Nova Rearend Build - In The Rear With The Gears

Building the Much-Maligned 8.2-Inch 10-Bolt Into A Diff That Can Live

John Nelson Mar 17, 2008 0 Comment(s)
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Before diving into the details of this 8.2-inch 10 diff build, we figure we should address a couple of questions that are sure to pop up. First of all, the 8.2-inch 10-bolt rearend came in Chevy and B-O-P (Buick-Olds-Pontiac) versions; for our purposes, that means it was found in '62-67 Chevy II/Novas and various Novas, Chevelles, and El Caminos through the '72 model year. Question two, which follows quickly and more vehemently, is, "Why would you build one of these things?" So we'll explain the why and what we did to make this thing a viable dragstrip diff.

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Our first order of business, of course, was to disassemble the 8.2-inch 10-bolt donor rearend that we would rebuild for dragstrip duty in Dave Stoker's intrepid '67 Nova. This original open carrier wasn't too bad off, but the bearings did show wear and pitting. The cross-shaft was hammered-Rick Galloway had to drive it out with a punch, unlike the C-clips, which just fell out of place. Except for the C-clips and the carrier shims, this assembly is off to the junk pile.

The why of this story follows the idea that it's cheaper to build up what you already have than to buy something else. Would a 12-bolt or a 9-inch be stronger? Absolutely, but a full new replacement setup for our subject '67 Nova would cost at least $2,000. We did find a few used 8.5-inch 10-bolts and 12-bolts during some online searching, but not many-and they were of indeterminate quality. Someone looking to make this swap with used parts would have to factor in the costs of a rebuild and retrofit in addition to whatever was paid for the core diff.

Dave Stoker had all this in mind when it came time to rehab the rearend in his 11-second '67 Nova, a car that gives off no external evidence of its dragstrip prowess. When it comes to cost, Stoker tells us that a core 8.2-inch 10-bolt fetches about $150, if not less, on the open market. Stoker certainly had cost considerations in mind, but he was also looking to keep a Nova rearend in his Nova, as well as maintain its sleeper persona-right down to its bantamweight diff.

Ironically, the diff that needed replacing was the victim of a faulty posi unit, not the small-size differential itself. With this in mind, our first move was to raid the Eaton catalog for PN 19603-010, which is a limited slip differential for '64-72 Chevrolet 8.2-inch 10-bolts with 28-spline axles and 3.08-or-steeper gears. Obviously, we wanted both wheels a-turnin'. On the other hand, Eaton posi units come filled with forged gears and carbon friction discs that will handle the 11-second abuse we'd be throwing at it.

Our second call was to Randy's Ring & Pinion. If you call Randy's for tech support, you'll probably be talking to Terry Burg, as we did. In short, we looked to upgrade every piece we could. The Yukon Gear ring-and-pinion set we chose (in the Nova's original 3.36:1 ratio) is made to be stronger than OEM gears while running as quietly as a stock set. The 1541H steel axles we chose are 25 percent stronger than OEM pieces, according to Randy's. We also ordered a master rebuild kit, which comes with Timken bearings to ensure strength and durability.

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With the axles and ring carrier removed, Galloway proceeded to the pinion yoke. If you don't have a puller, he suggests removing the yoke using an air hammer with a point, rather than a hammer and punch, to avoid damaging the pinion assembly. If you're not reusing the pinion, this is less important. We weren't looking for unnecessary carnage, so we did it the clean way.

Burg went a step further, strongly suggesting we run a rear girdle rather than a stock cover. "The higher the horsepower level, the more it wants to shoot a bearing cap out the back," he explains. "And this is a small ring-and-pinion with small bearings and carriers." The cover Randy's provided reinforces the bearing caps against just such an occurrence. "It's one of the best things you can do with these small rearends," Burg tells us.

Of course, all these high-grade parts can go for naught if a rearend isn't properly set up, and that's where Don Lee Auto Service comes in. Don Lee tech Rick Galloway has set up more than a few diffs, many of them in heavily abused off-road vehicles. The bottom line here is to take your time and set up the gears correctly-it's the best way to ensure longevity for any rearend.

So what did we get for our efforts? First of all, Stoker reports that this rearend is indeed quiet, a testament to the gearset quality and the professional setup. But more importantly for our purposes, we of course took a trip out to Irwindale Speedway to test our handiwork and saw a nice drop in 60-foot times from a not-too-shabby 1.64 to an even better 1.565. But will this diminutive diff live? We'll let you know, since we've got more straightline fun planned for this slick Nova. In the meantime, check out the highlights of this 10-bolt build.

