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Information on Mopar 8 3/4 Rears

The Chrysler 8-3/4" rear axle assembly was introduced in 1957. It is a banjo-type, the differential is contained in a removable carrier assembly. The axle has an 8-3/4" diameter ring gear.  There are three basic types available distinguished by their drive pinion stem diameter. The 8-3/4" axle was the primary axle assembly used in  most car lines through 1972.

 8-3/4" Axle 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.

1-3/8" small stem pinion  (741)  Carrier casting numbers: 1820657 (1957-1964), 2070741 (1964-1972).  These numbers are found on the left side of the carrier assembly.

This assembly was typically used in low weight/low horsepower (Small Block as an example) applications through low weight/medium horsepower and high weight / low horsepower applications.  Pinion depth and bearing preload is set with shims. Differential bearing setting (i.e. backlash ) is set with threaded adjusters.

 1-3/4" large stem pinion.   (742)    Carrier casting numbers: 1634985 (1957-1964), 2070742 (1961-1969). This assembly was replaced by a 1-7/8" pinion starting in the 1969 model year. 1970 Plymouth and Dodge b Bodies 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 preload is set with shims. Differential bearing setting (i.e. backlash ) is set with threaded adjusters.

 1-7/8" tapered stem pinion.   (489)  Carrier casting numbers: 2881488, 2881489 (1969-1974).

 This assembly was introduced in 1969 and gradually replace the 1-3/4" unit through 1970  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 through high weight/high horsepower applications.   Pinion depth is set with shims, preload is set with a crush sleeve.   Differential bearing setting (backlash) is set with threaded adjusters.

All 8-3/4" carrier assemblies can be identified externally by the casting numbers. Additionally, 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 edge of the ring gear. Ratio can be determined by the number of teeth on the ring gear divided by the number of teeth on the pinion gear or by counting the ratio of the number of turns of the pinion relative to one turn of the axle shaft.

The 8-3/4" center section is removed from the front of the housing. It is retained by 10 nuts on studs in the housing. The rear of the housing is smooth, the back is welded onto the main housing.

The axle tubes are part of the overall housing. To remove the center section, remove the wheels, brake drums, and drive shaft. Chrysler Cars made pre-1965 units have a pressed-on brake hub. 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.<br>

Any 8-3/4" center section may be interchanged for another as an entire assembly.

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-Lock  Pt# 2881487). This unit utilized clutches for the differential locking action. The Power-Lock can be rebuilt using kit # 2070845 ( Mopar Performance PT # P4529484 ). In this assembly, axle drive shaft 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 cup, Chrysler numbers 1790523 and 696403).

The Dana Power-Lock 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.<br>

The differential axle bearings are:LM 104912 (Timken cone), and LM 104949 (Timken cup), (Chrysler numbers 2852729 and 2852728).

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. 

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.

 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)..

Pinions

The 1-3/8" 741 pinion is the weakest. 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 considered.

 

The 1-7/8" 489 is supposedly the strongest. Although the stem tapers down along its 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.  

The Dana Power-Lok is inherently stronger and provides better, equal torque transmission to both axles. Its 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 better for racing applications and has clutch rebuild kits available.<br>

 

Because the 8-3/4" axle was available in most body lines, there are a variety of housings available. Following are some of the passenger car axle dimensions and notations. <br>

The Perches dimension is the distance center to center between the spring mount perches.  

Body Line Track Perches Notes

 Dimensions are in inches.

A-body, 65-72   55.6   43.0    4" lug bolt circle, offered in heavy duty apps.

B-body, 62-70   59.2   44.0

B-body, 71-72   62.0   47.3

B-body, 71-72   63.4   47.3 station wagon

C-body, 64-72   63.4   47.3

D-body, 64-72   63.4   47.3

E-body, 70-74    60.7   46.0

The 8-3/4 was also available in the 58-74 D100/W100 trucks, the 64-70 A100 trucks and vans, the 67-70 A108 trucks and vans, the 71 to 74 B100/B200 vans and non-listed 57 to 64 full and mid-size car models.

 Note: the axle centerline to yoke/universal centerline is 12.35" for the 8-3/4" axle. Any 8-3/4" center section may be interchanged for another as an entire assembly.

