Well,
crap. That didn't work... ...you know what they say about when you assume...
So my rear differential is a 742 case based 3.55 sure grip. The spare junker open differential 2.76 is
also a 742 based case. What can possibly go wrong with that swap?
So I pulled the axles fist. By the way, the old Timken bearings looked good. They were perhaps a little bit dry, but rolled smoothly and with no apparent issues. Then out came the 3.55 sure grip chunk:
By the way, I have never rebuilt a rear, so I can't say I really know how to diagnose them. But I didn't see any funny wear on the teeth, and the yoke seemed tight. There didn't seem to be too much play in it either. I was kind of hoping for some "smoking gun" to present itself but no such luck.
So in went the 2.76 open diff beater chunk. I just got it in there and decided at that point to verify the yoke before I tightened it down and installed the axles.
Nope. No go. My 3.55 yoke takes a 1 1/8" U-joint. The 2.76 yoke takes a smaller 1 1/16" U-joint.
I had assumed that since both were 742 cases that the yokes, and in turn, the U-joints, would be the same. Live and learn.
Now, I know they make U-joints that can connect this to my driveshaft with 1.125" caps on one end and 1.063" caps on the other. But that is another $40, plus the work to swap out the U-joint, all for maybe 10 miles of testing?
I'm not sure what to do next. I'm not inclined to buy and swap out the U-joint too for a 1 hour test. Maybe I'm just better off trying to swap the 3.55 chunk with the 3.55 chunk in my 70? But I'd rather not tear into that car since it runs and drives perfectly...