rear end gear ratio

[Fordguy85]

So i am having trouble figuring out what the gearing on my rear end is, the dif cover says its a dana 60 rear end and has the code for a 3.73 , However the code on the tag says its a rear end for a 4x4 F250 mine is not a 4x4 , so I got to looking around on it a little more and there are other numbers stamped on it , and one that kind of makes sense has 2.15 72 now this truck was sold to me as a 72 , but its a hodge podge of truck parts thrown together, I marked the top of the tire and a spot on the drive shaft, the drive shaft goes around 2 times for one full tire revolution , so is my rear end a 2.15 ??


if thats the case , is that a good rear end ratio to have for , towing, gas milage etc ?

[BobbyFord]

Pull the cover off and count the teeth on the pinion and ring gears.

[tnlprt]

What Bobby said
Remove all doubt

[Fordguy85]

was really trying to avoid doing that

[tac]

I think the drive shaft will turn half because of the spyder gears, but I'll have to think about that a little. In that case I think it's closer to 3.73.

[tnlprt]

20 minutes later after a new gasket and fresh
gear lube your questions will be answered

[BobbyFord]

was really trying to avoid doing that

Either you want to know or not.

[Fordguy85]

was really trying to avoid doing that

Either you want to know or not.

I know there are other ways to figure it out other than pulling the cover off and counting the teeth, but if thats what i have to do thats what ill do, what type of gear oil goes back into, whats in it now is way thicker than what i have in my 05 f150 i have 75w 140 and 80w 90 for the front and rear for my 05 but i know back in the 70's they were different

[sargentrs]

Plain on 90w gear oil. Ahhh...simpler times.

[tac]

If its a standard differential, jack one wheel up and turn the wheel twice. If its a posi jack up both wheels and turn the wheel once. Watch the drive shaft if it turns not quite 4 turns (3.73) or if it turns a little more than 2 (2.15). If you want a more accurate number just turn the wheel more times.

[Fordguy85]

Plain on 90w gear oil. Ahhh...simpler times.

wasn't there some sort of modifier in it too , I can't remember what exactly its called but my dad was telling me that if it was a certain type of rear end it needed some sort of modifier additive in it too, can't remember what the heck he called it or said about it

[sargentrs]

The TracLoc differential (limited slip) has clutch discs in that needed a friction modifier additive. Standard (single wheel drive) did not.

[Nitekruizer]

Yeah, if you have a limited-slip differential, or what is commonly referred to as "Posi", you will have to use a Limited-Slip Differential additive. Read the labels. I've seen some bottles of gear oil that have the additive in them already. Anyway, it should be available where they sell 80W-90 gear oil, ATF, etc.

There is a mathematical formula for figuring out the rear gear ratio, but you will need to know your tire diameter in inches and your exact engine RPM at 60 MPH. It works best with manual transmissions, but with an automatic it will still be close. I can't remember the formula, but you can find it on the internet. Good luck

[Fordguy85]

The TracLoc differential (limited slip) has clutch discs in that needed a friction modifier additive. Standard (single wheel drive) did not.

If i don't have posi and i use a gear oil that has a friction modifier in it will it cause damage ?

[BobbyFord]

No, but why would you?