Written by Derek Putnam
Photography by Michael Fair and courtesy of the manufacturers
A team is only as strong as the weakest link, and the same can be said for a vehicle. Horsepower is plentiful in today’s market, with factory-built cars pushing north of 700 ponies with a warranty in place. But sometimes exercising those ponies will reveal parts that aren’t ready to be team players. Even classic muscle cars, with built engines, transmissions and rearends from the factory, can use upgrades to make them more reliable for street and track enjoyment.
Project Boulevard Boost, our ’70 Chevrolet Nova with a 925 rear-wheel horsepower blown big block powerplant, employed a factory Chevrolet 12-bolt rearend for over a decade. But as we increased its power levels, the once-reliable rearend would start to show some cracks in the foundation.
“The diameter of the ring gear is 8.875-inch on a 12-bolt,” JC Cascio of Strange Engineering said. “They can handle a decent amount of power and abuse, but stepping up to the bigger gear used by a Strange 9-inch Ford design or the S60 will definitely make a difference. Thicker teeth and more contact area help spread the load out more.”
So the decision to step up to one of Strange’s new rearends to handle the abuse was an easy choice. But which one would get the nod: the S60 or 9-inch Ford?
“The 9-inch Ford is the most popular all-around rearend we sell,” Cascio explained. “It’s followed by the S60, supported by a lot of bolt-in complete rearend sales, and finally the 12-bolt. The 9-inch Ford is the preferred choice for a racing application, with the widest selection of gear choices, the option of aluminum or iron cases, plus a lot of available parts, provide a lot of benefit for the 9-inch option.” But don’t count out the S60, Strange’s take on the popular Dana 60 rearend that supported many a Mopar vehicle in the 1960s and 70s. “We’ve always offered a version of Dana 60 rear end,” said Cascio. “About 15 years ago, we started using our own unique castings. The previous housing only would work on leaf spring or aftermarket ladder bar and four-link applications, and when we cast our own design, that allowed us to add versions for GM A-body and G-body platforms, plus the torque arm design for third and fourth-generation F-body.”
As popular as the 9-inch Ford is, the S60 makes a strong argument as a viable choice as well. “The S60 uses a 9.75-inch diameter gear, bigger than the 9-inch Ford does as well as coming standard with 35-spline axles. Prior Dana 60 castings uses shim packs to set backlash and preload on carrier bearings,” Cascio continued. “We went to an adjuster nut to replace the shim packs, allowing the user to use a spanner wrench to cut down on set-up and gear change time.”
The S60 also features 3-inch diameter, .25-inch wall thickness axle tubes, much better than most factory rearends. “A lot of factory rearends had the axle tubes pressed into the center housing and were plug welded,” Cascio admitted. “Strange welds the tubes 360 degrees to prevent twisting and leaking in that area.”
The only downsides to the S60 rearend? The lowest numerical gear ratio currently available is a 3.54, and it weighs a little more than the 9-inch Ford as well. “The increase in weight of the S60 versus a Ford 9-inch is somewhat related to the bigger ring gear,” Cascio said. “All told, a similar built S60 is about 25 pounds heavier than the 9-inch.” But of the three rearends Strange offers in both complete assemblies and parts, a similarly optioned S60 will cost less to purchase over the 9-inch or the 12-bolt.
After weighing out the options and prices, we made the decision to go with a S60 rear. Because of a few different parts we would be using in the build, Strange sent us a bare housing and the supporting parts we’d need to assemble it versus a complete ready to bolt in version. Rollins Automotive Speed and Custom got the call to set everything up, and we are quite pleased with the results. Part two of the build will feature an upgrade to disc brakes to complement the new rearend, and we plan to put both these upgrades to the test at the track soon.
Is Assembly Required?
Strange not only offers a wide selection of driveline and suspension components, but complete rear end assemblies based on the Ford 9-inch, Mopar Dana 60 and General Motors 12-bolt designs. But which route should you choose: a complete rearend, or buying the pieces and assembling it yourself?
“For street applications, the bolt-in rearends get the majority of the sales over individual parts,” said JC Cascio of Strange. “A lot of the sales for individual parts come from the racing market, especially 9-inch center sections.”
All the components we used for our S60 rear end are available in a completed rearend assembly from Strange, minus the leaf spring perches from Calvert Racing.
“The previous 12-bolt was set-up with these mounts,” said Jason Rollins of Rollins Automotive Speed and Custom. “They work a bit better with Calvert’s Split-Mono leaf springs, and we wanted to keep that constant in the build. But normally I’d recommend buying a complete rear end from Strange. All the guesswork is eliminated, and the quality is always top notch.”
Locking in Equal Traction
Sending equal power to both tires is the only way to ensure a consistent launch at the track. But many faced the dreaded clutch-type slip of Positraction units decades ago, as the only option in some cases was to upgrade to a spool, something most don’t recommend for a street car.
“It’s a safety concern,” said Cascio. “When taking a corner, the inner tire wants to turn at a slower pace. With a spool, that can’t happen. It can be easy to spin the rear end out, and from a parts standpoint, it puts a strain on tires, and puts additional pressure on axle flanges and bearings.”
Eaton now offers several choices for differentials, and the toughest one is the Detroit Locker. It offers 100-percent locking action to provide maximum traction to both wheels when needed, while unlocking when different wheel speeds are needed for cornering and tight maneuvers.
Making the Connection
After getting their start with rod ends, QA1 became a well-known name in the shock and suspension parts. Now, the Minnesota-based company is making waves in the driveshaft market, the first parts group from its advanced materials division.
“The new division is a vision of QA1 founder Jim Jordan,” said Damien Brase of QA1. Jordan first noticed carbon fiber being used in Sprint cars, and decided to embrace the material and bring it to the masses for street and strip applications.
“The driveshaft has to be able to deal with the torque upon launch, but then also for critical speed as you move down the track,” Brase explained.
The carbon fiber material allows QA1 to use a smaller 3.2-inch diameter size versus the larger diameter normally required for a steel or aluminum driveshaft. They accomplish all the winding and assembly in house and the winding of carbon fiber directly relates to strength.
“Every material has a spring rate,” said Brase. “With carbon fiber, the strength is directly related to the angle the fibers are wrapped at. A narrower angle of wrapping the material will affect torque more than critical speed versus a wider angle.” Combined with a weight savings over steel versions, it’s easy to see why more carbon fiber driveshafts are being used.
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LPW Racing Products
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Rollins Automotive Speed and Custom
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