Barn Find Dentside Restoration: Gears, Lockers, Disc Brake Conversion, and More!

From day one, our barn find Dentside restoration project was slated to be an adventure vehicle. We wanted our Ford F-100 to be a well-equipped overland truck that would have low gearing, big brakes, and locking differentials at both ends. This would be the bare minimum we would accept. Current upgrades include 35-inch tires, and 4 inches of lift. Let's talk about how and why we picked the parts and gearingfor the dentside.

Understanding the Forces at Work

The stock gearing on our Ford F-100 barn find dentside restoration project was designed to get good fuel mileage (among other things) with the stock tires. As the vehicle tire size increases, the fuel mileage may decline, and the added leverage can begin to strain the drivetrain. So, do we try to match the original final drive with the new tire size, or do we go to a lower gear than that?

With larger tires comes more lift to create tire clearance. All that wind under the vehicle and across the top of a large, aggressively-treaded tire at speed causes more wind resistance. This is the reason newer vehicles are so low to the ground, with small wheel openings. To overcome this additional wind resistance, we need more leverage in the form of a lower gear ratio. Wind is not the only new force applied to the drivetrain, though; we need to factor in the rotating mass of the tire. As the tire increases in weight, it creates a flywheel effect that the vehicle needs to overcome during accelerating or decelerating (starting or stopping rotation).

Other factors that affect axle ratios are the transmission gearing, transfer case gearing, and optimum engine rpm in the working range.

The Right Gearing for the F-100

We know our barn find Dentside restoration project is not very aerodynamic, so we chose to go with a gear ratio that was lower than the factory final drive. Tires with a diameter of 35 inches are commonly paired with a 4.56:1 gear ratio. This helps get that rotating mass turning from a stop and maintains a solid working rpm of 2,200 @ 71 mph when paired with a 0.70 overdrive of a newer transmission. Since we have had a great experience with Motive Gear in previous builds, we installed PN D44-456 gears in the front axle and PN F890457 gears in the rear axle. The Performance Differential ring-and-pinion from Motive are made in Italy. The install kit had Koyo Bearings from Japan. All the parts had a premium feel coming out of the box.

Refresh

There is an unwritten rule that if you take a part off of a vehicle to work on it, you must clean and paint it. Since it's so much nicer to work with all new parts, we decided to pull both axlehousings and have them sandblasted and powdercoated. The rear housing would also get a drain plug added for easier maintenance intervals.

Front Axle

With the ring-and-pinions chosen, we needed new carriers for the lower gear ratios. The ARB Air Locker has a proven track record, so that got the nod. The front axle in the F-100 is an open-knuckle, high-pinion Dana 44 housing. Up until the Jeep Wrangler JK and JL came out, this was one of the best 1/2-ton front housings you could get from the automotive world, and it is still pretty tough even by today's standards. The shortcoming of using this housing was the axle U-joint size. The 760 U-joint was much smaller compared to the U-joints in a new Rubicon JL axle.

FOLLOW THE ENTIRE F-100 PROJECT:

• Barn Find Dentside Restoration Part 1: Road Trip!
• Barn Find Dentside Restoration Part 2: Suspension, Wheels, Tires, and More!
• Barn Find Dentside Restoration Part 3: Stolen, Recovered—and Reimagined!

In order to remedy the weak factory axleshafts, we got a set of Ten Factory chromoly axleshafts as a complete set (PN 22175). The axleshafts came out of the box factory-assembled with a black oxide finish and were ready to install. We used the RD116 ARB Air Locker and sealed it up with an ARB cast diff cover (PN ARB750003). This additional armor will keep the oil inside the diff when the rocks attack. Examine the diff cover shape closely and you will notice that it is designed to retain case pressure on the differential setup. Some axlehousings will flex under the strains of extreme use, so any additional strength added to the housing will help keep the case preload in the target specifications.

Rear Axle

The F-100 came with a Ford 9-inch rear axle. The only parts we recycled were the housing and brake backing plates. We used ARB Air Locker RD999, and this carrier was designed for 35-spline axles. Upgrading to 35-spline axles requires larger carrier bearings, which meant we would need to get a new case with a 3.25-inch bearing journal. Having a few race car guys around the shop helped us find a good usable case to start the install. The custom 35-spline axleshafts came from Strange Engineering. The 'shafts were forged out of 1550 premium steel with a Rockwell hardness of 60. This proven recipe is known to withstand 1,200-plus horsepower. Strange Engineering specializes in racing applications and the high-quality axle blanks are pre-machined, so all the company needs to do is put the customer's final touches on. This helps turn the parts around fast for quick delivery.

Air Supply

Very few onboard air compressors measure up to the CKMTA12 ARB High Performance Twin on-board compressor. We've used this compressor on multiple builds and put it through the toughest conditions, and it flat performs. We like to mount the compressor high in the engine compartment and away from heat if we can. In this case, we found the inner fender near the battery made a great location and it was easy to route the wiring. The compressor comes with a paper template to mark and drill holes, so mounting was straightforward. ARB has some of the most robust wiring looms, but we needed to shorten the loom instead of just coiling up a bunch of extra wire in the engine compartment.

