Strange Engineering Rearend & Driveline Components Insight - CHP Insider
From the February, 2009 issue of Chevy High Performance
By Stephen Kim
Photography by Courtesy of the manufacturers
Jeff Strange of Strange Engineering
The next time you think you're having a bad day, be thankful you're not a rearend. In an era when anyone can build a 500hp small-block and have DOT-approved tires and cut sub-1.5-second short times, rearends endure a brutal existence. Fortunately, the days of scouring junkyards for a dwindling supply of factory 12-bolts are just about gone. With the aftermarket stepping up with quality rearends built entirely from scratch, hot rodders have more options than ever when it comes to driveline fortification.
Leading the charge in ensuring driveline reliability in your street machine is Strange Engineering. For more than 40 years, Strange has been a premiere manufacturer of quality aftermarket rearend and suspension components for applications ranging from street cruisers to professional drag-racing chassis. With bolt-in housings and rearend components for A-, F-, and G-bodies, Strange has the Chevy camp thoroughly covered. Although driveline parts haven't changed much in outward appearance since the '60s, the technology and manufacturing techniques that go into them have evolved dramatically. To get educated on these advances, we sought the expertise of Strange's Jeff Stange. Here are his tips on components selection, how to avoid common problems, and putting your money where it counts.
Junkyard Vs. New
Used rearends are often more than 20 years old and have seen a fair amount of abuse-not necessarily desirable in a performance upgrade. In addition to saving you the time and effort of digging in junkyards, another key benefit of aftermarket rearends is that they address the weak points of factory designs. "Our 12-bolt and S60 bolt-in rearends feature full 360-degree welds at the tubes and nodular iron or chrome-moly differential caps," says Jeff. "New rearends also feature 3.150-inch bearing and 1.5635-inch axle bearing surfaces, far superior to factory GM specifications. The castings we use for our 12-bolt and S60 rearends are cast from premium nodular iron and were designed to be more rigid through the use of computer modeling for improved durability and quieter and longer-lasting gears."
For many Bow Tie fans, brand loyalty takes a back seat to practicality when opting to run a 9-inch rearend. One of the 9-inch's benefits is the vast array of parts to chose from, but that can also add confusion to rearend building, especially when it comes to third members. Factory 9-inch cases were manufactured from gray iron and nodular iron. According to Jeff, nodular iron is 50 percent stronger than gray iron, which is a very brittle material. Junkyard 9-inch cases are very difficult to find these days, and he advises against using a non-nodular case for any of today's applications. "OEM nodular cases, which have an 'N' cast onto them, are fine for street cruisers but not for race cars," he explains. "All our iron cases are cast from premium-grade nodular iron and manufactured by us in the United States. There is no point in manufacturing an aftermarket case from gray iron or other inferior materials, when nodular iron increases strength by 50 percent and is far more ductile. Strange offers two types of nodular iron cases: The S-Series nodular iron case is recommended for applications up to 850 hp, and our Pro nodular iron case can be used on applications that exceed 850 hp."
There is a time and place to use aluminum in a street machine, but a rearend isn't one of them. Aluminum cases are hot in the street rod scene for aesthetic purposes, and they are plenty adequate for many moderate-horsepower street vehicles. However, other than looks, an aluminum case really has no benefits. "A nodular iron case is a much better choice for street use, and the weight break with aluminum is negligible," Jeff explains. "For a musclecar weighing more than 3,000 pounds, a nodular iron case provides a much better foundation for the rearend assembly. Compared to aluminum, a nodular iron case will provide longer gear life and quieter operation."
Although they're rarely used in street applications, floater axles have mechanics worth examining. A traditional axle is retained by a retainer plate, and the bearing by a locking collar. The axle flange hangs out of the housing 2.335 to 2.835 inches, so it becomes leveraged and stressed at the axle flange as well as at the bearing journal. Tire shake, torque, weight transfer, tire grip, and wheel and tire weight all stress the axle outboard of where the bearing sits. No issue for a Super Comp car, but for a Pro Mod car, this stress can result in axle failure. If an axle fails at the bearing journal, it will separate from the car along with the wheel. "A floater rearend solves this problem by using floater spindles, hubs, a driveplate, and a straight shaft," explains Jeff. "The straight shaft is splined on both ends, and one end slides into the spool while the other engages into the driveplate. This setup cures the leverage issue, and if the axle fails, the wheel is still attached to the floater hub. In a floater, the axle is not relied upon to retain the wheel; its only function is to drive the steel driveplate."
Gear WhineA whiney ring-and-pinion set can make an otherwise pleasant freeway cruiser unbearable to drive, so how do you avoid the noise? "Certain rearends are more prone to noise than others," says Jeff. "For instance, a 7.5-inch 10-bolt is far less forgiving than a 9-inch rearend, partly because of gear size and partly because of the rearend design. Also, some gear ratios are more prone to noise. When a new gearset is installed, it should be set up like a brand-new assembly with new shims, bearings, and ring gear bolts, which will significantly reduce the potential for whine."
Ring-And-PinionAftermarket ring-and-pinion sets, in most cases, are no stronger than OE gearsets. The advantage of aftermarket gearsets is their wider range of gear ratios. In some cases, aftermarket companies use a better material, but the difference is subtle. "The true quality of the gear is evident in how well the gear sets up and how quiet the gearset is in operation," Jeff opines. "Competition gearsets are designed for drag racing only, and are manufactured from 9310 steel, a high-impact material. This type of gear is excellent for abusive drag racing but would be too soft for daily driving and would wear out very quickly. Street gears are mostly manufactured from a harder 8620 steel, which is better equipped for constant use."
