8 3/4 rear end identification

[4Cruizn]

Do the numbers on the side of the pig indicate what gear ratio it is?   

[BIGSHCLUNK]

That would make things easy now wouldn't it?    

[mrbill426]

No, they put a metal ratio tag under one of the upper carrier-to-housing retaining nuts.  If it is missing you can still rotate the input pinion and count the revolutions it takes for the wheel to make to make one complete turn, then do the math.

 

Do the numbers on the side of the pig indicate what gear ratio it is?   

[HP_Cuda]

Short answer = yes

Otherwise someone may have swapped out the pig/chunk and kept the tag there and hence will be wrong.

[4Cruizn]

Short answer = yes

Otherwise someone may have swapped out the pig/chunk and kept the tag there and hence will be wrong.

So pretty much need to pull the pig out and do the math to be sure . . . . What is the formula to determine what it is?   

[HP_Cuda]

You need to put the rear up in the air and rotate one of the tires and see what the other tire is rotating to said ratio.

Good read and also goes over open rears vs limited slip:
http://www.how-to-build-hotrods.com/gear-ratio.html

[mrbill426]

I am pretty sure that you simply divide the wheel rotation by the pinion rations, if you have 4 pinion rotations to achieve 1 wheel rotation, you have  a 4 to 1 gear ratio.  The closest Mopar gear-set would be a 4.10.
Am I off base guys??? 

 

So pretty much need to pull the pig out and do the math to be sure . . . . What is the formula to determine what it is?

[jhaag]

MrBill is correct. Very simple equation.

[4Cruizn]

Ok that sounds pretty easy but what if the pig is for sale at a swap and not in the rear?

[falkenracing]

The ratio is stamped on the ring gear if I'm not mistaking, so if it's out, you will be able to see it.

[BIGSHCLUNK]

Ok that sounds pretty easy but what if the pig is for sale at a swap and not in the rear?

Divide the ring tooth count by the pinion tooth count....     Originally I thought you wanted to know by looking at the embossed numbers on the casting. Ya, I know tags can be long gone!

[4Cruizn]

Divide the ring tooth count by the pinion tooth count....     Originally I thought you wanted to know by looking at the embossed numbers on the casting. Ya, I know tags can be long gone!

That was my initial question, I am currently tearing one apart . . . My first . . . And just assumed that the numbers on the outside of the center section would tell you the gear ratio.  I have already pulled the axles but assume I can just stick one back in and make a revolution to determine ratio.  I think I was told it is a 3.55 ratio. 

[jhaag]

Put a mark on the ring gear. put a mark on the pinion yolk. rotate the ring gear 1 revolution and count how many times the pinion yolk goes around. 3.5 rotations of the pinion yolk and it is a 3.55 to 1. Easy peasy. Ratio will also be stamped into the ring gear. casting numbers on the carrier have nothing to do with gear ratio.

[BIGSHCLUNK]

I;ve had times that the spin and count method can be a little tricky. EXAMPLE... 3.23 -3.55 like a hair of a turn.....

[anlauto]

I've always found it easier to leave the rear wheels on the car. Do one full rotation of the wheel and count the rotations of the yoke. 3:23's would be 3 1/4 while 3:55's would be 3 1/2, pretty easy to tell the difference.