rear gear identify

[fomocoguy]

So I may be going to look at a rear diff for my Fairmont project today, but the guy says he doesn't know what the gear ratio is. I was just thinking, to identify the gear ratio is it as easy as counting the spins of the yoke vs the spins of the tire, or is the ratio actually the number of teeth on the ring gear vs the number of teeth on the pinion gear? After writing this out and reading it to myself that sounds more likely, but I just wanted to see if any of you have an easier way than pulling the diff cover and counting the teeth. It's an 8.8 out of a 1987 5 speed Mustang vert. I don't think the tag has the actual ratio stamped on it. Thanks!

[FORDification]

If the tag is on it, use the following link to decode it.

http://www.fordification.com/rearends-ford01.htm

But yes, the ratio is determined by dividing the number of ring gear teeth by the pinion gear tooth count.

[fomocoguy]

Hey thanks Keith! I didn't realize you had that info here. That will help a lot in my search, since I think I'm going to go scout for rear ends at the junk yard monday and I can write the numbers down and check it out when I get home.

[FORDification]

Or you can just print those pages out and take 'em with you, that way if you find one that'll work for your project, you won't have to keep looking.

[ka_jd7and1]

I've started a binder of casting numbers and things to look for at the junkyard that I can take with me. I'm going to get the pages laminated (someday), so I can't get them all greasy.

[ezernut9mm]

if you can jack the car or truck up you can also count the number of driveshaft turns vs. the number of wheel turns. this isn't super accurate, but will give you a close estimate. i.e. if one rotation of the ds net you four rotations on the wheel than it is most probably a 4:11.