[QUOTE=El_Beautor;672021]The front diff itself is exactly the same whether you have a ZR2 or non-ZR2. ( Dimension wise ) The ZR2's & standard trans 4x4 came with a cast iron case and ZR2's also had hardened gears ( 3:73 ) and CV axles, stock blazers came with an aluminum case.

 

I agree that ZR2s came standard with 3.73 gears, however the only s-series trucks (ZR2 and non-ZR2) that came from factory with an iron front diff were manual transmission vehicles, and even then not all of them did. All automatic transmission ZR2s came with the aluminum front differential housing. As far as I know, GM never published a separate part number or RPO for the iron front differential. There's a lot of research that was done over on the ZR2USA forum trying to pin down all the details.

 

Just to add to the mystery of iron front diffs,some AWD Astro vans and some Bravadas also had them. ( with one piece right axle tubes ) It looks like think the S10 had to be the V6 standard shift to be fitted with the iron differential.