Building a 10-Bolt Rearend - Bolt ’N’ Go
From the August, 2011 issue of Chevy High Performance
By Sean Haggai
Photography by Sean Haggai
Proper road-going muscle cars these days have all their bases covered. They can go, turn, and even stop like our late-model favorites. These multipurpose sleds have obtained the appropriate stance through various suspension goodies, and extra grip and decreased stopping distances with wider rubber and an aftermarket brake system. They’re powered through stout mills and their transmissions are built, with the ability to take a direct hit from a tank shell. So what’s left?
If you’re paying attention, you’ve realized one vital component is missing from an all-purpose muscle car: a bulletproof rearend to take all the punishment. While your sled may have already come prepped with a posi unit from the factory, ours unfortunately did not. If you recall, our ’72 Nova began its life as a straight-six, which we quickly ditched for a supercharged small-block and a complete suspension and big-brake kit from CPP. We sent it right to work, too, and participated in nearly every autocross event we could enter.
We began by properly positioning...
We began by properly positioning the Nova’s rear subframe and rearend housing on jackstands. Then, we removed both rear tires and removed the lower QA1 shock bolt with an 11/16-inch wrench and 5/8-inch socket. We further disassembled the components by disconnecting the rear brake lines at the “T” above the differential cover with a 3/8-inch flare wrench. Then, we removed the four large nuts from the U-bolts, which fasten the lower spring perch to the underside of the leaf springs. Note: Check the condition of the brake lines for cracks or abnormal wear.
While ’72-75 Novas offered gear ratios from 2.73 to 3.42:1, both with and without posi units, most came with open differential 2.73 or 3.08:1. We got the latter with a set of lazy 3.08:1 gears in our 8.5-inch rear. Leaving stoplights was more of a chore, and exiting turns induced excessive wheelspin from only one tire. With this sort of limitation, remaining competitive was difficult. Besides, what’s the point of all that power with no means of laying it down?
Almost every component of the car can become a powerful tool, including the rearend. With power equally distributed at the rear tires, drivers can apply some extra throttle to induce the rear to kick out a bit, point the nose in the intended direction, and go. Plus, for drag-happy drivers, the benefit of having both tires receive traction is that they can produce better launches and quicker times. For us, this was a no-brainer and we researched Moser Engineering’s website to find everything we needed to revive our rearend. This included new 30-spine axles, a 3.73:1 ring-and-pinion, an Eaton posi unit, a performance cover, and even all the bearings, seals, and setup kit. We did all this and still salvaged our factory 10-bolt to house it all.
Before the rearend build could begin, we first had to get the factory member out of the Nova. From there, we stripped it down to its most basic form by removing the rear brakes, lines, and sway bar. Then, we sent it to the rearend experts at Manny’s Hardcore Performance (MHP) in Colton, California. All said and done, it took a couple of hours for the build, and we left with a serious piece of equipment for our Nova project.
The large bolt that secures...
The large bolt that secures the upper leaf-spring shackle to the rear subframe was also removed from both sides, using a 7/8- and 13/16-inch wrench. Once this was free, we gently lowered the rear leaves away from the rearend and dropped the housing onto a furniture dolly.
To simplify the build before...
To simplify the build before it went to MHP, we stripped down the 10-bolt to a more basic setup by removing the remaining sway bar and brackets, the entire CPP rear brake assembly, and the lines. A good wash removed years of grime.
At MHP, owner Manny Rodriguez...
At MHP, owner Manny Rodriguez got right to work and removed the factory differential cover with a 9/16-inch socket and drained the old rearend fluid into a pan.
Before we could dig in and...
Before we could dig in and remove the factory ring-and-pinion from the housing, Rodriguez checked the lash on the ring first with a dial indicator. We noted the reading at 0.007-inch lash and were well within the 0.007- to 0.010-inch recommended specifications. This meant our factory 10-bolt was still in great shape, and we could start the disassembly.
We first removed the main...
We first removed the main cap (passenger side), which allowed us access to the small set bolt that keeps the pin from dropping out of the spider gears. We used a 1/2-inch box wrench to remove the bolt along with the pin. With the pin removed, we gently pressed on the axle, removed the C-clip from the axle notch, and pulled out the axle. Note: Only remove one cap at a time; otherwise the entire assembly may fall out of the housing.
From there, we repeated the...
From there, we repeated the process on the other side by removing the driver-side main cap, C-clip, and then the axle. We then carefully removed the factory carrier assembly from the housing. Make sure the main caps are not mixed.
We used a large socket to...
We used a large socket to remove the pinion nut and used a brass punch and hammer to remove the pinion.
Don’t have an axle seal puller?...
Don’t have an axle seal puller? Rodriguez showed us a quick tech tip by utilizing the end of the axles to remove the seals. Once the seals are removed, we used a bearing puller to extract the old axle bearings, which we ditched since Moser supplies all-new ones.
Moser offers forged steel street axles for both the 10- and 12-bolt rearends. They are made from the same alloy as the race axles and are approximately 25-30 percent stronger than OEM (depending on spline count). These axles are nontapered, with hardened bearing seats and machined C-clip grooves to fit OEM applications. Plus, they’re available in any length up to 37 inches and can be shortened or resplined at a later time, should you choose to narrow your existing rearend. For our application, we ordered Moser’s axles in the stock 29 1/2-inch length in a 30-spline configuration.
