i know rearends have different sizes like 8" or 9" but i dont know what is actually being measured, i know people will prob. laugh at this, but i need to know.

 

it has to do with the size of the ring gear........ I think. I know that is the case with the 14 bolt rear axles (A.K.A. 10.5").

 

i believe your are right
it is the size of the ring gear
how come you need to know?

 

yes , it is the size of the ring gear, and the bigger the size, the tougher the componet. 8 1/4 to 8 3/4 then 9 3/4 dana.

 

They are tougher til you start getting into the higher gear ratios like 5.88 or 6.17 but who here will do that high in a street machine.

 

lol, the typical guy wouldnt, but then theres lways the exception to the rule. i knew a guy put a set of 5.36`s in a dana in a 68 gtx, 440, 4spd. wow.

 

That is just crazy. He may have been running some 33" tall slicks?

I am thinking about installing a set of 4.89 or 5.13 gears in a pair of D44s that I have for a crawler project but would never do that to a car.