QUICK NOTES
The Task
Assemble an 8.2-inch rear that can survive in an 11-second Nova.
Bottom Line
It takes less power to move a small ring-and-pinion. Use quality parts, set it up correctly, and reinforce the carrier bearings, and it will survive.
Cost (Approximately)
$1,450

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The pinion bearings come out easily enough, but the bearing races must be driven out. The 10-bolt architecture conveniently provides notches, allowing the races to be knocked out with a punch.

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The new gear carrier bearings had to be pressed onto the Eaton limited-slip we utilized for this build (background). While he was busy pressing bearings, Galloway took a moment to press the bearing off our 8.2-incher's original pinion. His goal was to obtain the pinion shim, which would be used later as our starting point for setting pinion depth.

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The rearend rebuild kit from Randy's Ring & Pinion contained everything we needed for the job at hand, including marking compound, two different crush sleeves, a shim pack for setting gear backlash, and top-quality Timken bearings. We only had to pick up new axle bearings and seals to be fully equipped.

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Skipping ahead a bit, Galloway had emptied the 8.2-inch housing of all its innards and thoroughly cleaned it. As we prepared to reconstruct our beefier 10-bolt, he laid out the correct tools. A proper bearing installation tool guards against damage when driving in new races. It also makes the job much easier.

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Before mating a new ring to its carrier, Galloway always runs a file lightly over the gear's backside to remove any burrs. The ring was then joined to the carrier with the provided bolts. Each fastener was dabbed with Loctite and torqued to 55 ft-lb.

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Once our new Eaton LSD (limited slip differential) was outfitted with its new ring gear, Galloway set it into the housing, using the original carrier shims as a starting point. Gear backlash should be set at 0.006 to 0.010 inch. Getting there is a trial-and-error process-in fact, this shot is of Galloway's second attempt. Using the original shims yielded only 0.002-inch backlash; reversing them made it 0.015.

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Galloway turned to the shim packs contained in our master rebuild kit. In short, increasing shim thickness on the left side decreases backlash; doing the opposite increases it. And remember, when you change the shim thickness on one side, a corresponding increase or decrease must be made on the other. Galloway carefully measured each side and used the kit to create the proper shim thicknesses.

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This setup, which was our fourth, proved to be the winner, yielding 0.007-inch backlash. According to Galloway, our diff-building talent for the day, there's no substitute for this process if you want to end up with a properly built, durable, and quiet-running rearend.

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Once backlash was properly set, Galloway moved on to pinion depth. As we mentioned above, this rearend's original pinion shim was installed on our new pinion, as was a checker bearing, which conveniently slips on and off the pinion. After brushing on the marking compound and rotating the gearset, we got a near-perfect pattern. The contact should occur in the center of each tooth, which is exactly what this pattern shows.

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In the home stretch, Galloway disassembled our 10-bolt subject for the last time. The checker bearing was removed from our new pinion, allowing the new pinion to be pressed on with the original 0.028-inch-thick shim. Also note the difference in crush sleeves. Our new pinion uses a smaller sleeve (left), which Terry Burg at Randy's Ring & Pinion told us is just "new technology replacing old."

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With that, it's time to put this puppy back together. It took some effort to get the yoke onto the pinion splines (a plastic hammer is good for this). Once there, the pinion bolt gets 12-15 in-lb of torque. The bearing cap bolts, which are being tightened here, get 60 ft-lb each.

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Galloway then brought in an extra set of hands to install our new axles, which he'd already fitted with the new studs Randy's included. The axlehousing had been equipped with new bearings and seals (using the proper driver, of course). This part is pretty standard-remove the cross-shaft bolt, pull the shaft, slide in the axles, install the C-clips, replace the cross-shaft, and voila, you're done.

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Except, that is, for installing a beefy rearend girdle. These aluminum covers are much thicker than stock and use bolts to preload the bearing caps, guarding against their violent expulsion under duress. All that remained was to spray on a coat of fresh paint and bolt this baby into its new home. Although our subject Nova's owner had doubts about how well the new cover would fit under his ride, everything went into place nicely. With a new posi and gears in place, it quickly became evident that this Deuce hooks better than ever-and will hopefully do so for some time.

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