8-3/4 details

Center Section Types
The 8-3/4″ axle was available in three basic types. The types are differentiated by the pinion stem diameter….1-3/8″, 1-3/4″, 1-7/8″. The choice of axle pinion assembly was determined based on the application. Differential bearing setting (ie. backlash ) is set with threaded adjusters on all carriers. All 8-3/4″ carrier assemblies can be identified externally by the casting numbers.
•1-3/8″ small stem pinion (aka. ‘741’)
Carrier casting numbers: 1820657 (1957-1964), 2070741 (1964-1972).
This assembly was typically used in low weight/low horsepower applications through low weight/medium horsepower and high weight/low horsepower applications.
Pinion depth and bearing pre-load is set with shims.

•1-3/4″ large stem pinion (aka. ‘742’)
Carrier casting numbers: 1634985 (1957-1964), 2070742 (~1961-1969).
This assembly was replaced by a phase-in of the 1-7/8″ pinion starting in the 1969 model year. 1970 RW (Plymouth and Dodge mid-size) were the last models to use the 1-3/4″ which appeared in a 2881489 case. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications.
Pinion depth and bearing pre-load is set with shims.

•1-7/8″ tapered stem pinion (aka. ‘489’)
Carrier casting numbers: 2881488, 2881489 (1969-1974).
This assembly was introduced in 1969 and was phased-in to replace the 1-3/4″ unit through 1970. Note: the 1-3/4″ pinion also appeared in some 489 carriers during this period. By 1973, the 489 was the only unit available in passenger car applications. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications.
Pinion depth is set with shims, preload is set with a crush sleeve.

The 741 commonly has a large X cast on the left side, the 742 may have a large 2 cast on the left side, and the 489 has a large 9 cast on the left side. Through 1965, the factory ratio was stamped on the identification boss, followed by an ‘S’ if Sure Grip equipped. After 1965, a tag was affixed under one of the carrier mounting nuts to identify the ratio. If Sure Grip equipped, an additional Sure Grip lube tag was sometimes affixed; later years sometimes had the filler plug painted orange.
Gear ratios available on the 8-3/4″ axle through the years include: 2.76, 2.93, 3.23, 3.31, 3.55, 3.73, 3.91, 4.10, 4.56, 4.89, 5.17, 5.57. On OEM gear sets, the ratio is usually stamped on the ring gear edge. Ratio is determined by dividing the number of teeth on the ring gear by the number of teeth on the pinion gear.

The 8-3/4″ center section is removed from the front of the housing. To remove the center section, remove the wheels, brake drums, and drive shaft (note: pre- 65 units have a pressed-on brake hub…requires a puller for removal). Remove the axle shafts, 5 bolts on the backing plate flange on post 64 units, use puller for pressed-in pre-65 units. Remove the 10 nuts on the housing studs around the carrier perimeter. Remove the carrier…may require prying, fluid will drain when carrier gasket seal is broken.

Sure Grip
Sure Grip is the Chrysler name for a limited slip differential. It was optional on the 8-3/4″ axles, 1958-1974.
Two styles were used:
•1958-1969 used the Dana Power-Lok (# 2881487). This unit utilized clutches for the differential locking action. The Power-Lok can be rebuilt using kit # 2070845 ( Mopar Performance [MP] # P4529484 ). In this assembly, axle driveshaft end thrust is taken by the thrust block assembly (replacement # 2881313). This Sure Grip appeared in the 741 and 742 assemblies. The axle bearings are: 25590 (Timken cone), and 25520 (Timken cup), (Chrysler numbers 1790523 and 696403). The Dana Power-Lok can be recognized by its bolt-together assembly, bolts around the side opposite the ring gear, and multiple openings exposing the cross shafts.
•1969-1974 used the Borg Warner Spin Resistant (# 2881343). This unit utilized a spring-preloaded cone friction arrangement for the locking action. Axle end thrust is taken by the cross shaft. This Sure Grip appeared in ‘489’ assemblies and 70 and later 741/742 assemblies. The differential axle bearings are: LM 104912 (Timken cone), and LM 104949 (Timken cup), (Chrysler numbers 2852729 and 285272. The Borg Warner Spin Resistant unit can be recognized by its lack of bolts on the side opposite the ring gear (like the Dana), and two openings exposing the preload springs. Borg Warner sold this design to Auburn Gear who currently offers the replacement Sure Grip assemblies.
Non-Sure Grip differentials can be identified by the large openings in the differential exposing the differential (aka. spider) gears. There are no springs or clutches.
Interchange Notes:
The two Sure Grip types can be interchanged between the carriers if the matching differential axle bearings are retained. The outside diameter of the cups are the same between the 741/742 and the 489; the inner cone differs. The Sure Grip differential can be used as a direct replacement for the non-Sure Grip within the carrier/bearing limits previously noted.