Picture this: the planets have aligned to bring together the perfect combination of sticky track, sticky tires, and your fresh bitchin' big-block. After heating the tires and staging, the lights come down and you drop the hammer. Instead of launching, there's a horrible bang from behind, and you ain't goin' nowhere. Congratulations friend-you just broke your junk, and made a huge mess on the track. We've seen it a hundred times, and it's still not cool. Slightly less embarrassing, but just as inconvenient, are those untimely episodes on the street where wheel hop snaps axles and breaks rearend gear teeth. Ouch!
Our Street Sweeper '68 Chevelle project is the type of car-heavy and (soon to be) powerful-that is a prime candidate for this kind of misbehavior. Endowed from the factory with GM's corporate 8.2-inch 10-bolt rear, this Malibu would be headed for a date with the tow truck if it were to encounter the 600-plus horsepower big-block we're planning for it. And while our Chevelle may indeed find itself on the wrong end of the hook some day, it won't be from an exploded rearend-thanks to all-new hardware we're getting from Currie Enterprises.
Before making our move to Currie, we weighed our options carefully. One of our first ideas was to go with a '71-and-later 10-bolt, which has the larger, stronger 8.5-inch ring gear (the same rear that's in our lighter and less powerful '76 Camaro, Project g/28). Although it's super cheap, it would still require modification with a stronger differential and axles. Even in the best case, it would be marginal in a 3,800-pound car running 11s.
We quickly opted to leave the game of rearend roulette to Car Craft. A GM 12-bolt is far stronger, and is well supported by the aftermarket. It's a good choice that's up to the task, but the decision to go with a Ford 9-inch was based on one more fact: For about the same price as a built 12-bolt, we could get a built 9-inch with all new parts. The Ford 9-inch rear is significantly different than either the 10- or 12-bolt; instead of having a cast iron center section that has steel tubes wedged and welded to it, the entire housing is formed steel, from end to end. The third member of a Ford 9-inch is not burdened by the torsional loads from the axle tubes, and can easily be removed for maintenance. Additional third members may also be set up with different gear ratios or differential types, for smooth swapping at the track-no need for shim packs, dial indicators, or crush sleeves. On the downside, there's a small penalty in mass and mechanical efficiency relative to the GM 12-bolt.
Currie-Built Crate Rearend
If you're serious enough to consider a bomb-proof rearend like a 9-inch, you likely have a pretty good idea of what you need, and how much you want to spend. Surprisingly, that is a pretty good argument for not buying a ready-made, pre-assembled unit. (Why buy stuff you don't need, or leave out something you do?) The Currie-Built Crate Rearend comes to your door unassembled, via UPS. The advantage of this is twofold: You don't have the added cost and inconvenience of having your rear shipped by truck freight (the individual parts are below the UPS weight threshold), and you don't have to wait weeks or months for it, since Currie plucks the parts off the shelf the day you order it. If you don't mind waiting, Currie can ship your rearend assembled, but it will take three weeks instead of the two to three days it normally takes to ship modular kits.
Options
Currie Enterprises offers a choice of standard or big-bearing pinion support third members. These can be loaded with an open diff, a spool, a Detroit Locker, or a Detroit TrueTrac. Depending on your situation, you can order your rearend kit without brakes, with drum brakes, or with a selection of disc brake kits. In addition, all 9-Plus housings include a pair of Currie's track-tested 31-spline 9-Plus axles.
We chose a Currie Crate Rearend with the nodular third member because we intend to use it a lot at the track. We might get by with the standard third member, but for about $390 more, we like the added insurance for a heavy A-body. The next choice we made was the differential, and we opted for one of our favorites: the Detroit TrueTrac, which adds about $280 over the cost of a spool. The Detroit TrueTrac offers all of the benefits of a limited-slip diff, without the wear issues of a clutch-type posi. And unlike a locker, the TrueTrac's operation is transparent on the street.
Currie offers a selection of rear brake kits, and while we would eventually like to do some serious open-track work down the line, we felt a more typical street/strip selection would be Currie's 11-inch drum brake system for $349.95. At this point, our total parts bill was $2,896.20, including the housing with A-body suspension brackets mounted, 9-Plus axles, Sportsman nodular third member (with 3.70 gears), TrueTrac differential, and 11-inch drum brakes.
The options might sound complicated, but Currie's Web site, Crate-rearends.com, makes it easy-no joke. Click on your intended application, and follow the prompts for the various options. The site keeps a running tab of your selections and the prices, including the total. Order it all at one time, or part-by-part as finances allow-you have that choice with a modular system like Currie's. We played with the order calculator, and figured the low-end of the range at around $2,329 (a Crate Rearend with 31-spline forged alloy axles, a stock third member, a spool, 3.70 gears, and drum brakes), and $3,446 for a maxed-out unit (with the Sportsman third member, TrueTrac limited-slip differential, 3.70 gears, and Wilwood 12.5-inch disc brakes with polished calipers and drilled rotors).
Currectrac Control Arms
Currie's product line also extends to rear suspension components, and after examining their CurrecTrac rear control arms for GM '64-72 A-bodies, we went for the adjustable upper arms (PN CE-7011D, $299.95), and the lowers (PN CE-7011L, $224.95). We've planned all along to upgrade the rear control arms because the stock stamped-steel pieces are prone to flex under hard launches. Boxing the stock pieces is an alternative, but it doesn't adequately address the deformation of the bushings at our intended power level. We could install harder urethane bushings, but the improvement in suspension geometry under load would come at the price of driveability, and wouldn't offer the necessary adjustment for pinion angle.
The CurrecTrac control arms take care of all the issues-flex, bushing deformation, driveability, and pinion adjustment-but perhaps the most significant problem-solver is Currie's unique "Johnny Joint." (No, they didn't name it after me.) Most aftermarket control arms use urethane bushings to reduce or eliminate deflection under load, but the resulting inability to twist, roll, or pivot causes unwanted bind. This bind produces noise, harshness, and in extreme cases, non-linear handling when used in a triangulated four-link system (such as the GM A-body). The Currie Johnny Joint sandwiches an articulating steel ball-much like a Heim joint-between two urethane bushings, which are captured in a tube at one end of the control arm. Unlike a Heim joint, which is steel acting directly on steel, the Johnny Joint has the ability to absorb and dissipate road rash, while still offering the multi-axis freedom that a standard urethane bushing cannot. It's an elegant solution, which takes care of all related concerns-and Currie's the only company that's got it.
Current Status
We started out by getting our Chevelle looking good with wheels, tires, and SS stripes. That was followed by some much-needed help for the front suspension. With the poor 10-bolt now banished from the car, and the rear control arms up to snuff, we are ready to concentrate on other weak areas. If we're going to run 11s, we'll need some power from a mild street-roller 468 big-block, a fuel system to supply it, a decent cooling system, a high-flow exhaust, a trans and converter, and some basic safety equipment. We're still six to eight months away from hitting the track, so stay tuned as we transform our '68 Chevelle into the ultimate street fighter-all while keeping it rolling on the street.
9-Plus Gear Ratio Choices
3.00
3.25
3.50
3.70
3.89
4.11
4.30
4.56
4.86
