It's an 8 3/4. The axles are A body length if I measured them correctly. I'm a little perplexed as I've had the car for 2 years and never thought for a second that the diff was a little narrow. The springs mounts all look stock so it seems impossible that the diff could be narrowed. The only other possibility is that Yukon supplied extra long axles/measured them wrong. They were supposed to be 30" long. I assumed that they were measured from the front of the bearing to the end of the axle. I'll have to get some more measurements now that it's not on axle stands after getting new 3.55's, bearings, Dyna-Lok, bearings, axles, etc.