S60 Rearend"A few years ago, we created the S60, a proprietary casting based on the 12-bolt's architecture that is designed to accept Dana 60 components," Jeff says. "We have cast different centers for vehicles like the A-, G-, and late-model F-body to create bolt-in rearends for several GM applications. The S60 has several advantages over a 12-bolt or 9-inch. It is equal to the 9-inch in strength, and both the 9-inch and S60 are far stronger than a 12-bolt. Also, a lot of OEM Dana 60s were equipped with 35-spline axles, which means you have the option of running either a Traction-Lok, Truetrac, or Locker differential. So if you do not like how a Locker behaves on the street, you can use a very smooth and quiet 35-spline posi unit. The S60 easily adapts to ABS and traction-control systems found on late-model F-body cars and is only about 15 pounds heavier than a comparable 9-inch."
With all the different rearend fluids on the market today, making an educated purchase can be difficult. Jeff says not to be persuaded too much by marketing hype. "We get to see the burned bearings and burned ring-and-pinion sets that are a consequence of many of the special rearend fluids used these days," he says. "We recommend regular petroleum-based oil 85/145W, and while we don't sell oil, we have been very happy with Lucas rearend oil. We do install oil pumps into our Top Fuel rearends, but this is to reduce oil capacity and static weight. As far as fluid that reduces a measurable parasitic drag, we are not privy to any meaningful data."
"The two basic types of axles in our industry are thru-hardened and induction-hardened," Jeff says. "There are major differences between a dedicated drag racing axle and a street axle. Drag axles are made from hy-tuf, an alloy composed of low-carbon, high-manganese, high-nickel, high-molybdenum steel content. This type of axle is heat-treated in a vertical furnace to a hardness of 46-48 on a Rockwell scale and is the same hardness from the center of the shaft to the surface of the shaft [thru-hardened], resulting in superior torsional strength and ductility. However, it should not be used for street applications since it is not designed to take the stresses of bumps, potholes, and railroad tracks. On the other hand, street/'strip axles are induction-hardened, a heat treatment that yields an extremely ductile axle. These axles have a high carbon content and achieve a surface hardness of 58-92 on the Rockwell scale. The combination of material and heat treatment creates an axle that can survive the bending loads inherent in street use."
12-Bolt Vs. 9-Inch
"A 9-inch rearend is a poor choice for cars that utilize torque arms, such as the late-model F-body, mostly due to the substantial increase in road and driveline noise through the torque arm itself," says Jeff. "Also, the 9-inch does not adapt well to ABS systems. This is why we don't make a 9-inch rearend for late-model F-bodies. For these cars, the 12-bolt is a significant upgrade over the factory 7.625-inch rearend. For earlier F-bodies and other non-torque-arm GM vehicles, the 9-inch provides an excellent foundation. The only notable con for the 9-inch is that axles with 35 or more splines require a Detroit Locker or a spool, which some people do not like to use. Lockers also make for a pricier rearend. Likewise, the driveshaft has to be narrowed or replaced when using a 9-inch, as opposed to a 12-bolt that allows retaining your stock driveshaft. However, if your application requires a replacement rearend, then it certainly requires an upgraded driveshaft."
Perhaps due to its extensive use in high-end drag car chassis, chrome-moly has a certain mystique in automotive applications. However, coughing up extra dough for a chrome-moly rearend housing probably isn't necessary for most applications. "Steel axlehousings and tubes are made from either mild steel or chrome-moly, but the vast majority are made from mild steel," says Jeff. "Housings made of mild steel provide adequate strength for most drag racing applications, and every street and drag racing steel housing we manufacture is made from mild steel. Most of the housing's strength is derived from its tube size, back brace, basic housing design, and how it is welded together. The aforementioned points are far more important than the difference between chrome-moly and mild steel."
Whether it's due to unclear rulebooks or hard-headed racers, there seems to be a fair amount of confusion when it comes to selecting the right wheelstuds. Ideally, use the shortest wheelstuds possible. Shorter studs are lighter, allow easier wheel removal, and do not experience the same leveraging loads as longer studs. "There are two common aftermarket stud sizes, 1/2x20 and 5/8x18," says Jeff. "We offer 2- and 3-inch-long 1/2-inch-diameter studs for street or mild drag use, but do not recommend a 1/2-inch stud longer than 3 inches for safety concerns. For dedicated drag racing vehicles, 5/8-inch studs are highly recommended. Since 5/8-inch studs, unlike 1/2-inch studs, do not use conventional lugs, it is important to make sure that wheel thickness, rotor hat thickness, and any wheel spacers being used are compatible with 5/8-inch studs."
"Forgings are mostly used to reduce machining time and scrap metal," explains Jeff. "However, a forging also provides excellent grain flow of materials, which is superior to billet components. When we first started making axles in the late '60s, we used two pieces. One piece of 7-inch-diameter steel for the flange and one piece of 2-inch-diameter steel were welded together before machining the shaft. Today, we manufacture our axles from premium-grade forgings, then have dedicated CNC lathes for rough-turning and finish-turning the axles. Up until the late '90s, we fully ground the bearing surface and axle flange, but with today's tools and machinery, we are able to hold exacting tolerances and provide an excellent finish with our dedicated CNC lathe. Less than 10 years ago, we used manual multispindle drill presses to drill and tap the bolt-circle pattern and manual hobs to hob the axle splines. Today, we have dedicated CNC vertical mills and a CNC hob, which are far faster and more accurate. That means lower prices and better quality for our customers."
To make sure your axles stay put, C-clip eliminators are something every street/'strip vehicle should have. "Most sanctioning bodies, such as the NHRA and IHRA, have rules that specify an e.t. or trap speed at which the use of a C-clip eliminator kit is mandatory," explains Jeff. "However, I would recommend a C-clip eliminators kit for any application that has been enhanced beyond its factory performance. Remember, if the axle or the side gear fails with C-clips, the entire axle will slide out of the rearend."