Rear Ready! Components and Information for Upgrading Your Rearend and Axles
Unless you have a tricked-out show car or vintage hot rod, chances are you haven’t paid much attention to your vehicle’s rearend assembly. You likely know the gear ratio or perhaps bolted a chrome cover on housing, but for the most part, the rearend assembly just doesn’t get a lot of love when it comes to bling and performance capabilities.
However, there’s a lot going on underneath the back of your cruiser, from the gear ratio, to the style of differential, axle types, limited-slip capabilities, and even the entire axle assembly, and all of those elements can be significant to the overall performance of your vehicle. The good news is that there are plenty of companies that focus entirely on the rear axle assembly so you can easily outfit your hot rod with the right parts to fit your driving, handling, and performance expectations.
From complete, ready to bolt-in ‘crate’ rearend assemblies, to gears, axle types and independent rear suspension housings, there are plenty of options and new setups available to get you in gear and on down the highway.
Cool and Quick
Quick-change rearends have been a favorite of hot rodders and racers for decades. The benefit, as the name implies, is how quickly the drive ratio can be changed with two easily accessible rear-mounted spur gears. For example, you could have a cruise-friendly 3.48:1 ratio, then simply swap the location of the two gears to achieve a 4.11 ratio for the strip. Today, the quick-change remains a favorite for hot rodders and is also at home on racetracks, where it’s often used on sprint cars, dirt modifieds, and even the autocross.
Winters Performance has been manufacturing speed parts since 1958 and can assemble a quick-change for everything from traditional rods to pro touring muscle cars and trucks. They offer solid axles and independent versions that are available in two sizes; the V8 model with an 8-3/8-inch 3.78 ring and pinion (rated to 600 horsepower), or the Champ series with a 10-inch 4.12 R&P (rated to 1,000 horsepower). They offer quite a range of axle bell styles, gear covers, and finishes, too.
Drag racers have relied on the Mark Williams modular aluminum rearend housing for years. These housings are designed to accept 9-inch components and have continued to be refined for improved strength and performance over the years. Their modular design is available with half-dozen CNC-machined aluminum end bells to provide a variety of wheel-to-wheel widths as well as 3-inch steel tubes to fit any chassis width. If you prefer a 12-bolt, M-W also manufactures a modular aluminum rearend for Chevy applications.
Speaking of the GM 12-bolt, M-W offers several complete 12-bolt assemblies ranging from a hardcore Pro model with 35-spline axles and a spool, to Street/Strip models with 30-spline axles, an Eaton posi, beefy gears, pinion yoke, and more for ’64-’77 A-bodies, ’78-’88 G-bodies, and most leaf spring cars.
Looking for an easy way to turn your peg-leg open rearend into a two-tire shredder? Summit Racing offers a full line of Positraction Differential Carriers that deliver aggressive yet controllable traction.
Each carrier features a nodular iron case filled with forged steel internals with the strength to handle plenty of torque. Summit offer a long list of fitments, including the Ford 7.5 and 8.8, GM 10-bolt axles including BOP models, the popular GM 12-bolt for cars and trucks, the 8.5 Corvette, DANA 60 and the Chrysler 9.25. Don’t be embarrassed any more with a one-sided burnout, give Summit a call.
The axles of all solid rearends are connected to the differential gears through splines machined on the ends of each axle. The strength of an axle, or its holding capability, is based on not only the diameter and material used, but also the spline count. Mark Williams Enterprises recommends a 35-spline axle over the factory 28- (GM) or 31-spline (Ford) for high performance street applications.
Also note that all splines are not created equal, with variances in the pressure angle of the spline or the shape with straight-cut or slightly curved. When assembling a higher performance rearend, go with more splines, and make sure the axles are compatible with your differential.
Go with a Crate
When you make the decision to step up to a popular Ford 9-inch rearend, you can put one together piece meal but you may end up with a lot of parts that don’t work together. For example, not all brake kits are compatible with every 9-inch housing, plus there can be different bearing types, axle flange diameters, and more. You can save a lot of time and headaches by reaching out to Currie Enterprises to order one of their crate rearends.
Currie offers direct bolt-in 9-inch Ford rearend assemblies that will have all of the brackets welded in place along with being the proper width for your specific application. From there, they’ll outfit the unit with a carrier that is best for your application, such as their TwinTrac differential that provides two-tire fire in a straight line, but allows easy turning without any chirping or clicking (plus they don’t require a friction modifier). You’ll get the gears you want with the brakes that fit all in a ready-to-bolt-in assembly.
