"The guy's not sure what it has though, any info I can provide him to help determine it?"
Is the confusion on which rearend or the gear ratio? I'm assuming the 71 is a GM product. If so it Should be an Eaton HO52 or HO72, in which case the differential is an easy bolt in deal on your truck. Lots of photos online to help identify.
If the question concerns gear ratio, then: If lucky you May find a tag on a cover bolt, or you May find a stamped set of numbers on the top of the axle housing just to the right of the differential. Since they're hand stamped they will likely be shallow, dim and covered with rust and or grease. Short of finding a tag the easy way if the rearend is still in the truck is raise the truck so both rear wheels turn. With the tranny in neutral turn one wheel, if the other turns in the SAME direction, it has a locker or limited slip rear. In that case mark the drive shaft (ds) and tire, turn a wheel one complete revolution while counting the ds rotations. A very little past four ds rotations is a 4.10 gear, a little past 4 and a half turns is a 4.56 or 4.57.
When one wheel is turned and the other goes in the opposite direction, then it's an open or non limited slip gear set. In that case you need to turn the marked wheel 2 complete turns and count ds rotations. Or, turn one time and multiply the ds rotations by two in order to determine final drive ratio.
You can always pull the differential cover then count and divide the ring gear tooth count by the number of pinion teeth.
Last edited by moparguy; 07/11/2017 3:01 PM.
