I have the diff out of my '71 and am trying to determine what ratio it is. What #'s am I looking for and where would they be? Anyone know

lognhorn, go to the general discussion forum and look for the post matching numbers. the last answer by adam's apple tells you where to find it.

 I looked and there are no numbers on the bottom at all. There are some on the sides, but I don't know what they mean. There is one that is 399143. On the other side is an F 5 1.

Count the number of teeth on the ring gear. Should be around 40.

 Thanks Dave. It probably would help if I had it apart. I'm saving that for Joel.   I was just trying to find the #'s  on the outside that would tell what ratio is was.  'preciate the info tho.

When you said you had it out I assumed you had the cover off. My bad.

 Had fun getting it out tho. I thought the cross member it bolts to in the rear would come off when you removed the bolts from the ends. If it does, it must be really stuck (rusted) on. Had to drop the left muffler and center hangers to get it out.

If you can just turn it and count the rotations of the shafts it will give you a good idea.  If the slower one goes around once and the quicker one turns approx. 3 1/2 times you have a 3.55.  If approx. 3 3/4 time then it would be 3.73.  Crude but you can get an idea. 

Without opening up the rear just jack the car up,mark the tire and driveshaft at one spot. Put the trans in neutral then rotate the tire one full turn. Count the rotations of the driveshaft. Same as 71shark stated. 3 1/2 turns =3.55, 3 3/4= 3.73. Just convert the rotations into decimal and you will get your ratio. Some ratios are 3.08,3.23 3.36,3.55,3.73,3.90,4.11. You can have ratios higher or lower but these are some of the general ratios.

If you already have it out, you probably already have the car jacked up!!!!

Dave
(in a smartass mood)