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.

Universal Joint Yokes
The 8-3/4″ axle was offered with two size cross & roller style universal joint. These are referred to as the ‘7260’ (2-1/8″ yoke ID) and the ‘7290’ (2-5/8″ yoke ID). Most Imperials and some C-bodies used a different universal joint. The ‘1330’ type joint was used on Imperials and others with a constant velocity joint. The 1330 uses outside snap rings instead of the inside snap rings used by the 7269 and 7290. The cap diameter for the 7260 is 1.078″. The cap diameter for the 7290 is 1.126″. The 1330 style joint cap diameter is 1.063″.
There are four different yokes that have been used with the 8-3/4″ axle for the 7260 and 7290 style universal joints. The 741/742 assemblies used a coarse spline (10 splines) drive pinion. Most of the aftermarket gears also use this coarse spline yoke mount. There is a small yoke for the 7260 and a larger one for the 7290. The 489 assembly used a fine spline (29 splines) yoke. Note: during the phase-in period of 69-71 for the 489 unit, there were several permutations of pinion size and yoke availability. 69-70 489 units may be equipped with a coarse (10) spline pinion, particularly for the 7290. There are two yokes for the 7260 and 7290 universal joints with fine (29) splines. Two additional yokes were used for the 1330 style universal joint in constant velocity applications, one for 10 splines and one for 29 splines.
Interchange Notes:
7260, 7290, 1330 yokes may be interchanged if the spline count is the same.
Note: the 9-1/4″ axle (73-up) uses the same fine spline yokes as the 8-3/4″ fine spline units (29 splines).
Strength Considerations
The 1-3/8″ 741 pinion is considered best for light-duty, non-racing applications, although it is still a capable unit in most moderate power, moderate traction street applications.
For high torque applications with high traction tires, the 1-3/4″ or 1-7/8″ should be used.
The 1-7/8″ 489 is generally considered to be the strongest. Although the stem tapers down along it’s length, it appears inherently stronger from a pinion stem perspective and the inherent strength of the fine splines (OEM gears).
The 1-3/4″ 742 has a larger rear pinion bearing yielding greater strength in this area. The 1-3/4″ shares yoke mount diameter and mounting nut with the 1-3/8″.
For perspective, the 7-1/4″ has a 1-3/8″ pinion, the 8-1/4 has a 1-5/8″ pinion, the 9-1/4″ (70s) has a 1-7/8″ pinion.
Sure Grips.
The Dana Power-Lok is inherently stronger and provides better, equal torque transmission to both axles. It’s locking capability is also proportionate to the applied torque. The Borg Warner unit is weaker, but is a more versatile unit for practical street applications in inclement traction periods. The Dana unit is the better of the stock sure grips for racing applications and has clutch rebuild kits available. An updated cone-type sure grip unit is available from Auburn Gear with 30% increased torque carrying capacity over the old version. Lockers and spools are also available from various sources.
Service Parts Information
Most replacement parts for the 8-3/4″ axle are still available. Some items not available are new Dana Power-Lok assemblies, most OEM gears, most carrier housings and complete differentials and housings. A revised version of the cone-type Sure Grips are available from Auburn Gear. The Power-Lok clutch kits are available from MP and other sources. Gear sets (typically performance oriented ratios) are available from MP and the aftermarket for the ‘489’ and ‘742’. Bearings and seals are readily available.
Selected Parts Reference
Numbers listed for reference, some may be superceded or discontinued, some variances among models/years may occur. Reference factory or replacement parts catalogs for exact replacement details.
Universal Joint Items:
Item… Chrysler… Precision… Dana… TRW
(Detroit ref.) (OEM or MP) (Moog) (Spicer) (FederalMogul)
————– ———— ——— ——– ————–
7260 joint… 4364400… 315G… 5-1306X… 20030… 20030P
7290 joint… 4057025… 316…… 5-1309X… 20059… 20059P
Combination * …………. 347 ………………….. 20226
1330 joint…. 2533202… 354…… 5-213X…. 20064… 20064P
7260 strap kit… P4120468… 318-10… 2-70-38X… 20704
7290 strap kit… P4120469… 492-10… 2-70-28X… 20705
* This is a combination of the 7260 and 7290 universal joints to allow
mating of the two styles.
