Recently, we have observed an increasing number of "three-quarter-ton" quick-change rearends showing up under street rods. This style of heavy-duty quick-change has been used in oval-track stock car racing for more than five decades. Current NASCAR-style cars use a floater rearend that is based on a Ford 9-inch design and is not a quick-change, but the weekend warriors of outlaw-style, oval-track stock car racing continue to put the horsepower to the ground via the three-quarter-ton quick-change.
The earliest forms of these rearends were created from three-quarter-ton Spicer truck differentials. Spicer Corporation (now known as The Dana Corporation) manufactured these rearends for Studebaker and other three-quarter-ton trucks during the late '40s and early '50s (thus the name "three-quarter-ton quick-change"). The Spicer design consisted of two housings, known as bells, which bolted together around the center. The larger bell was deep enough to support and contain one half of the carrier, the ring gear, and the pinion gear. The smaller bell supported and contained the other half of the carrier. One axle tube and one axle were shorter than the other allowing the rearend to be centered under the truck.
Racers found that they could manufacture a centersection that would contain a through-shaft driven by the driveshaft. The through-shaft or lower shaft is supported by bearings at each end and is splined on the back end to allow a straight-cut gear to be slid on the splined end of the shaft. This gear then meshes with a gear on the splined upper shaft that drives the pinion gear. A cover, containing bearings to support the ends of the shafts and a small amount of lubricant to lubricate the gears, encases the gears. By quickly removing the eight bolts that secure the cover and changing the gears on the shafts, the final axle ratio is quickly changed.
The design of the Spicer differential simplified the conversion. Early racers were clever, "seat of the pants" designers. They designed the centersection width so that one of the smaller Spicer rearend bells could bolt to each side of the centersection. The width of the centersection and the location of the bearing races in the two smaller bells matched the distance needed to support the carrier. Two short axle tubes and two short axles completed the rearend assembly. Other than the special centersection, the entire rearend is made up of OEM three-quarter-ton truck parts: carrier, axles, ring-and-pinion gears, bearings, seals, etc.
The OEM axles are splined on the carrier end and flanged on the opposite end. The flange bolts to a hub that contains large bearings and "floats" on large tubes on the ends of the axle housings. The axle is driven by the differential, and since the axle flange bolts to the "floating" hub, it turns the hub and puts power to the ground. Since the hub is actually attached to the axle housing tube, the tire, wheel, and hub can remain attached to the differential and actually roll without an axle. This is a great safety feature for the oval track racers because a broken axle does not mean that the wheel, tire, and broken axle shaft will leave the car and cause the driver to loose control or crash.
The three-quarter-ton truck floating-hub design necessitated a wheel that followed the truck lug pattern. These wheels, known as "wide-five wheels," have five lug nut holes around a ring that is welded to the rim. The lug nut holes are out near the rim, thus the "wide-five" notation. These racing wheels resemble OEM '37 Ford wheels.
The early versions of the three-quarter-ton quick-change were fabricated and crudely machined steel pieces. The steel cover alone often weighed 10 or more pounds. However, it wasn't long before the centersections were being cast out of aluminum. Jim Frankland was one of the pioneers of this style of quick-change rearend. Jim was a racer with a shop in Ruskin, Florida. He found himself being asked to repair various three-quarter-ton quick-change rearends for area racers. Jim decided he could build a lighter, stronger, and more durable version of the rearend. Frankland Engineering was born and eventually became the largest quick-change manufacturer in the world. Jones, Kollstadt, Winters, and others followed.
Cast-aluminum bells, as well as aluminum hubs, soon followed, along with floating hubs that could mount a standard Ford wheel. As the evolution continued, we saw aluminum axle tubes, available in different lengths to allow offset for oval-track racing. Double-splined axles, with a drive plate, replaced the flanged axles. The drive plate was spline-mounted to the axle and bolted to the hub. These axles could be made any length and were made of high-strength materials that the OEM truck axles lacked.
Today, the evolution continues. You can obtain the latest technology in these rearends from Winter's Performance Products, Speedway Engineering, Frankland Racing Supply (same name, not the same company Jim Frankland started), Richmond Gear, and others. The manufacturing technology, options, durability, and weight savings have come a long way. However, the basic design has not changed since those early racers built their first three-quarter-ton quick-change rearends. As a matter of fact, we recently put a '49 Studebaker three-quarter-ton carrier (junkyard find) in a Frankland rearend in a street rod-it fit perfectly.
Jamie Frankland, the son of Jim Frankland, has a wealth of knowledge about three-quarter-ton differentials. In addition to his knowledge, Jamie manufactures and sells new and used rearend assemblies as well as rearend parts through his Frankland Welding business. He can also assemble a "locker" that will work on the street.
If you are a scrounger like us and locate one of these rearends at a swap meet, there are several things of which you need to be aware. Obviously, you need to inspect for cracks around bolt holes, in the bells, or in the housing. Inspect the area that supports the pinion gear bearing; this area is often beat up in a rearend failure. Look for burnt teeth on the ring-and-pinion gears. Keep in mind that most used three-quarter-ton quick-changes have been through the racing wars.
Another area of concern is the carrier assembly. Early racers welded up the spider gears in the carrier to produce a non-slip rearend. The welded spider gears allowed the power to be directly supplied to both rear wheels. This was good for racing but would make it nearly impossible to turn a corner in normal street driving conditions. You probably will not find one of these, but be aware they exist. After that came what was called a "locker." This rearend contained a carrier that locked up on the straightaway but allowed the axles to slip when the car negotiated the corners. Again, this was great for racing applications but does not work well on the street either, as you are not carrying enough speed or wheel spin to unlock the spider gears when you turn a corner. Today, most racing versions of this differential run a spool. A spool is a ring gear bolted to a shaft that is supported on each end in the bells-direct drive. This is also not very streetable. Luckily, today's manufacturers recognize the street rod user and have designed carriers and many other parts that make these rearends street-friendly. They also manufacture helical-cut quick-change gears. Compared to the straight-cut gears, the helical gears are much quieter. Personally, we prefer the noise-it sort of sounds like a gear drive camshaft setup-but then we are old racers who can't hear very well anyway.
If you are looking for something different, looking for something heavy duty, or just like that racing look, give the "other quick-change rearend" a try.