque wrench, and a penetrating lubricant for stubborn fasteners. Front springs involve strut disassembly and spring compression, so follow the factory service manual and take photos of bolt thread positions before removing anything. Measure ride height before and after the install, and schedule an alignment once the work is done.
