1961 f100 rear differential identification help

[chisum5013]

Can someone help me identify the type and specs on this tag that was on the rear end of a 1961 f100 with a 223 six cylinder engine. Please see attached photo Also, what kind of fluid do I use in it? Thanks for your help in advance.

[ultraranger]

Can someone help me identify the type and specs on this tag that was on the rear end of a 1961 f100 with a 223 six cylinder engine. Please see attached photo Also, what kind of fluid do I use in it? Thanks for your help in advance.

9-inch rear end, open (single track) differential, 3.70:1 ratio.

The rear end will require 5 pints of gear oil (85W-90 weight). This will be 2-1/2 bottles worth but, you will have to get (3) 32oz bottles of gear oil to fill the rear end.

[chisum5013]

Thanks for your help, how did you tell its a single track?

[ultraranger]

If you look at the second line of the tag, it reads; "3.70." If the differential was not 'open,' there would be an "L" where the dot is, between the "3" and the "7". --Example: 3L70.

The 9-inch rear came out in 1957. Most Fords (cars or trucks) have open differentials but 'locking differentials were available/optional from the beginning. In the very early Fords, the locking differential was known as the Equalok. I'm not certain exactly when it changed but sometime in the '60s, Ford began using the Limited-Slip differential.

I haven't been able to find any physical difference between an Equalok vs. the Limited-Slip differential. I suspect it was just a name change and not a completely different differential. Whenever the Limited-Slip (or at least the name) took over, that differential was produced through the 1968 model year.

In 1969, Ford actually redesigned the differential, dropped the (weaker) Limited-Slip differential and went to the much improved Traction-Lok differential. However, the '69 Traction-Lok differential is the worst year of this differential to have, due to (4) large holes in the drivers side casting of the diff. In 1970 ('70-'85), the differential casting was redesigned to eliminate the holes. --the holes in the '69 casting weakened the left side of the diff and was prone to cracking/breaking in this area, near the carrier side bearing.

[chisum5013]

Thanks for all your help!!!!!