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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,
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