489,741,742? are they really interchangable?

[naus360scamp]

ok so im looking for the easiest way to bump up my rearend gear and also get rid of the spool because my car is mostly a street car. Ive been looking around and i figured it would just be to swap out my whole pig (3.23 489 spooled) and replace with the same housing with the gears i wanted (355,373,391) but then i read a post on here and i noticed maybe i can not be so picky with the case and get a 741 or 742 and it would still be a simply bolt on. i did read though some of the earlier cases where different? and how can i tell the yoke size, and if everything will fit. i dont wanna buy something that wont fit. thanks matt:study:

 

[1970Duster]

Yes a 489, 742, 741 housing will bolt to any 8.75 rearend. The gears from a 489 will not fit into a 742 or 741 (and the opposite is true). The spline count on the opinion is different and the yoke size is different. Just make sure if the u joint you have now will fit.

 

[naus360scamp]

how do i measure the size? and when im buying a pig i ask is the yoke? a big? small or specific measurement?

 

[73ScampSS]

the last 3 numbers of the part number stamped on the outside of the pig (driver side) will be 741 742 or 489. I would go with the 742 unless you got some major torque output

 

[naus360scamp]

thanks 73scampss i already new that. thats not my problem. do you know about the different yokes sizes?

 

[pettybludart]

thanks 73scampss i already new that. thats not my problem. do you know about the different yokes sizes?

Most centers/yokes take the 7260 or 7260/7290 u-joints.You can just rplace your u-joints to match whichever center you find.Good luck.:burnout:

 

[naus360scamp]

hey thanks alot

 

[cudamark]

Just measure the span of your existing U-joint and get one that is the same or else you can mess around with the adaptor u-joints. The most common ones are the 7260 (2 1/8") span and the 7290 (2 5/8" span) The span on these are measured from the outside of the retainer clips on the bearing cups. There are a few other oddball pinion flanges so if in doubt, post a photo.