14-Bolt Disc Brake ConversionPosted in How To: Transmission Drivetrain on March 1, 2011 Comment (0)
The GM Corporate 14-bolt rear axle is considered one of the best options for the ultimate in high strength for a trail/street machine. Found in four different variations from 1973 to 1996, the GM-based rearend packs a serious arsenal of wheeler-friendly attributes, some of which include a third pinion support; a removable front pinion support; built-in carrier preload adjusters; a full-floating design which relieves the (stock) 30-spline axleshafts of weight-carrying duties and hence increases torsional strength; and a massive 10.5-inch ring gear. These axles are easy to find in wrecking yards across the country and will typically cost you somewhere in the neighborhood of $300 to $500 depending on condition. All 14-bolt axles feature a uniquely shaped differential cover that employs 14 bolts to secure the cover to the centersection-hence the name.
Another commonality of the (pre-1988) 14-bolt is drum brakes. Unlike disc brakes, drum setups hold heat inside a contained drum assembly. With little or no air flowing over critical areas where friction occurs, drum brakes fade quickly, significantly reducing net stopping power. Unfortunately, enthusiasts still rely on the 14-bolt's antiquated drum brake technology today. Despite the fact that these brakes were never intended to handle the added leverage of plus-size tires, we see them on the trail all the time. While drum brakes will slow a vehicle down, you simply cannot expect the same performance as you would from discs. The reason for this is that 70 percent of a vehicle's braking force occurs at the front end. This is why all vehicles built since the mid-'70s employ disc brakes up front. The reason most pickups and SUVs came with rear drum brake arrangements (into the late '90s) was largely due to the higher cost of manufacturing associated with disc brake setups. Over the years, as vehicles have become lighter to achieve higher fuel economy standards, manufacturers have phased out the portly drum brake setups in favor of lighter disc arrangements. As such, brake performance has increased. However, so has the cost to manufacture a typical rear axle-a cost that is generally passed on to the consumer. This leaves the budget-minded truck builder in a tough spot where sacrificing stopping power is the only realistic option.
To combat this problem, the folks at Off Road Design (ORD) developed a bolt-on 14-bolt disc brake conversion kit that will not break the bank. ORD does not claim that this setup will improve braking performance in all conditions, but they do tell us that the setup will perform more consistently for trail environments where outside elements such a water and mud can diminish stopping power greatly on drum brakes. The system is easy to install and typically costs less than rebuilding the factory drum arrangement. By design, the discs shed heat more effectively, thanks to their exposed surfaces. They also take advantage of centrifugal forces and are able to shed water and mud more quickly than drums- so there are fewer ill effects on brake performance. All things considered, it's a win-win scenario for the 14-bolt owner. Check out the highlights from the conversion process.
Other Things To Consider
This conversion does not include a mechanical parking brake option, so another type of parking brake is recommended. This could be a line-lock or a transfer case-mounted parking brake setup. ORD is currently developing a line-lock kit to complement this conversion, but was unable to provide us a release date at the time of print. Some vehicles may need an adjustable proportioning valve to properly supply enough brake fluid volume and pressure to the rear disc brake calipers. Some vehicles work just fine with the factory setup, but you will not know until you actually test it. Factors that can affect brake bias include wheelbase length, center-of-gravity height, overall weight, axle type, driving style and terrain. The proper brake setup really varies from one rig to the next, so you may need to experiment a little to get the desired braking levels. It is also possible to adjust the front-rear brake bias by selecting a different caliper size. There is a heavy-duty brake option on the 3/4-ton pickups that used a larger piston caliper. ORD recommends running larger calipers up front and a smaller caliper in the back. Once these items have been addressed, the vehicle should exhibit improved braking performance. If something does not seem right, you may need to upgrade to a 3/4- or 1-ton master cylinder, but know that the 1-ton system requires switching to hydroboost.
ORD offers optional 16-inch braided stainless brake lines for $65 at the time of print. Keep in mind that the customer must specify either a 10mm or 7/16-inch banjo bolt. Also available is a "long line," as shown here. Both kits use Kevlar/stainless braided lines.