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  • JP Magazine
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  • Four Wheeler

Pro Comp’s Long-Travel Suspension For TTB Ford Broncos And F-150s

Posted in How To: Suspension Brakes on December 13, 2016
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It’s always fun to read about lift kits being installed on brand-new 4x4s. But there’s a large number of readers who are starting out with rigs destined for weekend four-wheeling that are far less pristine and way less expensive than iron that’s just rolled off the showroom floor. We’re talking decades-old 4x4s with odometers that are on their third lap and stock suspensions that haven’t seen a mechanic’s wrench or grease gun in a quarter century. Rigs like these, which can be purchased for a couple thousand dollars, make excellent trail projects. Mid-’80s through mid-’90s Ford F-150s and Broncos are perfect examples of such finds.

The fullsize Broncos, which share the F-150’s platform and Twin-Traction Beam (TTB) suspension, are becoming especially popular because they are roomy and abundant, making them a very good candidate for anyone who wants to build a decent family trail rig on a limited budget.

Fit For The Trail

One of the key factors for making TTB Fords more adept at moderate levels of off-road driving is improving ground clearance. That’s done by stepping up tire size. The stock suspension can accommodate 32-inch tires, usually without fender-clearance issues, but the tire will rub on the radius arms. When 33s are run there’s minor fender issues under extreme suspension flex. That’s where upgrading the suspension comes into play.

A 4-inch suspension lift is ideal for TTB-era Fords that are going to be used primarily as a daily driver and weekend four-wheeler tackling light to medium off-road exploring of the desert, mountains, or backcountry. Such a lift allows the use of 33s without any clearance or rubbing issues—and one could run 35s with minor fender trimming.

Pro Comp’s 4-inch Stage II TTB suspension at work under our ’91 Ford Bronco.

Long-Travel Benefits

Some TTB suspension kits use drop brackets to lower the radius arms and the axle beams, while retaining the factory radius arms. A better solution for both ride comfort and trail performance is replacing the factory radius arms with longer and stronger versions.

The benefits of a long-travel TTB suspension is the longer radius arms increase suspension flex and increase ground clearance while improving the TTB’s strength and durability. Although such kits cost more than those that retain the factory radius arms, the improvement in overall suspension performance is worth the cost. That’s why we opted to slip Pro Comp Suspension’s Stage II (PN K4054B) suspension under our ’91 Bronco instead of a less expensive kit. The kit’s racing-influenced technology and engineering show in the tubular radius arms that are nearly 15 inches longer than the OE versions. Pro Comp’s radius arms are considerably stouter, too, so they could take the stress of extreme flexing during off-road excursions.

The kit comes with Pro Comp’s ES3000 shocks and an add-a-leaf or lift block for the rear suspension. For this truck, we didn’t want to use lift blocks and our old Bronco’s rear leafs have more than 200,000 miles on them so add-a-leafs aren’t going to give us the full 4 inches of lift. Our solution: replace the old springs with Pro Comp’s 4-inch leaf springs (PN 23211).

Mid-’80s through mid-’90s Ford F-150s and Broncos are ideal candidates for suspension upgrades that make them trailworthy family four-wheelers.

On The Lift

Doing a TTB suspension upgrade can be done in your driveway, but it’s definitely not recommended. You really need a hoist to do the work. Better yet, have a shop that has a lift, air tools, and expertise handle the install, which is about a 12-14 hour job. We turned to Dunks Performance in Eugene, Oregon, to handle our installation.

The rear suspension is a piece of cake. The front, however, requires a lot of grinding and drilling to remove the factory TTB brackets in order to replace them with the new drop-down bracketry. The longer radius arms require relocating the rear hangers on the framerails. Pro Comp’s instructions are excellent, and the kit has all the hardware to do the job without interruption.

Our Eddie Bauer–model Bronco came with factory optional dual shocks in the front, which required ordering a second pair of ES3000 shocks. Installing the longer front coils and new shocks is pretty straightforward. Be forewarned that some of the nuts and bolts on a suspension this old are going to be buggers to get loose. Have plenty of penetrating lubricant and muscle handy!

Nonetheless, it’s all worth the effort when it’s done. The highway ride and handling of our Bronco is night and day better than it was before we started. The off-pavement performance is also remarkably better; the suspension flex gives our old Ford nearly 15 inches of front wheel travel, which is considerably more than the old girl had in stock form.

Now we are able to run 33-inch Pro Comp A/T Sport tires without fear of body clearance problems or rubbing on the radius arms when we need lock-to-lock turning ability. The taller tires have also given us another 2 inches of ground clearance. That’s a good combination to have for our mild- to moderate four-wheeling needs.

Should we want more lift down the road, the Pro Comp brackets are already set up to easily change to a 6-inch lift. All we need to do is drop the beam’s center ends to the lower bracket hole and swap in longer springs and shocks.

