The radius arm (also known as the strut arm) is a key component of a Bronco's front suspension. There are two of them that secure the front axle in place under the Bronco; they attach around the axle-tube wedges and bolt to the frame. Understanding what a radius arm is, how it mounts and functions, is a key part of choosing the right suspension lift system for your '66-'79 Bronco or F-150 4x4.

Stock radius arm: The stock radius arm for all Broncos and 1/2-ton 4x4 Ford Trucks was the same design from '66-'79 - the Big Broncos and F-150 4x4's of that era had the same radius arm as the 1st-generation Broncos. This Ford OEM part left a lot to be desired in terms of suspension travel, control, and ride quality once lifted. It is also as prone to rust as the rest of the vehicle, and after 45-55 years of use the end that attaches to the frame (a threaded shank where the control bushings ride) is where rust loves to eat away the arm's strength and integrity. Push the arm hard enough and they can bend. This is why James Duff Inc. completely redesigned it.

T-Rex arm: A stock-length radius arm designed and manufactured by James Duff Inc. It bolts in place of any factory radius arm on a '66-'79 Bronco and F-150 4x4. It is a tubular and plate-steel design that uses a secondary cast-steel head unit to mount it to the Bronco. This two-piece design makes install easier and incorporates 4.25 degrees of added caster - and when it comes to lifting Bronco front suspension, caster is king. It is massively stronger, offers more caster than OEM, and allows up to 37″ tires without sacrificing the Bronco's tight turning radius. Matched with our coil springs and shocks you get the best ride quality and control.

Extended Long-Travel Radius Arms: Matched with our long-travel systems, these allow the Bronco to traverse almost any terrain. Same tubular/plate-steel + cast head-unit design, with 4.25 degrees of added caster, massively stronger, and allowing up to 37″ tires. Offered for every year Bronco from '66-'96 and popular for solid-axle-swapped Ranger-based vehicles; a direct fit for all Dana 30 and 44 axles made from '66-'79. Kits available for: 66-77 Bronco, 78-79 Bronco, 73-79 F-Series Truck, 80-96 SAS Bronco, Ranger-based-vehicle SAS Bronco, and custom applications.

*Frame mounts and hardware in these kits are universal; modifications to fit your vehicle may be required.

NOTE: Arm geometry, ride control, and caster are all greatly affected by lifting a '66-'79 Bronco and F-150 4x4. Any lift over 3″ for a 1st-gen Bronco, and any lift over 4″ for a 2nd-gen Bronco or '66-'79 F-150 4x4, may require more caster correction than stock-length aftermarket arms and C-bushings provide. Extended radius arms, radius-arm drop brackets, and caster/camber-correction bushings could be necessary. Results will vary - see your alignment shop after you install the lift.

Our radius arms are designed and engineered to work with the factory-equipped Dana 30 or Dana 44 front axle on the Early Bronco platform. They will also work in the full-width high-pinion Dana 44 that comes installed in the '76-'79 F-150 4x4 or '78-'79 Big Bronco. If you want to pair them with another axle such as a Dana 60 or Super Duty 60, you must ensure the axle uses Ford-style axle wedges, or you must grind off any brackets that use a different attachment style and weld on the wedges we sell.

For straight-axle vehicles, caster is a major part of the front-end alignment equation that makes your front axle and steering wheel track straight while driving. Without the right degree of caster, you are constantly correcting the steering wheel and have little confidence in your ability to control and enjoy your Bronco.

The right amount depends on tire size, lift size, and vehicle. On '66-'77 Broncos and pre-'76 F-150 4x4's with factory low-pinion Dana 44 front axles, too much caster can cause front driveline failure prematurely. With that in mind, we shoot for a minimum of 3 positive degrees of caster in the front axle. High-pinion Dana 44 front axles can handle up to 3 more positive degrees but also do very well at a total of 3 degrees positive. Your front-end bushings, steering geometry, and toe-in are also important here.

NOTE: Any lift over 3″ for a 1st-gen Bronco, or over 4″ for a 2nd-gen Bronco or '66-'79 F-150 4x4, may require more caster correction than stock-length aftermarket arms and C-bushings provide. See your alignment shop after you install the lift.

1966-77 Bronco with stock arms:

• #6002 - 2° C-bushings, stock height
• #6004 - 4° C-bushings, 1-2″ lift
• #6007 - 7° C-bushings, 2.5″+ lift

NOTE: Any suspension lift over 2.5″ on a factory-equipped 66-77 Bronco may require radius-arm drop brackets or aftermarket radius arms to achieve the 3+ degrees of caster required for control at road speed.

1966-77 Bronco with #5350 Long Travel Radius Arms (4.25° built in):

• 3.5″ lift: #6004 4°
• 5.5″ lift: #6007 7°

1966-77 Bronco with #5355 T-Rex Radius Arms (4.25° built in):

• 2.5″ lift: #6004 4°
• 2.5″ lift with high-angle drivelines: #6007 7°
• 3.5″ lift: #6007 7°
• 5.5″ lift: #6007 7°

78-79 Bronco/F-150 with #5351 Long Travel Radius Arms (4.25° built in):

• 2-4″ lift: #6002 2°
• 5-6″ lift: #6004 4°
• 6″+ lift: #6007 7°

78-79 Bronco/F-150 with #5355 T-Rex Radius Arms (4.25° built in): same as the #5351 chart above.

