To have the stock rear axles...
To have the stock rear axles and brake drums redrilled to match the new bolt pattern of the front disc brakes, I took my Stepside to Brian Elbert at B&D Fabrications. Brian does this kind of work, along with other rearend repair and modification, everyday, but the process still takes about 5 hours to complete.
If you are going to the trouble of upgrading the brakes on your C10, you are more than likely going to want to have matching wheels on the front and rear of the truck. Since the upgrade to the front from stock drum brakes to disc brakes in the accompanying article changed the bolt pattern from six lugs to five lugs (5-on-5 bolt circle), it's necessary to address the rear axles in order to have matching wheels. You have a couple of options in how to go about doing this. To keep your existing rear axle housing, you can change the bolt pattern by replacing the axles (and brake drums) with new ones in the bolt pattern you need or you can have the axles and brake drums redrilled. If you choose to have the axles redrilled, you should install new wheel studs, rather than reusing the old wheel studs.
In either case, you will be required to remove the axles from the housing. To do this with a typical GM truck rearend, jack up the truck and secure it safely on jack stands if you are not using a garage lift. Put the transmission in neutral, as you will need to be able to rotate the gears in the differential. Place a drain pan under the rearend cover and then loosen the cover bolts enough so that the gear lube drains out of the rearend. While the gear lube is draining, remove both rear wheels. When the gear lube has drained out of the differential, completely remove the bolts securing the cover and set the rearend cover aside (letting it soak in a parts cleaner would be a great idea). Now remove the cross-shaft retaining bolt and then pull the cross-shaft outward. The cross-shaft does not need to be removed completely, just enough so that the axles can be pushed inward. When the axles are pushed inward, the axleshaft C-clips should fall right out. The axles can now be pulled out. After pulling the axles out of the housing, inspect them for wear or other damage.
While the truck was up on...
While the truck was up on the lift, it was a good time to take a closer look at the underside of my relatively new project. The trailing arms look to be in satisfactory condition. While the brake line is bent and routed vey sloppily, it does work. Most likely it will be replaced eventually, especially if the stock rear drum brakes are upgraded to discs. The lower shock mount "adapter" bracket really should be eliminated. Setting the truck to the desired ride height and then replacing the shocks with those of the appropriate length would have been a better fix than installing this mounting plate.
The first step is to remove...
The first step is to remove the rear cover and drain the gear oil to gain access to the cross-shaft retaining bolt and cross-shaft.
Before the axles can be removed,...
Before the axles can be removed, the wheels and tires must be removed. Then the brake drums will need to be removed so the axle can be pushed inward.
The cross-shaft retaining...
The cross-shaft retaining bolt must be removed and then the cross-shaft (round bar stock parallel to the ring gear) is pulled outward enough so that the axles can be pushed inward. When the axles are pushed inward, the C-clips that retain the axles within the housing will fall out, allowing the axles to be removed.
If you choose to replace the axles, you will first need to determine the axle diameter, axle length, and number of splines, and then find suitable replacements that have the desired bolt pattern. Unless you are able to purchase new axles that meet your specifications, you will need to verify that any candidates for replacements are not bent or otherwise damaged in any way that would make them unusable or short-lived.
If you have access to a machine shop that routinely redrills axles and brake drums, this is perhaps your best bet, as you already know that the axles are the correct size and will work. For our '68 C10 project, we chose to forego the salvage yards looking for axles, and went straight to B&D Fabrications to have the axles redrilled. The intent was to have the brake drums redrilled as well, but there were already several holes in the existing brake drums, so those were replaced with new drums. After Brian Elbert at B&D Fabrications does his magic on the axles, they can be reinstalled.
The axles can be pulled out...
The axles can be pulled out with relative ease. Just avoid pulling them out partially and applying any force that may cause them to bend. After pulling the axles from the housing, check them for wear or damage, and repair or replace as necessary.
Brian uses a small grinder...
Brian uses a small grinder to remove the remnants of any previous gasket material from the rearend. All traces of the old gaskets must be removed for the new gasket to seal properly. With the gasket removed and the gear lube drained from the differential, Brian uses aerosol carburetor cleaner to aid in removing any gunk that may be within the housing. This also helps to clean the ring gear to check for signs of wear.
The stock axle is chucked...
The stock axle is chucked up into a metal lathe with the inner end of the axle centered in the headstock and the flange end centered in the tailstock. The steady rest is then positioned in the same location where the axlehousing bearings are.
While the large-diameter wheels...
While the large-diameter wheels that were on the truck had no interference problems, the new rally wheels would not fit over the brake register. The wheels were on hand, so they could be measured and the brake register sized accordingly. An extra step that Brian performs is to size the brake register to the correct size for the brake drums so that they are centered correctly. This is not a big difference, and may not even be necessary in some people's minds, but it is a little task that should help to reduce any rotational vibration that could present itself if not done.
