Chrysler 8 3/4” Axle Guide
Don't remember where I found this one. Maybe at
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
Handy Dandy ID Picture
(click to enlarge!)
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:
B-body models include:
C-body models include:
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
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.
Handy Dandy Picture For Reference
(click to enlarge!)
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')
1-3/4" large stem pinion (aka. '742')
1-7/8" tapered stem pinion (aka. '489')
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 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.
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.
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
* This is a combination of the 7260 and 7290 universal joints to allow
Sure Grip Items
Ring Gear Bolts
Note: the 71 and later bolts may be installed in the earlier units by drilling a shoulder relief in the attachment holes.
Axle bearing service kit: Chrysler # 3683966, one axle.
Note: the 8-3/4" axle shaft outer bearings require packing with grease as
they are not lubricated by the gear oil.