All 8-3/4" axle shafts, 65-74, are retained by a bolt-on flange. Axles can be interchanged within housings of the same width. The passenger side axle has a threaded adjuster to set axle shaft endplay.

Note: there was a slight dimensional change in axle shaft length when the Sure Grip design changed. If interchanging axles with the slight difference, the threaded end play adjustment can be used to accommodate it..

Note: the 57-64 8-3/4 axle drive shafts were tapered and used a keyway and locknut to retain the brake assemblies and end play was set with shims. The 65 and later units use flanged axle shafts and a threaded adjuster to  set axle end play.

See Appendix A for information about the A-body 8-3/4" axle and bolt circle changes.

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. 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.

 Mopar Performance dealers, Chrysler dealers.

Moser Engineering, 1616 Franklin St, Portland IN, 47371

 (219-726-6689)

Reider Racing, 12351 Universal Dr., Taylor MI, 48180 (313-946-8672)

 

Aftermarket for general replacements, i.e. seals, bearings, etc.<br>

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.

 

Item Chrysler Precision Dana TRW

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.

 

Chrysler numbers:

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, i.e. Imperial.

3432489 - 29 spline 1330, for constant velocity, i.e. Imperial.

1556556 - pinion washer, concave, 3/16" thick, 13/16" hole diameter.

2070117 - pinion washer, concave, 3/16" thick, 15/16" hole diameter.

1795175 - pinion washer, flat, 3/32"thick, 13/16" hole diameter.

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.

Chrysler numbers:

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 re-machined by others to successfully restore performance.

.Axle inner seal 4796698 8695S 15460

Axle outer seal 2404216 8704S 19000

Axle flange, foam 2070933 see flange kit see flange kit 55032

Axle flange, shim 2881314 see flange kit see flange kit

Carrier gasket 1673367 - RDS 65833

Pinion seal, 1-7/8 2931862 5126 18708

Pinion seal, 1-3/4 2931862 7216 18912

Pinion seal, 1-3/8 2931862 8515N 18708

Yoke repair sleeve --- 99187 99187

The 65-72 A-bodies were available with the 8-3/4" axle. This was standard on all 340 equipped cars. It was also included in heavy duty packages such as 318 with manual transmission and towing options. It was often included in post 65 273 high performance manual applications.

 The bolt circle (BC) on these vehicles was 4". All other Chrysler vehicles (except some Imperials and trucks) of this era were equipped  with a 4.5" BC. It is commonly desired by A-body owners to change to the 4.5" BC when upgrading to later style disk brakes or to expand wheel choice.

 A-body 8-3/4" axle shaft swap:

There are several methods to accomplish this. Custom axles such as Strange, Summers, Moser, etc. can be specified with the larger lug pattern for the A-body housing. Longer axles from a larger vehicle may be cut and re-splined to fit the shorter A-body axle.

Donors for this operation are C-bodies, B-bodies, trucks and vans with the 8-3/4" axle and 4.5" BC.

B-body differential in the A-body  

Another alternative can be used to replace an existing 8-3/4" or the smaller 7-1/4" or 8-1/4" differential. An differential from a 66-70 B-body can be installed in the A-body (note: a 62-64 axle can be used, but it does not contain the flanged axles of the later units).<br>

The later sport coupe style cars, Duster, Demon, Dart Sport, have the roomiest fender wells. The 67-76 sedan and hardtop models have less. The 60-66 appears to be the tightest fit.<br>

The A-body has a spring perch spacing of 43.0", the 66-70 B-body is 44.0". To mount the B-body axle on the A-body springs, the perches need to be removed and new ones welded in place 1/2" inward from the original location on each side.

The B-body track width is greater than the A-body. This may be a concern depending on the wheel/tire combination. The wider track enhances handling and aesthetics to some degree. This has been performed on the authors 73 Duster, now equipped with 15x6.5" Rally wheels and P255/60R-15 tires with 11x2.5" brakes. Originally setup with 15x7" rallye wheels and P275/60R-15 tires with rolled fender lips. The larger tires exhibited scrubbing when loaded on dips / bumps.

References Manuals

Chrysler factory service manuals, various, 1964-1974, Chrysler parts catalogs, various, 1957-1974, - Hollander Interchange Manuals, Mopar Performance catalogs,

 

 

2004
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