80-96 Bronco SAS with #5353 Long Travel Radius Arms (4.25° built in): same as 78-79 Bronco with #5351, but will vary depending on what degree the C-wedges are welded onto the housing.

Bronco II & 83-97 Ranger Dana 44 SAS with #5352 Long Travel Radius Arms:

• 3-4″ lift: #6004 4°
• 5″+ lift: #6007 7°

A performance-oriented suspension and a smooth ride - our progressive-rate coils offer the best of both worlds. Unlike a stock single-rate coil, the rate gradually increases as the coil compresses: the upper wraps are softer for a more comfortable street ride, the middle rates are firmer to handle bumps and dips without jarring, and the last few wraps are a higher rate to control up-travel and prevent bottoming out.

Because the coils have a softer initial rate they also deliver more suspension travel than a single-rate coil. The softer rate helps the tires stay on the ground for better traction and handling, and the progressive nature helps keep the vehicle flatter in corners and limits body lean.

Stock suspensions were designed primarily for improved road use and safety with little consideration for true off-roading. Our customers are outdoor adventurers who travel the back roads and beyond, and we consider that type of use and on-road safety when designing our suspensions.

A suspension lift raises the frame and body from the differentials and wheels, allowing larger tires and increasing ground clearance under the axles to clear trail obstacles. Attention to wheel travel and overall ride quality is an important consideration in our lift designs - improved traction and wheel travel directly translate into how well a vehicle traverses any terrain, and a vehicle properly equipped for off-road use causes less damage to our trails.

Our shocks are valved 70% rebound, 30% compression. With our systems, our proprietary coil and leaf springs are engineered so the shocks aren't needed for primary compression control - our shocks smooth out the ride by predominantly controlling rebound, and they don't overheat because they aren't trying to control compression.

Conventional 50/50-valved shocks use equal pressure on both compression and extension. That creates a choppy ride and overheating shocks as they try to control compression instead of letting the spring do its job.

The only time we have seen 8 of our classic 70/30 shocks create a rough ride on a Bronco is when the Bronco had very few accessories on it, or was a stock roadster (U13) or half cab (U14). Even then it was not rough across the board, since several other factors create a rough ride - overinflated tires, stock or worn-out seats, poorly installed suspension, other companies' suspension combined with Duff shocks, and sometimes personal preference.

The biggest misconception in the industry is that all off-the-shelf twin- and mono-tube off-road shocks have the same 50/50 valving. At James Duff that couldn't be farther from the truth. We developed a shock over 30 years ago that lets our springs do their job and spends more time controlling rebound - which is why you can run 8 Duff classic 70/30 shocks and still get a smooth ride. Eight shocks also help control body roll, especially when lifting over 3″.

Duff suspension components are designed, tested, and mostly built in house. Our design team strives to build the highest-quality parts while keeping the customer's budget in mind. Our components are built for easy installation using common hand tools, and most require little or no welding. Our systems are predominantly built using the best American-made materials available - many parts are CNC laser cut and bent for a precision fit, formed and welded on-site by our fabrication specialists. Unlike others in the industry, we use a premium durable powder coat or high-luster zinc finish for longevity.

95% of Duff products will match some sort of factory mounting spot on the vehicle, usually to locate where a bracket goes. You will use the bracket as a template to drill the rest of the mounting holes, and we usually recommend welding the brackets into place (or vice versa) depending on what you have access to.

Please take into consideration that although we strive for proper fitment and build our products in fixtures for consistent accuracy, the majority of vehicles we work on are over 30 years old (some over 45), so there will be some inconsistencies from vehicle to vehicle. It may take a couple of hits with a big hammer for perfect fitment. 🙂

Dana 30 front axles came on Early Broncos from '66 to '71.5. They are easily identified by looking at the top of the steering knuckle: if your axle has a cap with 4 bolts, it is a Dana 30. Dana 30's used king pins to attach the knuckle to the axle.

Halfway through 1971, Ford upgraded the front axle to a Dana 44. To identify it, again look at the top of the steering knuckle: there will be a ball joint with a single castle nut attaching it to the threads on top of the ball joint. If yours has a ball joint, it is a Dana 44.

No, we do not offer the piece that goes between the arm and the axle as a stand-alone part.

The easiest way is to assemble the front end first using the factory radius-arm mounts on the frame as your starting point. Set the frame up on big jack stands (or saw horses) on each end so it is level. Once the front end is completely assembled minus the coil springs, mount the front wheels with the tires you plan to run and make sure they point straight forward. Set the frame-to-axle height for your desired lift and center the front axle under the frame.

Now set up your rear axle where you want your wheelbase to be (a couple of plumb bobs are your friend here). Set the axle at the same height as the front, tilt the pinion angle up 13-15 degrees, then square the axle housing to the frame, tack-weld or bolt the truss onto the axle, and assemble the links. Attach the links to the frame brackets and, with a helper, install the frame brackets to the frame with a couple of giant C-clamps, then adjust the link lengths until they bolt to the truss. (The pinion angle is a general guideline for stock EB driveline configurations and could change depending on drivetrain.)

The location for the coil buckets presents itself once the 5120 lower coil retainers are installed to the truss. Use plumb bobs to make sure the coil buckets are centered on the lower coil retainers, then tack-weld the buckets so the bottom of the bucket is flush with the bottom of the frame. We don't recommend fully welding the buckets until the entire Bronco is complete, so make the welds a heavy tack. See our Extreme 4-Link and Dual Sport 4-Link install instructions for more.