Swapping In 3/4-Ton Axles

One of the drawbacks of a full-floating rear axle is that the drum brakes are challenging to service. You must remove the axleshafts and two interlocking hub nuts just to pull the drums. To avoid this and increase the braking power of the truck, this GMC was fitted with an ORU disc-brake kit. The original hubs were used for this swap so the lugs were driven out and the hub and drum separated.

Detroit Locker from Reider Racing was used in the 14-bolt. The unit for this rearend is a little different than other Detroits. The locker (lower left) functions exactly the same as a Detroit for other applications, but it replaces only the two side gears and four pinion gears inside the original carrier. For most other axles, Detroits replace the whole carrier.

Another gear-installation kit from Reider Racing was used by Valencia to set up the 14-bolt and check all vital statistics. In addition to the parts provided in these kits, ORU installed new inner and outer axle bearings and seals to complete the rebuild on the front and rear axles.

The original shocks bolted right up to the mounts on the new rearend. Because the 14-bolt is heavier, however, there will be more axle droop and you should check for adequate shock length. The mounts on this rearend were tweaked pretty badly, so Valencia cut and replaced them with custom brackets that ORU offers.

Mauricio Natera installed all of the disc-brake parts on the 14-bolt, including a custom spacer (shown), new backing plates, rotors, and calipers. The rotors are the same diameter as the front, and the calipers are GM units. Valencia installed Pro Comp braided-steel brake lines from the calipers to custom-bent hardline mounted on the axlehousing.

Aluminum ORU diff covers were used front and rear. They add fluid capacity to the axles and dissipate heat more quickly than steel. They also look a heck of a lot better. There was some question about their durability on tough rockcrawling trails, which is addressed in our "So What?" sidebar.

The brakes were finished front and rear with a Pro Comp braided-steel line kit. These hoses are extra long to allow for plenty of axle movement and are DOT legal. The 3/4-ton swap didn't require any special lines because the 1/2-ton calipers were retained up front, and Valencia bent new hardlines for the rear and used the junction block off the 12-bolt.

The final step in an axle upgrade is to connect them to your 1/2-ton truck's transfer case. One route is to have your original rear driveshaft shortened and have the axle end replaced with one that holds a 1350 U-joint (the 1/2-ton rear used a 1310).

The 1350 U-joint is larger and stronger, and the best option is to have an all-new driveshaft made. This one is from Denny's Driveshaft Service, and it features sealed U-joints and an extra-long slip joint. Denny's also provided a new output for the NP205 that accepts a 1350 U-joint.