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Chrysler 8 3/4” Axle Guide - Adapted from the Mopar Mailing List

The following conglomeration of information should help a person be able to locate, identify, and install an 8 3/4” Chrysler rear axle in their AMC product.  Many topics are covered, and the text is compiled into one long document in order to speed locating the information you need.  The topics covered are as follows:
    General
    Where to Find One
    Axles and Housings
    Center Section Types
    Sure Grip
    Universal Joint Yokes
    Strength Considerations
    Service Parts Information
    Selected Parts Reference
    Appendix A:  8-3/4 A-body axle upgrade to 4.5" bolt circle
    Appendix B:  How to Put One in a Javelin (or other AMC)
 

General

The Chrysler 8-3/4" rear axle assembly was introduced in 1957.  It is a banjo-type (Hotchkiss) axle, ie. the differential is contained in a removable carrier assembly which is extracted from the axle housing toward the front of the car.  It is retained by 10 nuts on studs in the housing.  The differential “cover” (although permanent) as viewed from the back of the car is smooth and hemispherical; it is welded onto the main housing.  The axle tubes are part of the overall housing.  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 Chrysler car lines through 1972.
 

Where To Find One

The first thing one needs to know in order to find the right axle for the job is the Chrysler platform code system.  With an understanding of the different vehicles involved, you can then determine which one will best suit your application.

A-body models include:
1964-76 Plymouth Valiant, 1964-69 Plymouth Barracuda, 1970-76 Plymouth Duster, 1972-76 Plymouth Scamp, 1964-76 Dodge Dart, 1971-72 Dodge Demon, 1973-76 Dodge Dart Sport, 1969-76 Dodge Dart Swinger

B-body models include:
1965-70 Plymouth Belvedere, 1965-74 Plymouth Satellite, 1968-74 Plymouth Road Runner, 1970 Plymouth Superbird, 1967-71 Plymouth GTX, 1965-74 Dodge Coronet, 1968-71 Dodge SuperBee, 1966-74 Dodge Charger, 1969 Dodge Charger Daytona

C-body models include:
All 1965-74 full-size Chrysler models (Newport, New Yorker, Imperial), 1965-74 full size Dodge and Plymouth models (Polara, Monaco, Fury, Sport Fury, etc.)

E-body models:
1970-1974 Plymouth Barracuda and 1970-1974 Dodge Challenger
 

Axles and Housings

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.  The 'Perches' dimension is the distance center to center between the spring mount perches.  Dimensions are in inches.

  Body line      Track       Perches                Notes
-------------  ----------  -----------     -----------------------
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 (and variants), the 64-70 A-100 trucks and vans, the 67-70 A-108 trucks and vans, the 71-74 B100/B200 vans and non-listed 57-64 full and mid-size car models.

Notes:
1) The axle centerline to yoke/universal centerline is 12.35" for the 8-3/4" axle.
2) Any 8-3/4" center section may be interchanged for another as an entire assembly.
3) 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 end play.
4) 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 accomodate it.
5)  The 57-64 8-3/4 axle driveshafts 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.
6)  See Appendix A for information about the A-body 8-3/4" axle and bolt circle changes.
 

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 preload 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 preload 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 relace 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 may 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.  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 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.

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 univer- sal 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

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 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.

Some sources
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, ie. seals, bearings, etc.
 

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.

Yokes
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" 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.

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             ---
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             ---

Bearings
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 preload) - 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.
 

Appendix A:  8-3/4 A-body axle upgrade to 4.5" bolt circle

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 resplined to fit the shorter A-body axle.  Donors for this operation are C-bodies, D-bodies, trucks and vans with the 8-3/4" axle and 4.5" BC.  Moser Engineering can perform the cut and respline operation.  When selecting a donor axle shaft, look for one that does not taper along its length.  Note: A-body 8-3/4" axles were equipped with 10x1-3/4" drum brakes.  Replace these with 10x2-1/2" or 11-2-1/2" brakes and associated hardware from the donor vehicle or similar.
 

Appendix B:  How to Put One in a Javelin (Or Other AMC)

AMC’s use a 43 1/2” perch to perch spacing for all models from 1964-78, and possibly even further.  Narrow body cars (68-70 Javelin & AMX, Gremlin, Hornet, etc.) use a 57” track width, and wide body cars (71-74 Javelin, Rebel, Matador, etc.) use a 60” track width.  Comparing these numbers to the table above, it would appear that all of our axle needs can be fulfilled with either A-body or B-body axles, depending on which AMC vehicle we own.  The 1969 A-body axle that I installed in my 1969 Javelin measured 57 1/4” from drum face to drum face, although the listed track width is 55.6”.

The spring perches don’t need to be moved in order to install the axle.  Most leaf springs will allow 1/4” of side movement to permit the installation easily.  You can purchase new Mopar Performance spring perches from Jeg's for $11.69 a pair if you feel the need to relocate them.

You can use the stock AMC shocks, but you need the shock/spring mounting plates from the donor Mopar.  Use the passenger side plate on your drivers side and vice versa (Chrysler mounts the shock on the outside of the leaf spring, AMC mounts it on the inside).  Another mounting option is to use Lakewood's "Traction...Action" bars, which are a combination shock/spring mount and traction bar.  Buy some u-bolts for a 69 Cuda and bolt the axle in.

The driveshaft and u-joint require no modification typically.  Moroso makes a fine u-joint girdle set to replace the stock straps for about $22.

Brake lines will have to be modified to fit each application.  On the rear end I used the distribution block was located on the drivers side.  I relocated it to the passenger side and made new lines.
 

References

- Chrysler factory service manuals, various, 1964-1974
- Chrysler parts catalogs, various, 1957-1974 - Hollander Interchange Manuals, 40th
  edition
- Mopar Performance catalogs
- Mopar Performance Chassis Manual
- Mopar Performance Oval Track Manual
- Mopar Action magazine, selected articles
- High Performance Mopar magazine, selected articles
- Chrysler Car Enthusiast, Engines, Etc magazine, selected articles
- BCA/National catalog # 510-1, 1995
- CR Seals & Bearings catalog # 457205, 1991
- American Bearing catalog # 710, 1980
- Fel-Pro Master Gasket Catalog, # 900-96, 1/1996
- Precision Universal Joint catalog # MC-86, 1/1986
- TRW Universal Joints catalog # X-4003, 1995
- Mopar Mailing List (MML) postings