I have a ten bolt posi and can't find the casting number anywhere. It measures 52 1/4 inches from backing plate to backing plate. It has flat perches for the coil springs and look the same as the type that have the plate that bolts down on the bottom coil. The casting number is 1889828. The third digit could be a six, not sure. Any help on this would be greatly appreciated.
Thanx,
Dennis

Casting Numbers:

10-Bolt Housing:
1964 Chevelle 3839390N
1965 Chevelle 3959139N
1966 Chevelle 3875744N
1967 Chevelle 3894938NF
1968 Chevelle 3917123NF
1969 Chevelle 3859037NF
1970-72 Chevelle 3969277N

Look on the front of the passenger side axle tube for ID code.
http://www.novaresource.org/images/rearcodeloc.gif

The code doesn't look right it should have some letters in it. Your axle code should be on the drivers side tube about 4-5 inches from the center on the top. I believe yearone's web site has an axle decoder. hope this will help.

This came with a parts lot along with alot of pontiac items as well. I will check for the code tomorrow. The axle housings have light pitting in them, and have been repainted within the last ten years so don't know that i can recover the code.
Dennis

Okay, code is not visible, but the measurement from BP to BP is 52 1/4". Perhaps an s-10?

Doubt it's from an S-10 as they have leaf springs.
You might want to dig through the paint for the code as any other way will just be a 'might be a' type answer.
http://www.coloradok5.com/axleguide.shtml
http://www.jdrace.com/ (look through the Diff ID pages)
http://carnut.com/specs/frear.html
http://50chevy.freeservers.com/Suspension_Widths.html