Yet another differential question.....

[HemiOrange70]

I checked under my car and the housing states it is a 8.75 489. Can the gears inside be non 489, ie a 489 housing with  741's? Because I have the 2 1/8 pinion yoke and 489's never came with the small one. Also i rotated the wheel once and the pinion only went around 1 1/2 complete turns-what does this tell me?? Over my head on diffs

[chrisII]

 ive got a 489 case with the small yoke, think ive got a couple of them in fact. dana 60s even came with the small joint in trucks in some years. ive honestly never understood why in some years different cars came with big or small joints. might have ben high perf models or something like that. if you have a 489 case it has to have gears for a 489. i guess it would be possible to put spacers on the smaller pinion.. but it makes no sence being the 489 is the most comin case and seems to have the most gears avalible.
 
   checking gearing on an open can be confusing. your gear ratio is how many turns it takes of the pinion to spin the wheel one turn. in order to do this in an open diff you have to have one wheel stoped (on the ground) and spin the other. on a locked or posi they shuld turn together.

[matt63]

My '73 Cuda has the 489 case with the smaller 7260 yoke.  Perhaps the larger 7290? yoke only came with BB cars.

[Alaskan_TA]

Lots of 489 cases came with the small yoke. 

Barry

[HemiOrange70]

Well I am happy because I originally thought I had a 7 1/4 rear and know a 489.....too bad it isn't a sure grip, but I don't want to get greedy. That will come...thanks

[moper]

Also, turning the driveshaft and counting doesnt work with open diffs. The spider gears change the effective ratio. You need to turn both rear wheels at the same time in the same direction, and count the revolutions of the yoke/driveshaft. If it's original, there will be a small aluminum tag at about the 10 or 2 O'clock position with the ratio stamped into it. If the diff was ever removed, it's probably gone by now.