Is this rear end a 8.25 or 9.25? Also is it a sureprip [posi]? The guy says its a 9.25 and has 3.55 gears and is a suregrip out of a truck. I don't know a whole lot about these rears I need it for my 84 D100. Thanks

10 bolt = 8 1/4

12 bolt = 9 1/4

gear stamp shows 3.55

yes that is a 9 1/4 limited slip

if I see it correctly looks like early 84' for the yr on ring gear stamp also

Thanks! So that should bolt right into my 84 D100 correct?

Check to make sure the bolt pattern where the wheels mount is the one you want. The trucks used at least two different patters depending on the year and application. (2 or 4 wheel drive)

I believe there were some 1984 trucks built with both the small and large bolt patterns.

If you want to switch bolt patterns, you can do so fairly easily on the two wheel drive trucks. I believe all that is required to change the front is to buy rotors with the correct pattern.

It is also possible to switch axle shafts in the rear axle to switch patterns. I haven't done this, but know it can be done.

yes to swap axle from large to small you need the correct axles with the matching c-clips IIRC.

84 should be the 5 on 4.5 85 was the change.

spring pads should be 43" centers and bolt right in the truck.

if you are replacing a 10 bolt, it is smaller and may need a drive shaft correction.

9 1/4 to 9 1/4 is bolt in.

Learn some more, Scratchhopper!

The 8 1/4 and 9 1/4 use the same length driveshaft. They have the same dimension from axle centerline to front of the input flange. 8 3/4 and Dana are different. Information from my old Direct Connection Chassis book.

R.

PS: The limited slip you have is the cone-type. You'll want to clean the housing carefully as it may have metal particles from the cone wearing into the case. I'd use a full synthetic 75W or 85W-140 gear oil with a bottle of limited slip friction modifier, I hear the one from your friendly ford dealer is a good choice.