Whether you need to update your rearend to handle more power, or are in middle of a fresh build, Speedway Motors can get you handled. Speedway offers a custom-built Ford 9-inch rearend that they fill with high-quality components and ship to you ready to install.
Speedway starts with a fabricated steel 9-inch housing fitted with forged 31-spline axles. From there, they assemble a nodular iron third member with your choice of gears and install a Powertrax Grip Pro differential that is ideal for light- to medium-weight street machines. This unit is ideal for the street thanks to its quiet operation and its limited slip performance. The kit is supplied with gaskets and necessary hardware.
Planning to rebuild or upgrade the differential or ring and pinion in your rearend? Eaton now offers a line of Master Installation Kits that are supplied with all the parts you need to refresh your rearend. Each kit is supplied with premium bearings and components to ensure long life and quiet operation for miles to come.
Eaton’s kits are available for a number of popular axles including GM, Chrysler, the 9-inch Ford, and even Jeeps. The kits are available to help with the installation of Eaton’s family of aftermarket differentials, including the revered Positraction, Detroit Truetrac, Detroit Locker, and the ELocker.
The gears of a rearend have a tremendous influence on the amount of engine torque that is transferred to the rear wheels, as well as the rpm while cruising down the road. One of the benefits of a quick-change rearend is the ability to easily change the gear ratio in a matter of minutes.
A quick-change has two spur gears, a top and a bottom, with the bottom being driven by the driveshaft. With a 1.105 spur gear set (Speedway Engineering’s #25) you could go from a cruise-friendly 3.72 to an acceleration-enhancing 4.54 simply by swapping the location of the two gears. If the quick-change were equipped with a 1.240 spur gear combo, you’d have options of 3.40:1 or 4.98:1. If your vehicle pulls double duty on long cruises as well as the autocross or drags, a quick change could come in handy!
IRS for All
Pondering the benefits of an independent rearend for your street rod or pro touring machine? Dutchman Motorsports can help with a complete IRS assembly, or if you prefer to assemble your own, just pick up their heavy-duty lightweight housing and a set of 31- or 35-spline axle shafts. In short, Dutchman has you handled when it comes to a trick IRS (or other solid axle needs as well).
With over 30 years of experience built into their hub-to-hub IRS assemblies, Dutchman has continued to refine and improve their housing, which is cast and heat-treated in the USA. The aluminum assembly can be fitted with yoke/u-joints, or go with heavy-duty CV shafts for any track width. Timken tapered roller bearings are used along with 33-spline outer stub axles and finished with a Dutchman-built 9-inch third member.
Looking for new set of gears for your 9-inch rearend? GearFX, located in Mooresville, North Carolina, specializes in third member assemblies that are ideal for pro touring builds and racing. Their N-series Ford 9-inch rear gear assemblies are based on a Ford Racing nodular iron case cast specifically for GearFX from the Ford molds. Each case utilizes exceptionally strong chromoly bearing caps, Ford Racing Daytona pinion supports and seals, Timken bearings, and ARP hardware.
When you’re getting really serious, GearFX offers additional options including REM isotopic surface finishing and a dyno break-in service for increased performance, durability, and trouble-free operation. All GearFX rear gears are individually inspected and hand deburred to meet their championship-winning standards and attention to detail.
High Tech Vintage
The venerable quick-change rearend has been a staple in traditional hot rodding since the 1950s and is still the choice of many rodders and racers. Having the ability to change the final drive gear ratio in a matter of minutes is a huge advantage for racers and one company that knows the ins and outs of the quick-change is Speedway Engineering.
Speedway Engineering manufactures several different quick-change rearends, including a popular unit that is designed for early Ford bells and has about three dozen ratio options available. They also offer IRS center sections with a number of different flanges to accommodate different half-shaft options. For higher output applications such as pro touring builds, the beefy 10-Inch quick-change is a great choice with gear sets ranging from 2.19:1 to 7.71:1.
Many axles, such as those used in the Chevy 10- and 12 bolt rearends, as well as the popular 8.8-inch Ford, are retained by a simple C-clip that is recessed in the carrier and held in place by a cross shaft. However, if there is an axle failure, there is nothing that will hold the shaft in place, meaning the entire wheel (and broken axle stub) can come out and off the vehicle.
