ID 8 3/4 gear ratio

[alphabuck]

im trying to figure out exactly what my rear end is.  it seems theres a couple of different 8 3/4 rear ends? id like to know what i have and what ratio is inside? where should i look for identification?

[hemiken]

  Stick your head under the driver side of the car and you will see a sequence of numbers on the third member or chunk, the section that unbolts from the housing.  Record the numbers and report back here.  It will have either 741 or 742 or 489 as the last three digits on the center that are your reference numbers from now on.

[Chryco Psycho]

For the gear ratio you need to jack up the car & rotate the Yolk & count the 3 of rotations of the tires , the tire MUST both turn equally to be accurate , if you have an open diff leave one tire touching the ground so it will not move & count the # of rotations to get the trie to rotate 2 full rotations 

[alphabuck]

dunno if its good or bad but its a 741 thanks for the help

[Katfish]

http://www.mymopar.com/Mopar8_75RearEndGuide.htm

[hemiken]

  Alphabuck a 741 case is good........................

But the 489 case is better and the 742 case is better than that, the good thing is it is an 8 3/4 and you already have it in the car.

[Chryco Psycho]

 

[JeffAARy]

I recently checked my ratio.  I jacked up the car and put a mark on the tire and driveshaft.  Since I couldn't watch both at the same time, I decided to just watch the driveshaft since I was spinning the tire by hand and I knew where my hand was.  I spun the tire and counted the revolutions of both the tire and the driveshaft.  To rotate the driveshaft 20 times (the more revolutions you make the more accurate your math will be) required roughly 5-1/8 revolutions of the tire.

20/5.125 = 3.91