Before you choose your spring, you need to understand the difference between Medium duty and Heavy duty. First off the difference has nothing to do with ride quality. Our Heavy Duty spring will not give your Bronco a stiffer ride. This is simply to make sure your Bronco will sit level or at the very least not squat in the back when your Bronco is complete.

Medium-Duty springs are for 66-77 Broncos that have very few add-ons or accessories in the rear. For example, if you have a stock half cab or roadster you would choose medium duty. If you have a resto-mod wagon with a soft top, stock rear bumper, no spare tire, and stock fuel tank, with or without a back seat but not typically using it, then you also would choose medium-duty springs. We do NOT recommend medium duty for trailer towing.

Heavy-Duty springs are for 66-77 Broncos that are geared more towards a well-equipped resto-mod for on and off-road use. If you have or plan on upgrading to a 20+ gallon rear fuel tank, tire carrier + tire, steel plate rear bumper, and/or want to run a hardtop, the heavy-duty leaf spring is also a great choice for your build. These are also the best option if you plan on ever towing anything with the Bronco. If you like going off-road and hitting the trails, the heavy-duty leaf springs are typically the best option for you as well.

For some of you, there will be some combination of parts that accessorize your Bronco in between a soft, medium, heavy, and extra heavy-duty setup. This is why we offer lifted spring perches, 1/2" and 1" lift blocks as well as pinion shims for driveshaft angle corrections to get your ride height and driveability spot on. Our new 1/2" lift block will also offer the option to move the axle back for that perfect amount of tire to fender clearance for the uncut lifted 66-77 Broncos.

Installation Note: The Double spring Wrap aka Military wrap is to be installed towards the front of the vehicle.

You can also add on great upgrades when purchasing these springs like Leaf spring and shackle mounting hardware, Shackle bushings, the Duff HD spring plates, U bolts or HD U- bolts (both that come standard with new HD hardware), HD shackles, pinion shims, lift blocks and new Duff HD weld on spring perches offered in factory and 1" built-in lift.

Choose a Drop Bracket or our Axle Raise Bracket for your system. This will allow for the correct geometry to match our steering system.

Drop Track Bar Bracket - Welds to the frame near the steering gearbox.

Axle Raise Bracket - Welds to the axle and raises the track bar off the axle mount, we prefer this option as it takes stress off the frame and minimizes the potential for bump steering.