where did you see those number?
normally the ID with the gear code, day of year manufacture, posi type if equipped is all stamped (not cast ) in this location
The stamped number we are looking for is stamped on the forward facing passenger side axle tube and It'll usually be about 3 inches away from the c

The E128 is most likely
Manufactured on May 15th of a year ending in 8
GM86 on it somewhere as will that would most likely mean GM 8.6 inch with the 12 bolt cover as seen in your pictures.


The stamped number we are looking for is stamped on the forward facing passenger side axle tube and It'll usually be about 3 inches away from the carrier housing (center section of rear end housing).
Will look like this
Rear Axle Code example: CB G 112 1 E (the E here is not the same as the E above due to formatting tells us what the stamp means)

if it is somewhat modern. Since that axle is painted i am sure it is covering some numbers.

if you are not in the mood to grind your paint and find it. try a pencil rub first. or if you take a nice in focus picture with your phone of this area sometimes zooming in will show what the eye cannot see.
Otherwise its going to mean a more precise tire rotation and axle turn count to get to your number.

Once we have those first two digits we can get that ratio the last missing piece to determine what you can and cannot do with the stuff you have.

Details if this helps

this stamp can be difficult to locate on an 30+ year old axle due to layers of paint, undercoating, grease, and dirt. It may be necessary to partially strip the forward face of the passenger side axle over the middle third of the length in order to locate and discern the characters. A razor blade and/or putty knife, fine wire brush, and cleaning solution may be needed tools in this search.

Rear Axle Code example: CB G 112 1 E
(CB = Ratio, G = Plant, 112 = 112th day of year, 1 = shift, E = Positraction Source)

Assembly Plant Codes
Buick - B
Buffalo - C
Cadillac - D
Detriot Gear & Axle - G
GM of Canada - K
Warren, MI - W
Oldsmobile - O
Pontiac - P
Pontiac/Canada - M

Shift: D or 1 = Day shift| N or 2 = Night shift

Positraction Source/Code:
- = No positraction
D = Dana Positraction Differential
E = Eaton Positraction Differential
G = Chevrolet G&A Positraction Carrier
O = Oldsmobile Positraction Carrier
W = Warren/Warner Motive

Positraction Casting Numbers
Due to the possible confusion with gear ratio descriptions... a HIGHER number is a LOWER gear.
In the below examples, 2.56:1 & down = 2.41, 2.56, etc... which is actually a HIGHER gear ratio.

8.5" "Corporate"
Casting # Series Gearing
410408N 3 2.73:1 & up
410409N 2 2.56:1 & down

rear axle casting date code Rear Housing Casting Date

Example: D143 - (D = Month, 14 = Day, 1 = Last digit of year (1973)).

Month: A = Jan, B = Feb, C = Mar, D = Apr, E = May, F = Jun G = July, H = Aug, I = Sep, J = Oct, K = Nov, L = Dec

Last edited by hcb3200; 04/27/2024 10:17 PM.