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Swapping A 10-Bolt For A 9-Inch While Retaining GM SuspensionTen To Nine From the June, 2012 issue of Rod & Custom By Kev Elliott
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Ever since I first put my roadster pickup together some 12 years ago I’ve always been aware that the rearend was the weak link. I had the TH350 rebuilt, and the small-block was fresh, but the 10-bolt was straight out of a junker ’82 Caprice, complete with the stock triangulated four-link. The axle bearings run directly on the driveshafts on these axles, and mine always leaked, even after the fitment of “axle-saver” bearings a few years ago. When I had the bed off to prep it for paint, I figured the time had come to swap the axle for a better version. I acquired a 1-inch narrower 10-bolt from a later model wagon and intended to swap my brackets over, but ultimately opted to install a Currie Enterprises 9-inch Ford-based rearend and fit my GM brackets to that, especially after I found that Currie manufactures adjustable tubular arms exactly for my application. A no-brainer, right? When I first built the truck... When I first built the truck 12 years ago, I used the 10-bolt rearend that came from the same ’82 Caprice that donated its front clip. I even used the stock antiroll bar, shocks, and pressed-steel triangulated four-link. While I was swapping the rearend, I also figured I’d replace the MGB coil springs I’d used. Always a little on the stiff side, I figured it was a truck and didn’t worry about it, until I loaded the bed with several bags of concrete, and suddenly found the suspension worked and the truck rode way nicer! So, I needed softer springs. Rather than the existing separate shocks and springs, I opted for coilovers, and spoke with the folks at QA1 about my project. I’d measured and knew the extended length of coilover I could fit, and weighed the rear of the truck to determine the spring rate. Though the QA1 catalog lists a chart to calculate the spring rate based on vehicle weight, and another for the corrected rate of coilover springs that are mounted at an angle, the company’s tech guy I spoke to on the phone was extremely helpful and we had it worked out in a few minutes, and the coilovers were on their way! It worked out like this: The rear of the truck weighed just over 1,700 pounds, for which QA1 recommend 225-pound springs. As ours would mount at 20 degrees, the rate needed to be higher. Using the QA1 chart it worked out to 225 ÷ 0.88 = 255.68, so we selected 250-pound springs. The QA1 Proma Star coilovers we selected are single adjustable with 18 valving options. Though they’re available with bearings, we opted for poly bushings top and bottom, as the truck is more a long distance driver than an autocross assailant, and the softer bushings offer a more comfortable ride! With modified lower and custom-made... With modified lower and custom-made upper mounts, MGB sporty car front coils have supported the rearend all this time, though admittedly were a little stiff with an unladen bed. Actually, the coilovers are mounted at less than 20 degrees, but until I had the new axle in place I wasn’t sure of the exact angle, so I erred on the side of caution. While I originally planned to mount them vertically behind the axle in a similar location to the old coils, I was pretty sure I’d be able to use the original lower shock mounts in front of the axle. However, I wasn’t sure on clearance between the spring or upper spring cup and the chassis. As it turned out, all was good, so I strengthened the lower shock mount to take a coilover, and modified commercially available brackets for the upper mounts. I’d had Currie leave the shock mount section of the original brackets un-welded so I could remove them if they weren’t used, so I just had to weld them to the housing to finish the installation. All in all, a relatively easy conversion with only minimal fab work to complete. The truck now rides way better, and I have adjustable compression/rebound, as well as adjustable pinion angle should I need it.  Currie Enterprises carries...  Currie Enterprises carries a number of axle brackets in stock, but not for my application, so I asked them to retain the lower shock mount when they cut them off, which were integral to the lower suspension arm bracket.  With new tubes cut to length,...  With new tubes cut to length, new Torino big-bearing ends, and a new centersection, there’s not a Ford part on a new 9-inch from Currie. With the housing tack-welded together in this fixture, it’s checked for the desired length.  Currie keeps a number of old...  Currie keeps a number of old rearends in stock to check the location of brackets or to measure widths. Our rearend is in the rotating jig in the background, which ensures a decent weld around each end of both axle tubes, as well as allowing it to be positioned for ease of welding on any brackets.  Once shot-blasted, our less...  Once shot-blasted, our less than perfect GM brackets were offered up to the new housing. Held in place with a magnet, this neat little level is placed on a bolt to ensure the bushings in the four-link will be parallel with the housing.  Again, a number of jigs like...  Again, a number of jigs like this one ensure the upper Johnny Joint brackets are mounted in the correct position, depending on application.  With the housing and brackets...  With the housing and brackets fully welded, the assembly is placed in this fixture to be straightened. A dummy centersection is bolted in place, and a round bar passed through fixtures where the bearings would be. With pressure applied by a hydraulic ram, when a similar fixture on the bar fits in the bearing housings at the axle ends, it’s straight.  Seeing as we showed Editor...  