Moser made upgrading any rearend...
Moser made upgrading any rearend simple with its setup kits. It includes the differential bearings (cups and cones), pinion bearings (cups and cones), pilot bearing, pinion support shims, adjustable pinion collar, pinion seal, nut, ring gear bolts, and even the gear-marking compound to complete the build.
Rodriguez installed our stock...
Rodriguez installed our stock pinion depth shim (located between the pinion bearing and the pinion head), pressed on the pinion bearing, and installed the crush sleeve. Before it went into the housing, we applied ample white grease to the pinion surface. To lock it in for final, we added the factory yoke and fastened it on with the supplied pinion nut.
With the old components removed...
With the old components removed from the housing, Rodriguez cleaned the inside of the case with solvent to remove any debris and material before the new bearings were installed. He then added the new pinion bearing races, bearings, and seals to the 10-bolt.
The Detroit TrueTrac was the first helical gear (no clutches) differential ever introduced into the aftermarket as an Eaton brand. In short, the patented design of the parallel axis planetary helical gears provides a quiet, automatic splitting of torque. It performs like an open differential under normal driving conditions and automatically transfers torque to the wheel with better traction. This limited-slip system responds instantly to torque feedback, anytime, at any speed.
Using a hydraulic press, Rodriguez...
Using a hydraulic press, Rodriguez applied pressure to the old pinion and was able to separate the factory bearing. We removed the stock pinion depth shim (located between the pinion bearing and the pinion head). Since the stock pinion depth shim is the correct thickness, it can be reused with the new components.
To install our new ring gear...
To install our new ring gear to the Detroit unit, we used the new bolts supplied by Moser in the setup kit. We applied red Loctite to the threads and torqued in a cross-tightening pattern to 75 ft-lb. Note: New Moser carrier bolts are lefthand threads.
We gently lowered the new...
We gently lowered the new carrier assembly into the housing and placed carrier shims between the carrier bearings and the rearend housing. Their job is to place a preload on the carrier and keep pressure against the bearings while the shim’s thickness on both sides also determines the amount of ring-gear backlash. It’s important to note that the backlash can be adjusted by changing the shim’s thickness side for side. To decrease backlash, we could increase the thickness on the left side while reducing the thickness an equal amount on the right side. To increase backlash, we could do the opposite. With the carrier in, we torqued the main caps to 65 ft-lb and made sure it spun freely in the housing. Note: The carrier assembly may have to be installed several times before the correct backlash is determined.
Moser’s gears are available for nearly any application and are CAD, CNC machined, and computer-control heat-treated to ensure the highest-quality product. Moser even offers a ring gear lightening program (add $100 to any set of gears) for serious racers to save precious rotation weight. The process involves machining a smooth radius on the outside of the gear and can save anywhere from 0.5 to 2.5 pounds. In our case, we ordered a set of Moser’s street/strip gears with a 3.73:1 setup.
To check we still had the...
To check we still had the correct backlash, we placed a dial indicator onto the ring gear and following the factory specs (0.005-0.010 inch) we determined our housing’s backlash was well within range at 0.007 inch.
Proper ring-and-pinion life...
Proper ring-and-pinion life begins with establishing the correct gear pattern. Identifying the wear pattern will signal if the backlash between the ring-and-pinion needs to be adjusted by swapping out different carrier shims. To do this, Rodriguez applied gear-marking compound onto the ring gear to identify the wear pattern. Spinning the gears produced a wear pattern that illustrated a majority of the gear contact was in the center of each tooth—exactly where it needed to be. Contact at the corners or edges of the teeth could break them and the backlash would have to be readjusted.
Once the new Moser axles are...
Once the new Moser axles are installed, we replaced the C-clips and added the axle spacer (replaces factory pin). Then, we installed the retaining cylinder and snap ring, making sure it had completely engaged with the groove.
A performance cover is one...
A performance cover is one of the single best things you can do to strengthen a 7.5- or 8.5-inch 10-bolt rearend. An integrated cap girdle helps stop gear deflection under load, which is caused by the main caps “walking”. To seal the deal, we bolted the custom Moser cover onto the housing, snugged the Allen studs against the main caps, and torqued them to 5 ft-lb. Then, we finished off the nuts with 10 ft-lb.
The Grab Bag
||30-spline axles (291/2 length)
||Setup kit/axle bearings, seals
||75W90 rearend fluid
Getting the rearend back in the Nova was a snap. We made sure to fill the rearend with 3 quarts of Synthetic Royal Purple 75W90 gear oil (for limited-slip gears) and put some miles on the gears before any competition. While at this year’s Goodguys Del Mar event, we noticed the Nova’s characteristics and personality have completely changed since our install of the Moser components; it’s like driving a new car. Wasted power that used to be directed to one spinning tire is now equally split between two. This translates into faster times through the cones and makes more use of the available power. We can even have a little fun in the turns now by sliding out the back end with some extra throttle. Plus, burnouts have become a lot more interesting. CHP