After locating and drilling...
After locating and drilling the holes to 0.500 inch, they are reamed to 0.515 inch diameter.
When changing the bolt pattern...
When changing the bolt pattern from any five-bolt pattern to another five-bolt pattern, the holes could simply be offset equal distance from each other. However, changing from a six-bolt to a five-bolt pattern makes it a little more complicated. The discoloration around the bottom hole in the photo indicates where one of the existing holes was welded shut and then a new hole drilled in the same area. The walls of the original holes are slightly brown (rusty), while the newly drilled holes appear as fresh steel.
Brian recommends always replacing...
Brian recommends always replacing the oil seal anytime one is removed from the axle by using a pry bar. For the small price of the oil seal, it is simply not a place to cut corners.
After removing both axles from the axlehousing, Brian chucks up the axles in his metal lathe. While some people might not think about it, Brian knew that the brake register (hole in the middle of the wheel) of the GM rally wheels I planned to use would not fit over the hub end of the existing axleshaft. After measuring the wheel, he first turned down this end of the axle to the appropriate size. He also used fine emery cloth to lightly polish the portion of the axle that rides in the bearing located at each end of the rearend housing. Now it was time to locate the new holes for the wheel mounting studs. When going from one five-bolt pattern to another five-bolt pattern the process is pretty simple. However, since we're changing from six-lug to five-lug, it requires more steps. To ensure there were no weak spots caused by new holes being located too close to existing holes, he welded up one existing hole in each axle. This necessitates that the axles go back onto the lathe for a few cleanup passes to ensure no welding slag remains to interfere with the new mounting studs. With that completed, the new holes could be drilled. Brian feels that his drill fixture is proprietary to his business and asked that I not take photos or discuss that portion of the process. I respectfully obliged. For my specific vehicle, the holes are drilled to 1/2-inch diameter and then reamed to 0.515 inch. The wheels studs are then press fit at 0.530 inch.
A slide hammer is then used...
A slide hammer is then used to remove the bearings from the axle housing. While you don't always need to replace the bearings, it is not a bad idea. Since I have no plans to remove the axles for any additional modifications, it made perfectly good sense to replace the bearings now and be done with them.
The excess grease is wiped...
The excess grease is wiped away and then the new bearing is installed. Use of a bearing installation tool ensures the bearings go in properly.
The new oil seal is installed...
The new oil seal is installed and then the bearings packed with grease. Do not forget to grease the bearings!
Before installing the wheel...
Before installing the wheel studs, Brian uses a small grinder to remove any welding slag or burrs that may be left over from the filing or drilling process. With the axle supported by a vice, the wheel studs are installed by the Armstrong method and a Ford hammer.
Brian recommends replacing the bearings located at each end of the axlehousing and insists on replacing the oil seal whenever an axle is modified or replaced. The relative low cost of these two items makes this sensible when compared to the expense of having a damaged rearend repaired. Insert each rear axle, then slip a C-clip into the groove at the inner end of each axle, then slide each axle outward. Now push the cross-shaft into place and secure with the cross-shaft retaining bolt. Install a new cover gasket, reinstall the rearend cover, and secure with the bolts. Now refill the rearend with gear lube and reinstall the wheels and tires.
With the new disc brakes installed on the front and a matching five-lug bolt pattern front and back, the large-diameter, six-lug wheels that came with the truck must be replaced. Since my plans for this truck are more along the lines of a daily driver shop truck/parts chaser/magazine test mule, I plan to keep the expenses down and the reliability up by installing a simple set of GM rally wheels shod with some BFGoodrich T/A radial tires. I also have a fair amount of bodywork slated for this truck, so I don't want to install something flashy that will be covered with sanding dust and other bodywork grunge.
The original stock axles with...
The original stock axles with their new bolt pattern and new wheel studs are now ready to be reinstalled. Simply guide the axle into the bearing and then push it all the way into the axlehousing.
The wheel flange was painted...
The wheel flange was painted rattle can black before the studs were inserted to help deter the formation of rust on the freshly machined steel.
With both axles in place,...
With both axles in place, the C-clips, cross-shaft, and retaining bolt can then be installed.
The new, finned brake drums...
The new, finned brake drums are then installed. It may be necessary to adjust the brake slightly to get the brake drums to fit over the brake shoes.
The new wheels and tires can...
The new wheels and tires can now be installed and secured with appropriate lug nuts. Brian recommends checking the torque on the lug nuts after approximately 100 miles. Brian finishes the job by installing a new rearend gasket and then reinstalling the rearend cover. With the rearend cover in place, do not forget to refill the differential with rearend gear lube.