Scott Blanchard, the suspension tech at Dunks Performance, went about the task of removing the old front suspension components to make way for the Pro Comp parts. A lift and air tools are a must for this installation. One bolt that was particularly difficult to break loose was the one holding the radius arm to the passenger-side axle beam. The bolt had rusted to the inner nut. An 8-foot cheater bar eventually broke it free.
The stock radius arms were removed and discarded, as were the OE brackets that held them to the framerails. Pro Comp’s race-inspired long-travel Stage II radius arms (bottom) are 15 inches longer than the OE arms, providing more suspension travel and articulation. The new tubular arms are also much stouter than stock.
Blanchard used multiple ratchet straps and adjustable jackstands to support the TTB front axles when installing the new components. Adjustability makes the alignment of the radius arms and beams to the drop brackets easier.
The OE passenger-side radius arm bracket was bolted to the frame, but it was easy to remove. The new bracket was located farther back.
The OE driver-side radius arm bracket was both bolted and riveted to the framerail, which required the use of a grinder to remove it.
Mounting the new radius arm brackets required relocating them exactly 15 inches rearward of the OE brackets per Pro Comp’s instructions. On some models, like ours, there was a convenient hole on the bottom of the framerail that lined up 15 inches from the second forward mounting hole in the old bracket.
Blanchard drilled 7/16-inch holes in each side of the frame to mount the new radius arm brackets.
Tip: Be very careful when drilling the frame for the driver-side bracket as there are fuel and brake lines running behind the framerail.
Pro Comp’s kit comes with all new hardware along with torque specs for everything. The radius arm frame bracket bolts were coated with thread locker and torqued to 100 ft-lb per specs.
Once the new brackets were installed, the long-travel radius arms were bolted into place. The new arms came with urethane bushings.
The lift kit includes a drop-forged pitman arm to keep the steering geometry within stock parameters.
We had to cut the bottom corner off the factory dual-shock brackets to clear the new radius arms where they wrap around the axle beams. This isn’t necessary on F-150s and Broncos with single front shocks.
Both brackets that attached the I-beams to the crossmember under the oil pan had to be removed, which required grinding off a dozen rivet heads in very tight confines. This was the most time consuming part of the installation. After the rivet heads were ground smooth, they could be punched out. Arrows show the locations of the rivets.
Once the old brackets were removed, the new drop brackets were bolted into place and the axles remounted into their new location.
Note: Pro Comp’s 4-inch lift kit uses the same drop brackets for their 6-inch kit. The upper axle beam mounting hole is for the 4-inch lift, the lower is for the 6-inch. (This is a good time to replace the axle beam bushings too.)
After the drop brackets and axle beams were bolted in Blanchard slid in the new progressive-rate Pro Comp coils, attached the ES3300 shocks, and the longer braided brake lines.
We opted for Pro Comp’s replacement 4-inch leaf spring packs instead of an add-a-leaf or lift block in the rear. New rear springs ensure that the suspension is not suffering from sagging issues.
Richard McFarland, Dunks’ alignment specialist, adjusted the caster and camber after the lift was installed to make sure our Bronco tracked straight and true on-road and off. It was pretty close to being in factory specs before he made the adjustments, which attests to how well Pro Comp designed the kit.
The 4-inch Pro Comp long-travel Stage II suspension gave our Bronco plenty of wheel travel and no clearance issues running 33-inch LT305/70R16 Pro Comp A/T Sport tires. The offset of the 16x8 Pro Comp Extreme wheels did require a 1-inch spacer.

Trail Report: Pro Comp A/T Sport

Pro Comp’s A/T Sport is a load-range E pickup/SUV tire with a 60,000-mile treadwear warranty. It’s designed for those who use their 4x4s as daily drivers and for weekend forays into the backcountry.

The Pro Comp A/T Sport, which is the tire we chose to run on our Bronco, has a tread compound that is engineered to work across a wide spectrum of driving conditions. The grooves and siping are ideal for expelling water so the rubber stays in contact with wet road surfaces, while the more aggressive, staggered side lugs improve traction over rocks and softer terrain. The A/T Sport also uses alternating tread block sizes to help reduce tire-generated noise.

We have only put a few hundred miles on our LT305/70R16s as of this writing. Our initial impression is they are one of the quieter A/Ts on the market, and the grip on pavement and over rocky, sandy terrain is impressive. The highway ride is a little firm as one would expect from a load range E. But drop the air down for medium-type summer trail running and they seem to do well against chipping and cuts. The 60,000-mile treadwear warranty gives us confidence they will remain for a number of years to come. We’ll have a full review of the Pro Comp A/T Sport soon.


Pro Comp USA
Compton, CA 90220
Dunks Performance

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