Here Are The Numbers From The Axle Tube (cw0606b)
The Housing Numbers (3917124NF) Can Anyone Help?

I'm showing 3:31 open .

3917124NF is a 1968 model year casting number. A few early ones (May casting dates) have been found with the narrower 1967 width. The 0606 indicates June 6 assembly date. If the housing was cast in May/June 1967 then this might be a very late narrow 67 model or a very early 1968 model, but if the casting date is later, or 1968, then it would be the wider 1968 model. What is the casting date on the rear of the center section (lower driver side web) and have you measured the width? As indicated in the post above, CW is a 3.31 open differential for either year.

Bruce

tHE CASTING NUMBER IS 67890 AND THE WIDTH DRUM TO DRUM IS 54 INCHES. WHAT DOES OPEN MEAN? I KNOW THE CAR HAS A 4.88 GEAR WITH POSI NOW.

I have seen the 67890 and 12345 refered to as test marks, and are found on different years of 10 bolts and 12 bolts. The 3917124 number is what is referred to as the casting number, and is unique to the 1968 casting. 1969 used 3959038 and most 67s used 3894939. These are 12 bolt casting numbers; 10 bolts were different. I don't know how you are measuring the width to come up with the 54 inches measurement. 64 to 67 housing measure 60 inches outside of drum to drum, and 68 to 72 housings are 1 inch wider overall. I measured 54 1/2, backing plate flange to flange on my 66 housing. A 68 to 72 should measure an inch wider.

Bruce

Open= Non-posi