Step By StepView Photo Gallery
Removal of the 12-bolt axle began by dumping the clutch on a freshly swapped-in 383 with aluminum heads. Instead of smoking the 35-inch tires, an axleshaft snapped and pieces of spider gear spit out through the differential cover. What was left of the housing was junked after the U-bolts, driveshaft, and brake lines were removed.
New 3-inch axletubes are pressed into a 10 1/2-inch ring gear 14-bolt differential housing to convert this axle to a semifloating design. Sealed bearings are then pressed on to 1.53-inch, 30-spline, semifloating axleshafts with a 6-on-5 1/2-inch bolt pattern. These axles are available in three different widths to fit 73-87, 88-98, and 99-and-newer GM trucks.
The spring perches must be welded to the housing in the proper location, so the axle was mocked up with larger-radius U-bolts and new lift blocks. The original lift blocks were too tall when used with the new axle because the axletubes are bigger on the 14-bolt than on the 12-bolt.
Two plumb lines were dropped from the framerails to serve as a reference point for all measurements. The axle was centered in relation to the chassis, and the U-bolts fastened before lowering the truck back to the ground. With the truck on the ground the suspension was cycled a few times and the pinion angle was set at 2 degrees lower (towards the ground) than that of the yoke on the transfer case.
The spring perches and shock mounts were welded onto the axle after all measurements were verified. Stock drum brakes were used in this application so new brake lines were made and connected to the factory system. The parking brakes are also the same so they reattached like the 12-bolt stuff. A new rear driveshaft will be required with this swap because the pinion length and U-joint size are different on the big 14-bolt.
People will do a double take when they see your new 1-ton axle spinning your six-lug wheels. ORU wanted to upgrade this axle and install one of its polished aluminum differential covers, but because of the gas tank placement on this 70 Blazer, there were clearance problems. The stock cover will fit without any problems.
We know you have drooled over these huge 10½-inch, full-floating Corporate 14-bolt axles before. Youve seen them in ¾- and 1-ton GM trucks powered by 454s or diesel engines, and you have dreamed of the day when you will swap one of them into your truck. And why not? Detroit Lockers for these axles sell for around $300, most have 4.10 gears already, and your buddies swear that theyre unbreakable. Sure, it will scrape the earth like a plow blade, but we joke around the office about bolting a caster wheel on the bottom of the housing to solve that problem.
The beauty of GM products is that this axle will nearly bolt right into any of its light trucks with a driveshaft modification. Too bad these monsters only came as eight-lug deals with those huge full-floating hubs. Up until now you have had to run eight-lug wheels to take advantage of GMs strongest axle. That may not be a problem for youunless you already maxed out the credit card on the six-lug wheels of your dreams. Or maybe you are IFS equipped and there is no easy way to upgrade the late-model ½-ton front to eight-lug hubs. For someone like you the ideal solution for ultimate strength would come in the form of a 10½-inch 14-bolt with six-lug axles. So here it is.
Off Road Unlimited has been building trucks with big-block power for years, and it understands wheelers needs. ORU now offers a hybrid six-lug 14-bolt axle thats complete drum-to-drum with Superior Axle gears, shafts, and a Detroit Locker for $2,995. It will hold up to all the power you can make, and there is no need to buy new wheels. Just slip this Franken 14-bolt in place, weld on your shock mounts and spring perches, and have a new driveshaft made to tie it all together. ORU let us follow along as its guys swapped this new 14-bolt into a four-speedequipped K5 Blazer that had retired its last 12-bolt.