Seeing as we showed Editor Rob’s third member being assembled recently, we’ll skip the next few steps, but here are all the components that are required. I chose 2.80 gears, which is close to what had been in the 10-bolt. Not exactly quick off the line, the 22 mpg they returned more than compensated for this! For a more in-depth buildup of a Currie axle and third member, check out the tech section at www.rodandcustommagazine.com.  Gear marking compound is applied...  Gear marking compound is applied to the ring gear to establish the contact pattern between it and the pinion gear during assembly. Ours required the pinion be removed and another shim added to achieve this pattern.  While our third member was...  While our third member was being assembled, at the other end of Currie’s facility, our axle shafts were getting the splines cut.  With the housing shot-blasted...  With the housing shot-blasted and hot-tanked, it’s delivered to the assembly area along with the shafts.  Prior to assembly, a rotary...  Prior to assembly, a rotary brush cleans the inside of the axle tubes.  This magnet is placed inside...  This magnet is placed inside the pumpkin while the housing is cleaned. Note how much shot from the blasting process is collected, even after hot tanking.  This fixture checks that the...  This fixture checks that the axles are the correct length for the housing prior to final assembly.  This tool is used to install...  This tool is used to install the Currie-designed Johnny Joints, after they’re lubed and ready for assembly.  With the seals installed in...  With the seals installed in the housing ends, a bead of RTV sealer is applied to the housing, then a gasket and another bead of sealer before the third member is installed.  Once the wheel studs are pressed...  Once the wheel studs are pressed into the axles the retainers are installed and the bearings pressed into place.  Finally, the brake drum backing...  Finally, the brake drum backing plates are hung on their studs and the axles are installed before everything is bolted in place.  The new and the old. Not only...  The new and the old. Not only is the 9-inch stronger but it eliminates the C-clips that retain the GM axles in place. Currie Enterprises supplies their own brand of gear oil.  Prior to removing the old...  Prior to removing the old rearend, we weighed the rear of the pickup (and added the weight of the bed) to determine the spring rates we’d need for coilover shocks. See the main text for how we calculated our required spring rate.  We selected a pair of QA1...  We selected a pair of QA1 Proma Star coilovers, with an extended height of 14 inches and compressed height of 10 1/8 inches, as the best option for our application after measuring the available space under the pickup bed floor. These are single adjustable for simultaneous compression and rebound tuning, with 18 valving options. We also opted for the thrust bearing kit for ease of ride height adjustment and a pair of spanner wrenches.  The thrust bearings are installed...  The thrust bearings are installed first, both washers coated with antiseize lubricant (not shown). They fit from above, as the adjuster knob doesn’t allow fitment from below.  When we discussed our project...  When we discussed our project with the guys at QA1, we were warned our springs would require compressing slightly for installation, though most do not. With the springs compressed, the upper spring cap simply slid into place.  It’s probably not common knowledge...  It’s probably not common knowledge that Currie Enterprises manufactures adjustable suspension arms for GM A-body applications. As our pickup used stock A-body pressed-steel arms, this was a direct bolt-in swap. Even the antiroll bar bolts through the lower arms! We simply set the new arms to the same length as the originals and bolted them in. These new arms are infinitely stronger than the flimsy stockers, and have greatly improved the ride.  Though we’d asked Currie to...  Though we’d asked Currie to leave the lower shock mounts in place on the lower suspension arm brackets, we also asked them not to weld that part of the bracket to the housing, as we weren’t 100 percent sure we were going to use them or whether we’d mount the coilovers vertically outside the framerails.  With the new axle in place,...  With the new axle in place, however, the neatest option was obviously going to be to use the stock lower brackets. They were designed for shock absorbers though, not coilovers, so the marked section was removed with a plasma cutter and the steel bung shown welded in place to offer more support for the lower coilover bolt.  We also added a tab to the...  We also added a tab to the mount so the coilover wasn’t mounted in single shear, after checking for clearance against the lower suspension arm. The bracket was welded to the housing now as well.  While we’re sure there’s a...  While we’re sure there’s a scientific way to calculate how much a coilover will compress, we’ve always raised the chassis 1 inch from its ride height relationship with the axle, and installed the upper mounts with the coilover fully extended. This allows for compression under the weight of the car, and they are adjustable after all! The coilover was protected with a fire blanket during tack welding, and then removed for final welding.  Finish welded and with the...  Finish welded and with the truck back on its wheels, it sat at exactly the same height it had before we swapped the rearends—only now we have adjustable ride height and pinion angle as well as adjustable suspension quality, depending on use or even weight in the bed.  With the exception of bolting...  With the exception of bolting the antiroll bar in place, and fabbing new brake hard lines, the install is complete. Currie supplied a pinion yoke that matched the length of the old GM one, meaning we could reuse the same driveshaft.
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