3432485…  29 spline 7260 (2-1/8″ ID), also P4529481
3432487…  29 spline 7290 (2-5/8″ ID), also P4529483
3004872…  10 spline 7260 (2-1/8″ ID), also P4529480
P4529482…  10 spline 7290 (2-5/8″ ID), replaces 2808384, 3004873
2931813…  10 spline 1330, for constant velocity, ie. Imperial.
3432489…  29 spline 1330, for constant velocity, ie. Imperial.
1556556…  pinion washer, concave, 3/16″ thick, 13/16″ I.D.
2070117…  pinion washer, concave, 3/16″ thick, 15/16″ I.D.
1795175…  pinion washer, flat, 3/32″thick, 13/16″ I.D.
1795173…  pinion nut, 3/4″-16 thread, 1-1/4″ hex.
6027323…  pinion nut, 3/4″-16 thread, 1-1/8″ hex.
6028041…  pinion nut, 7/8″-14 thread, 1-1/4″ hex.
•Sure Grip Items:
Mopar Sure Grip axle additive – 4318060
Dana Power-Lock thrust block set – 2881313
Repair Kit, Dana Power-Lok – P4529484 (replaces 2070845)
Note: there is no repair kit for the Borg Warner/Auburn unit, but the internal cones have been remachined by others to successfully restore performance.
•Shim Package:
1-3/4″ pinion… P4452027
1-7/8″ pinion… P4452026
•Ring Gear Bolts:
P4529486…  71 and later (also 4131255, pkg. of 10)
P5249163…  70 and earlier
Note: the 71 and later bolts may be installed in the earlier units by drilling a shoulder relief in the attachment holes.
•Gaskets…. Seals
Position… Chrysler… National… C/R… Fel-Pro
————— ——– ——– ——– ——–
Axle inner seal… 4796698… 8695S… 15460…xxx
Axle outer seal… 2404216… 8704S… 19000…xxx
Axle flange, foam… 2070933…xxx…..xxx…. 55032
Axle flange, shim…. 2881314…xxx… see flange kit see flange kit —
Carrier gasket….. 1673367…xxx….xxx…. RDS 65833
Pinion seal, 1-7/8…. 2931862…. 5126… 18708…xxx
Pinion seal, 1-3/4…. 2931862… 7216…. 18912…xxx
Pinion seal, 1-3/8…. 2931862…8515N…18708…xxx
Yoke repair sleeve…xxx… 99187… 99187…xxx
Position… Cup/Cone… Timken… BCA… Notes:
————- ——————— ——————
Differential, side… LM 104949/LM 104912… 70-74, Borg Warner
Differential, side… 25590/25520… 57-69, Dana
Pinion, front… M88048/M88010 1-7/8″
Pinion, front… HM89443/HM89410 1-3/4″
Pinion, front… M88048/M88010 1-3/8″
Pinion, rear….. M804049/M804010 1-7/8″
Pinion, rear….. M803149/M803110 1-3/4″
Pinion, rear….. HM89446/HM89410 1-3/8″
Axle, outer….. BCA A-7… 65-74
Axle, outer….. C/R BR7…. 65-74
Axle bearing service kit: Chrysler # 3683966, one axle.
BCA differential kit: 1-7/8″, #RA-301, 1-3/4″, #RA-300
BCA axle mounting flange repair kit: Left # A-7-LK, Right # A-7-RK.
C/R axle mounting flange repair kit: Left # A7-LK, Right # A7-RK.
Vent bolt – Chrysler # 4032798
Spring mounting pads (perches) – Chrysler #P4120074
‘489’ collapsible spacer (pinion bearing pre-load) – Chrysler # 2931687
Mopar gear lubricant – 4318058
Mopar wheel bearing lubricant – 4318064
Note: the 8-3/4″ axle shaft outer bearings require packing with grease as they are not
lubricated by the gear oil.