Dropouts & Pinion Supports
History and Design
While only big trucks and imports still use removable carriers they were the norm into the 1960’s. This design consists of a cast or welded housing which carries the weight of the vehicle and axle bearings. The drive gears and differential are held by a removable cast-iron carrier. Due to the shape, dropout axles were often referred to as "Banjos".
Advantages, Disadvantages, and Upgrades
The biggest advantage of a dropout is that the differential can be removed for easy service on the bench. In addition vehicle dynamics that cause the housing to flex will not affect differential operation as much as they do with an integral carrier.
The biggest reason for the decline in removable carriers is the cost. Compared to an integral carrier type the removable carrier is more expensive to manufacture as well as being heavier than its equivalent.
If you have an OEM removable carrier there are options if you’d like to give it more strength or power, options like:
- • Nodular iron or aluminum materials which offer a significant strength increase over cast iron
- • Larger cap bolts to stand up to higher torque
- • Load-bolts to decrease ring gear deflections under high torque situations
- • Larger carrier bearing bores to accommodate larger aftermarket axle upgrades.
Featured in arguably the most popular of all dropouts on the market, the Ford 9" dropout, pinion supports unbolt from the front of the dropout and hold the pinion in place. If you have a high power application you’ll want to replace the stock pinion support, which is made from cast iron and can flex, with a heavy-duty aftermarket pinion support made from stronger materials such as nodular iron and 6061 aluminum. Many aftermarket supports also feature larger pinion bearings to decrease pinion deflection, or accommodate larger pinion splines on aftermarket gears.