third member 742 case question

[resq302]

Going over our newly acquired GTX vert yesterday, I noticed that the third member has a 742 casting.  If I remember right, the metal plate which was the date coding said something like 345.  Now, since this is an early 69 car, SPO date of Oct of 68, was 742 casings still being used or would it have been a 489?  I understand anything could have happened over the 40+ years of this cars life but since it is a numbers matching car, if the third member is not correct, I'd like to change it out with one that is correctly dated and correct casting numbers.

Thanks for your input.

Brian

[burdar]

I didn't think 8 3/4's had any stamped date coding.  THey just had assembly dates stenciled onto the center section and housing.

[resq302]

Im aware of the 8 3/4 axle having a rubber stamp / stencil for the date of assembly there.  What I was mentioning about is the third member which more than likely would have been the casting date.

[moparmaniac59]

The 742 case was used in 1969. 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. Differential bearing setting (ie. backlash ) is set with threaded adjusters. The 489 case was also used in 1969, so both could be correct depending on the time frame the car was built.  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. Differential bearing setting (ie. backlash ) is set with threaded adjusters. Hope this helps!! 

                                                                      Matt B.

[Chryco Psycho]

  not that I am an expert on exact dates etc but to me I would expect the 742 to be in that car , better center section IMO as well