How do you measure a ring gear, as in 7.5 or 8.8 inches? Is the measurement the base diameter of the gear or is it the outter diameter of the teeth?

 

i think it is the outer diameter

 

So it would be the red measurement?

 

If it is the red mesurement that means I have an 8.8 inch rear end. How ever I just replaced my outter axle bearings and ordered some from rock auto. The 8.8" wheel bearings from rock auto were too big to fit, so thinking that roch auto screwed up, I went to get some at auto zone. Auto zone had 8.8" wheel bearings but they were the same size as the rock auto ones. Instead, the 7.5" wheel bearing from auto zone was the right size. So apparently I have a 7.5" axle with an 8.5" ring gear. What is wrong here?

 

you have an 8.8. im pretty sure 28 spl 8.8s and 28spl 7.5s have the same bearings. im not sure though. they probably gave you 31 spl bearings the first time

not certain on this. either a 31spl 8.8 or a 7.5 use the larger bearings. the 28 spl 8.8 i know uses the smaller bearings

 

That's what I thought. I just found it odd to get the wrong size bearing from two sources even though I gave them the correct information, 1998 4x4 4.0 ect.

 

post a pic up of your rear axle with the cover on, i can tell you what it is. the 7/5 is "flatter" on the topand bottom of the case

 

You mean the axle shaft bearings? If so, 28 spline 8.8 and 7.5s share the same bearing....even the shafts are the same between the two. 31 spline 8.8s have the larger shaft bearings.

 

yes the 28spl shafts are the same but i think the O.D. of the bearing is different

 

I checked out the comparason pictures and it definitely is an 8.8" as the axle tag confirms...
So RockAuto and AutoZone's catalog thing is screwed up. It was the bearings closest to the drums that I replaced, the wrong ones seemed to have the right inner diameter but the outter diameter was was at leat a 1/4 inch too big.