We chose to neatly unpin the main connector and shorten the wires at the connector, and we used Delphi Metri-Pack 280 series pins in 10-12 gauge that we ordered from Amazon. On the business end of the wiring loom, ARB leaves the terminal connection up to the installer. We chose to use copper battery lugs soldered in place for a clean connection, followed by some heatshrink with glue built in to help keep moisture out. Keep in mind that the CKMTA12 uses 70-plus amps when running, so all connections must be up to the task. The last wiring modification relates to locker operation.

The default ARB wiring makes sure the compressor is on before the rear locker will operate. The front locker is only available to use once the rear locker is engaged. This is by design, to save the front axles from abuse; in our world, we often want only the front locker to assist in a tight turn where backing up would put you off the line. So, we simply connected the red wire on "switch one" to the yellow wire location on "switch two" with a jumper wire making switch one and two operational any time the compressor is armed.

Stop It!

Drum brakes were standard on '73-'75 4WD F-100s. The vehicle stops well with small tires and no payload, but front drum brakes have a nasty habit of fading fast, hating water worse than cats do, and becoming unreliable when out of adjustment. It was time to upgrade our F-100 to disc brakes. Many articles have been written on how to hunt wrecking-yard disc brakes from later-model vehicles, but in many cases these older rigs in the wrecking yards have been picked clean and crushed. So, we opted to use a complete kit from Jeff's Bronco Graveyard. This comes with all new parts, and everything to install 11-inch single-piston disc brakes on the old drum-brake spindles.

Nowhere on the Bronco Graveyard website did it say this kit would fit on a F-100, but Ford did a great job sharing parts across multiple platforms. The disc brake installation instructions were very light. One must have decent skills and understand vintage Dana 44 axles before committing to an install like this. While the races were factory-installed in the hubs, the rotors and studs needed to be pressed together. The factory Ford knuckles had to be clearanced so the Chevy calipers could travel uninterrupted during braking. Everything went together well, and the quality of the parts was premium. They only lacked some sort of coating on the cast-iron parts.

We chose to use a high-heat paint to help slow down the rust. While the front axle got new disc brakes, we retained the rear axle's 11-inch drum brakes. Why is that? Well, 70 percent of your vehicle's stopping ability comes from the front brakes. The rear brakes support role is small, but when it comes to the E-brake, we want the biggest we can get to hold the F-100 in place on the trail. From the backing plates out, we replaced all the rear brake components with new.

Hydraulics

The factory drum-brake lines from the front axle would no longer support the new disc brake kit, so we created new stainless-steel lines designed to stay out of harm's way when the trail gets nasty. In the rear we used the same stainless-steel lines to replace the rusty, frozen OE equipment.

Tires and Wheels (Round 2)

As you recall from part three, after being stolen the F-100 was returned to us without wheels and tires. Milestar Tires and 4Wheel Parts got wind of what happened and decided that we could use a little help on another wheel and tire package. This was incredibly generous and humbling. The off-road industry truly bands together like family.

Read on for the fine details of the modifications and brake, wheel, and tire upgrades we made to our dentside project.

A little more room was needed for the caliper to travel under braking.

The rubber front brake hose is actually a rear-brake application hose. Using redundant parts helps to decrease the spare parts we need to carry.

The 11-inch drum brakes received all new components.

The stainless brake lines were fun to build, so we also made an extension for the diff vent.

All these parts were discarded simply because we wanted 35-spline axleshafts.

The 35 spline axleshafts dwarf the 31-spline stock units.

Notice the new axle has a smaller mounting flange. This decreases rotating mass.

The Ford 9-inch appears stock but has a larger bearing diameter to accommodate the 35-spline axleshafts.

The ARB Air Locker assembly was installed into the high-pinion Dana 44 without a hitch.

This hole in the Ford 9-inch will soon be a threaded drain. The Ford 9-inch has no drain, so we added a weld-on bung to make oil changes easier.

The bung for the drain plug will be welded inside and out.

Onboard air is a must for anything with pneumatic lockers. Airing up tires is a perk. We chose a CKMTA12 ARB High Performance Twin on-board compressor to provide air pressure.

Here's a look at the ARB Air Locker's switch wire loom before we modified its length.

With the Delphi Metri-Pack 280 series connectors, we shortened the wire loom for a form-fitting install.

We soldered copper lugs in place for a solid connection to power for the ARB air compressor.

Here's how the ARB compressor looks mounted to the fenderwell of our F-100.

Both Milestar and 4Wheel Parts stepped up and sent us wheels and tires to replace the stolen set. The wheels are 8.5-inch-wide 4Wheel Parts Factory T-Series wheels with 4.75 inches of backspacing so the tires will clear the fenders at full bump. The Patagonia X/T tires measure 35x12.50R17LT and fill the wheelwells perfectly.

4x4 Garage Video Series! Episode 1: Updating A 1988 Ford Bronco Suspension

In episode 1 of the new video series 4x4 Garage, host Christian Hazel tears down the suspension of a 1988 Ford Bronco for a 6-inch Superlift system and dives into the axles to prep them for new 4.88 gears and Eaton TrueTrac differentials to support the 37x12.50R17 Falken A/T3W all-terrain tires for awesome performance. Want to see more? Subscribe to the MotorTrend YouTube channel!