Factory Heavy-Duty six-lug
It had only been two weeks since we'd installed an Auburn ECTED in a 10-bolt axle up north ("Auburn's ECTED," Aug. '06), when we blew out the same style axle in our daily-driver Tahoe here at the office. It was right at its classic breaking point of 95,000 miles.
We know we've abused that poor 10-bolt, but that doesn't mean we have to like that it is a weak axle.
We had a solution that we've been waiting to try but never had the chance. In the late '80s and into the '90s, GM had some light-duty six-lug 3/4-ton trucks, and it wasn't just some beefed up 10-bolt that they came with. It was a semifloating 9.5-inch ring-geared, a scaled down version of the standard 14-bolt axle, with a 6x5.5 lug pattern.
Think that's sweet?
Want to know what's even sweeter? All it takes to fit it are one conversion U-joint and a set of U-bolts. We found a semifloating six-lug 14-bolt in really good condition for around $500 at our local parts yard. Even the brake lines weren't squished. What a score!
We heard a little noise from the rear end, and then nothing. What do you think could have happened?
We'd heard how this 9.5-inch ring gear 14-bolt was a drop-in swap. The spring pads lined up, and the width of the axle was within an inch of our original 10-bolt. But we wanted to make sure that the length of the new centersection (from the axleshaft centerline to the tip of the yoke) was close enough to our old 10-bolt's length. Sure enough, the 10-bolt was only half an inch shorter, therefore not requiring us to make any driveshaft modifications. And as for getting the R3 U-joint driveshaft to mate to a 1350 U-joint yoke? No problem, that exact conversion U-joint is readily available (Precision U-Joints, PN 447).
Remember that you're never supposed to reuse U-bolts. Now with that said and out of the way, we were busy grinding our old U-bolt plates to accommodate the larger circumference of the semifloating 14-bolt's axletubes. And since we couldn't find new U-bolts during our after-hours project, we snapped it back together with the old ones temporarily so we could at least get home.
It's not just a six-lug pattern that you get with a bigger ring gear and axleshafts. It's also this much bigger drum brake on each side that makes the drop-in 9.5-inch ring gear 14-bolt so sweet.
Almost everything bolted back into the same location without any modification. Our new axle did not have sway-bar mounts on it (1/2-ton and 3/4-ton trucks typically do not have rear sway bars, but Tahoes and Suburbans do). Not having the sway bar actually improved the ride of the rear suspension a little, but the rear tosses out in corners more easily. New perches can be added easily enough to the 14-bolt to accommodate a sway bar.
One issue we had we caused ourselves, so please learn from our mistake. Since the new axle's emergency brake cables were in great condition, we simply cut our old 10-bolt's off since they were giving us a little grief. We weren't going to use them again, right? Wrong! The semifloating 14-bolt axle is out of a truck with a different frame and the brake cables are longer. So now we need to replace those perfectly good brake cables that we cut to save ourselves five minutes. Remember to reuse the original emergency brake cables.