Most cars have the 8 3/4" rear with 3:23 gears. Easy to spot because there are no bolt heads visible from the back as pumpkin loads in the front. Also the center section is perfectly round when viewed from the back.
The other possibility is the lowly 7 1/4" which looks very small and has 9 bolts on the cover when viewed from the back
There is a slim possibiltiy you have a Dana 60. That one has 10 bolts and looks very big when viewed from the rear. If you have this just send it to me.......
To find out if it has a suregrip, Block the front tires use a floor jack to lift the car from the center section of the rearend put the transmission in neutral and by hand turn the tire on one side and look to see if the tire on the other side turns with it. If the other wheel just sits there or turns slowly the other way no sure grip. If the other tire turns at the same speed...Jackpot!! suregrip.
To find out the gear ratio block the front tires and jack up the back. Put it in neutral. Look at the rear tire and put the valve stem at the top dead center. look under the car and make a mental note on where the U-joint is facing. While still looking at the U-joint turn the tire slowly in one direction and count how many turns the U-joint makes in a comeplete tire rotation.
If you have a suregrip then it is easy to figure out. A little less then 4 turns is a 3:90 gear, a little more then 3 turns is a 3:23, 3 and a half turns is 3:55 and so on...
If you don't have a sure grip then double the number of U-joint turns you get. 2 U-joint turns is a 3:90,
1.6 turns is 3:23, 1.75 turns is a 3:55 ect.
Most likely you have a 904 transmission in the car and if that is the case you want the one that says A999
in big letters on the top of the case. It has the most clutches and clutch discs inside.
The easy way to tell the difference between 727s and 904s in passenger cars is to measure the length
from the front of the case to the center of the yoke in back.
727-is 38 inches long
904-is 34 inches long
(Nothing wrong with the 904 transmissions, My friends and I have raced them hard on the track with very few failures. All Mopar valve bodies fit them and low gearsets are easy to get..my opinion)
