ID of a axle

[63chevystepside]

Iv got a 75 gmc 3/4 ton and im looking to see what rear ratio it has-its a 14 bolt Hot Rod said it was 410 or something like that-and im just twindling my thrumbs and had some spare time. I cant find any numbers on the axle tub-found some on the diff-3977323 had CFD above it and just the numbers 66 by them self in that area. Guessing thats not the numbers im looking for but must be on the tub hiding. This rearend suppose to have like 3.42 on up to like a 5.13 i think-but id just like to know what exactly it is. I looked to the glove box and there is rpo codes there but none for rearend-any suggestions out there?

 

[66nova]

Are the gears out or does it have the drive shaft in it?

 

[PenguinLTZ]

Are there any numbers stamped on the end of the pinion? Right at the end, by the nut.

 

[Stumpuller6.5]

if its easy enough pull the cover and count the teeth on ring and pinion, divide the numbers and find the ratio!

 

[PenguinLTZ]

Many had the 2 numbers stamped right on the end of the pinion, you just divide the 2 numbers

 

[64shortbed]

hold one axl still (one tire on the ground) jack up the other side. put a mark at the top of the tire or axl. put a mark on the yoke. turn the axl one ful round and watch the yoke. if it takes the yoke 3 1/2 times to go around to 1 turn of the tire then its got 3.50:1 gears if it tat 4 1/4 turns to one turn of the tire then its close to being 4.11:1 gears etc....

 

[Stumpuller6.5]

most common were 3.73 and 4.10. i had 3.23`s in one that used to have a 6.2 diesel. not sure what options you would have to get lower than 4.10s!

 

[63chevystepside]

I thought bout doing the tire spin thing but no engine,its a stick, and its uphill could do it maybe one tire up like you said didnt think bout that-da-don't you hate it when its staring you right in the face. Don't have cover off either i could do that. Isnt there suppose to be some numbers on the short tub(d/s)?-I think i do that jacking up thing real quick-be right back with the info.

 

[64shortbed]

i was given an example of how to get a ruff idea of what may have. i dont know what they will have but its a way of finding out. thats how i know the rear end i bought for my 83 monte carlo ss had 3.23 in it before i took the cover off to make sure everything was ok.

i miss that car!!

 

[64shortbed]

I thought bout doing the tire spin thing but no engine,its a stick, and its uphill could do it maybe one tire up like you said didnt think bout that-da-don't you hate it when its staring you right in the face. Don't have cover off either i could do that. Isnt there suppose to be some numbers on the short tub(d/s)?-I think i do that jacking up thing real quick-be right back with the info.

you dont need the engine!! lol i guess i forgot to say to have the drive shaft disconnected lol!