Rear Differential with out tag, HELP

[jbird7262]

HELP !!, I have a 99' 4x4 XLT 4.0, needs a rear diff, found 2, both are 373, 8.8 with 10inch drums, the rear in my truck is S359S and one donor rear is a 98' S354M which is 373, 8.8, 10inch brakes but (NL) posi, mine is limited slip (L). The other rear is missing the tag but came from the same year/engine 99' . All are 28 spline axles. Is there a way to find correct ratios and limited or posi from the inside numbers after dropping the cover? The guy with the rears says he's pretty sure that the one with out the tag is the correct one for my truck. I can get the frt diff transfer case and rear diff from the tagged rear end for $250, the other rear $150, any tips on decoding with out the tag? There are no vehicals just spare parts so no vin#

 

[chefduane]

If you can get a VIN then you can find a Built Sheet online from compnine.com that tells you everything about the build for that vehicle. It's $5 for 5 vehicles.

 

[swshawaii]

Check the AXLE code on the bottom of the VIN sticker on your drivers door pillar.
http://www.explorerforum.com/ntrprize/Axle.htm

Click Vehicle, enter VIN, and click Minor features.
https://www.etis.ford.com/vehicleRegSelector.do

 

[jbird7262]

There are no vehicals, just extra parts, wish it were that simple, Thanks

 

[imp]

Ya wanna know 2 things, right? Ratio, and whether limited-slip. Both are staring at you if you yank off the back cover plate.

If limited-slip, you'll see a S-shaped spring within the differential carrier. Shine a light in there, support ends have a helper if necessary, turn the pinion gear. Count the number of teeth on both the pinion (little one way in the front) and the ring gear. Divide the ring gear number of teeth into the pinion number of teeth, and ya got the ratio.

It can be done by counting number of drum turns vs. driveshaft yoke, but tricky if not limited slip, or bad limited slip. Actual counting of teeth surest way. imp