Sounds like trouble to me. All the 8.75's are tough, but the early ones are difficult to find replacement parts for, and don't interchange with the later units. That sucks, 'cuz it would be nice to swap out the two piece design for the modern flanged axle, brakes, etc. If you want to pursue the possibilities, find out exactly which diff you have by the numbers.
Some info;
(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.
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.
There are three basic types of 8.75" carriers available, which are distinguished by their drive pinion stem diameter. The choice of axle pinion assembly was determined based on a combination of vehicle horsepower and weight. Below are the 8.75" axle carrier types.
8.75" Axle Carrier Types and Years of Production
•''741' Casting - 1 3/8" (1.375") Small Stem Pinion.
Carrier casting numbers were 1820657 (1957-1964) and 2070741 (1964-1972). This unit was usually used in low weight/medium horsepower and high weight/low horsepower applications. Although it is the weakest of the 8.75" units, it is still a stout unit, and is stronger than the Spicer-built Chrysler 8.25" rear. The 1 3/8" pinion is also larger than the pinion in the Ford 9" rear.
•''742' Casting - 1 3/4" (1.75") Large Stem Pinion.Carrier casting numbers were 1634985 (1957-1964) and 2070742 (~1961-1969). This assembly was replaced by a phase-in of the 1-7/8" pinion '489' casting starting in the 1969 model year. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. Although not generally considered to be stronger then the '489' carrier, the '742' carrier is extremely stout, and is favored by many Mopar enthusiasts because they are easier to set up. Noted Mopar enthusiast John Kunkel mentioned that the biggest advantage of the 742 carrier is that it has the largest rear pinion bearing of all the 8 3/4" carriers. The larger bearing helps to prevent pinion deflection better under a load than the others.
•'489' Casting - 1-7/8" (1.875") Tapered Stem Pinion Carrier casting numbers were 2881488 or 2881489 (1969-1974). This assembly was introduced in 1969 and was phased-in to relace the 1-3/4" pinion '742' 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, and was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. This carrier is considered to be the strongest by some Mopar enthusiasts. Because it requires a crush sleeve to set bearing preload, some Mopar enthusiasts prefer the '742' casting. This is not really an issue now because there are now parts available to eliminate the crush sleeve.
Carrier Identification:
All 8-3/4" carrier assemblies can be identified externally by the casting numbers. The casting numbers are cast onto an ID pad on the driver's side of the carrier just behind the 'snout' of the case where the yoke attaches to the pinion. In addition to the casting numbers:
•The '741' will usually have a large 'X' cast on the left side
•The '742' will usually have a large '2' cast on the left side
•The '489' will have a large '9' cast on the left side.
Hope this helps.
Dr. C
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