High Pinion Axle - Straight Axle Dictionary

Straight Axle Dictionary Cast Axle Housing

Here we see the inside of a Dana rear axle that uses a cast centersection to house the differential. Pinion gear setup and gear backlash are adjusted while working in the axlehousing.

Here we see the inside of a Dana rear axle that uses a cast centersection to house the dif

Cast Center Housing vs. Third Member
There are two types of differential housings used in straight axles. A cast center housing holds the differential carrier bearing caps and uses a bolt-on inspection cover. This is common on many domestic axles. All ring-and-pinion setup must be performed at the axlehousing, which means it often is performed under the vehicle. Examples of axles with cast centersections include Dana 30, Dana 44, Dana 60, and GM 10-, 12-, and 14-bolt axles.

An alternative method of mounting a differential carrier is in what is called a drop-out centersection, or third member. This type of axle is common on many imports and on the venerable Ford 9-inch housing. In this case, the carrier is mounted in a cast housing that bolts up to a flanged hole in the axlehousing. These are also known as banjo-style axlehousings.

Straight Axle Dictionary Toyota Axle Housing

Toyota axlehousings typically use a drop-out design where a third member bolts to a studded flange on the face of the axlehousing. Once the third member is installed, the axleshafts are slid in to mate with the splines in the differential carrier.

Toyota axlehousings typically use a drop-out design where a third member bolts to a studde

One disadvantage to a third member axle is that there is typically no easily removed inspection cover. The entire third member must be removed to view or setup gears, and this requires removal of the axleshaft ends from the differential. However, once removed, the third member can be carried over to a workbench where all gear work can be performed. Gear setup is more convenient with this method. Trail swapping a broken third member is also a realistic option.

Low-Pinion vs. High-Pinion
Most often, a straight axle will have what is referred to as a low-pinion design, meaning the pinion gear meshes with the ring gear below the centerline of the axle. High-pinion designs are ones where the pinion gear meshes above the centerline of the axle.

The big advantage of running a high-pinion axle is that it keeps the driveshaft higher, improving ground clearance. This is especially helpful where tall lifts or short driveshafts are in use, and it provides lower driveshaft angle when compared to using a low-pinion axle. However, moving the pinion flange or yoke upward on the axle means that there may be more clearance issues with other vehicle parts during full up-travel.

When used in a front axle application a high-pinion axle and gearset is generally 20 to 30 percent stronger than its low-pinion counterpart. However, when used as a rear axle, a low-pinion axle and gearset is 20 to 30 percent stronger than the high-pinion version of the same axle.

This is a typical low-pinion version Toyota third member that could fit in the axlehousing shown on the previous page. It does not use a removable inspection cover and contains all the moving differential components in this center chunk that drops into the center of the axlehousing. High- or low-pinion configurations are independent of whether the axle uses a cast centersection or third member.
This is a typical low-pinion version Toyota third member that could fit in the axlehousing
With a cast centersection, such as that found on many domestic axles, gear work must be done under the truck, unless the entire axle is removed from the vehicle. The carrier bearing saddles reside in the housing, so the differential and bearings are installed and bolted into the centersection.
With a cast centersection, such as that found on many domestic axles, gear work must be do
A custom-built high-pinion front Ford 9-inch such as this can offer about 4-5 inches of additional driveshaft ground clearance and reduce driveshaft angle. However, clearance between the higher driveshaft and components above it may become an issue under full suspension compression.
A custom-built high-pinion front Ford 9-inch such as this can offer about 4-5 inches of ad

This type of unit bearing assembly can be found on a number of late model trucks. The four-bolt flange in the foreground bolts to the outer knuckle of a Dana 60 front axle. Behind it you can see the eight-hole wheel hub where the brake rotor sits. This is a sealed spindle, bearing, and wheel hub unit.

This type of unit bearing assembly can be found on a number of late model trucks. The four

Fixed Spindle vs. Unit Bearing
On a front axle, you’ll encounter two types of bearing assemblies: fixed spindle and unit bearing. For many years, 4x4 axles used a hollow fixed spindle on which a wheel hub spun on tapered roller bearings. In recent years, more OEM manufacturers have started to shift to the use of unit bearing assemblies. On these, a bearing set and spindle reside in a sealed, non-serviceable assembly that is bolted to the axle as a unit.

With a fixed spindle design, the wheel hub slides over a spindle and rides on a set of tapered roller bearings. The assembly does require proper adjustment of the bearing preload, whereas a unit bearing assembly simply bolts onto the axle. However, this is an easy task and the design allows for bearing maintenance and replacement. FW

With a fixed spindle design, the wheel hub slides over a spindle and rides on a set of tap

Traditional fixed spindle assemblies offer the ability to clean, repack, and replace individual components as needed. They are also typically a stronger unit than a comparable unit bearing assembly. For some applications, there are aftermarket kits to convert from the use of a unit bearing to a fixed spindle for longer wear life and the ability to perform maintenance.