third member numbers

monkey said
I see a lot of third members on e-bay for sale, and the I keep seeing 3 numbers being repeated 742, 741, 489. What do these represent ? I have a 73 swinger I would like to upgrade to a 8.75 (will be relocating springs inward), are these a good deal and will they fit into any size 8.75 housing. I've seen housing with measurements of 59 1/8" and 56 1/2" end to end. whats better find a complete rear end or piece one together , Hope some of you can help steer me right

Yes the third member assembly will fit in any 8 3/4 housing. You are limited in gear choices in the 741 case so many people don't like them.

This was posted by another member.

fishy68 said
The 489 is stronger but the 741 isn't a weakling like a lot of guys think they are. You could install the sure grip unit from the 489 case into the 741 case with the 3.91 gears. That'd give you the gears and sure grip you want.

BTW: most of the strength difference between a 741 and 489 is the pinion. The 741 pinion is a much smaller o.d. but here's something to think about. What size is the o.d. of the pinion on a 741 right behind the yoke? Answer: it's exactly the same as a 742 or early 489 pinion. Only the newer fine spline 489 gearset is stronger.