Many companies offer ways to do away with these potentially problematic clips, like this C-Clip Eliminator Kit from Strange. It bolts to the stock rearend housing to secure the axle in place, even in the event of an axle failure. These are mandatory in many forms of motorsports.
Sure, you can take a chance on a used axle housing to rebuild to your specs, but for just a little bit more you can start with an all-new housing from Strange Engineering and have it filled with even stronger internals. Strange has been in the rearend game for years with an emphasis on racing, but they also offer a full complement of bolt-in or custom rearend assemblies.
Strange offers their S60 (Dana 60), the Ford 9-inch, and even 12-bolt rearends that can be ordered in a variety of combinations to suit anything from stock-style restorations to high-horsepower street/strip monsters. The 9-inch can be had with 28-, 31- or 35-spline axles with a Tru-Trac, S-Trac, or lockers with third member options in iron or a through-bolt aluminum case. Complete direct bolt-in rearends are available for popular domestic applications.
One of the most important components to choose when updating your rearend is what kind of differential is best for your application. PowerTrax understands the importance of traction through having both tires gripping yet knows there needs to be cornering capabilities as well as a smooth, quiet operation. This is exactly why they offer a number of different traction-adding differentials.
The PowerTrax Grip LOK is a mechanically actuated traction control that provides the strength of a spool when you need it but with smooth operation around corners. The Grip PRO uses 3×2 spiral gear technology to deliver progressive traction through throttle input while their Grip LS is a clutch-type differential in a forged steel case. For straight-line and heavy-duty off-road abuse, the PowerTrax Lock-Right is ideal.
Kugel Komponents is known for their attention to detail and quality of their products and with a few land speed records to their credit, the company’s R&D department is quite serious. In short, they understand how to build function into a beautiful form, which is exactly what you get with the Kugel Independent Rear Suspension system.
Kugel’s IRS is based on their own cast aluminum housing fitted with Corvette bearing assemblies and accepts a Ford 9-inch third member. The assembly is surrounded by fabricated tubular control arms, dual or quad coil-overs, inboard brakes, and filled with nearly any gear ratio. The IRS is available in a natural finish, polished, painted, or even powder coated, and will be fully assembled with a basic pre-alignment calibration and ready for installation.
Tech Tip #4 – What’s your Ratio?
If you’re not quite sure what gear ratio is in your car, you don’t need to remove the cover or third member from the axle. Richmond Gear explained that all it takes is a jack, some chalk, and a little counting.
With the rear wheels safely raised and secured, put a mark on the driveshaft and the rear tire. Place the transmission in neutral and slowly rotate the tire one complete revolution while someone counts the rotations of the driveshaft. The number of driveshaft revolutions for each tire rotation will produce an approximate representation of the ring-and-pinion gear ratio. For example, if the driveshaft turns just a hint over three turns, the ratio is similar to a 3.08 gearset. If it was three and three-quarters turns, it is probably a 3.73 ratio.
Also note that if the opposing wheel spins in the opposite direction, the axle is equipped with a limited slip. If the wheels spin in the same direction, you have an open differential (the one-wheel peel).
One part that is probably due to be replaced on an old muscle car or truck are the axles. Over time, seals cut grooves into the axle shaft, bearings wear, and things tend to get bent or punished. Upgrading to a fresh set of Moser’s direct-fit replacement axles will ensure you have a strong and true connection between the differential and the wheel.
Moser offers a wide variety of stock replacement axles for most popular GM, Ford and Chrysler muscle cars and trucks. The new axles are made in the USA with premium quality alloy steel with concise splines and are available for 10- and 12-bolts, 8.8 and 9-inch Fords, 8¾-inch Mopars, and others. If you haven’t considered an axle update, it might be time and Moser has you covered!
Some hot rodders enjoy a loud exhaust and the mechanical notes a vintage car can bring, while others prefer a quieter ride in the cabin. John’s Industries worked closely with US Gear and their new Stealth Series of high performance ring-and-pinion gears for the popular Ford 9-inch rearend to produce one of the quietest rears available for the performance industry.
The Stealth gears utilize advanced gear cutting technology, known as face hobbing, that creates a continuous and more consistent cut on all the teeth of the ring gear and pinion gear at the same time. This maximizes tooth contacts, giving a wider pattern, resulting in a whisper-quiet differential with cutting-edge performance, plus an easier setup. Contact John’s for a complete and quiet rear axle or third member.