I have a 81 f100 and the axle code on the door says "02". Does anyone know what the ratio for this axle is. I would really like to know.
Thanks

 

I just got back from another forum and I think this might be a 3.55 ratio.
What axles did the 5 lug nuts apear on in 1981?
Maybe that could help me, because I have either 5 or 6 studs I am not sure. I have never taken one of the wheels off on this truck, but I remember that there are very fiew lugnuts.

 

I don't recognize that code from 1981. Does your axle have a metal ID tag on it, that you can get the numbers from? IF it has a cover plate bolted onto the back (Ford 8.8") the tag will be on one of the bolts. I'm thinking you should have a Ford 9" axle, so the tag is bolted on the front side next to the driveshaft, There are no bolts in back, as the cover is welded on as part of the housing. I have that axle in my gallery if you need to see a pic.

 

yea, it looks like a 9in, and for a while there I thought it was a 2.73 ratio. But when I drive at 55 mph it sounds like the engine is dooing abut 2500 or 3000 rpm's. I do not have a tach in the truck, so I do not know if what I am hearing is right, and their is a huge hole in the exhoust right before the muffler, so what ever I am hearing might be an exageration of what is really going on. I am looking at putting in a new trans so I need to know what the ratio is. I looked for a tag when I first got the truck but had not luck, I will try again and hopfully I just overlooked it the first time.

 

just jack the thing up and spin the wheels and measure how many times the driveshaft spins. It is easier than trying to read some half destroyed tag.

 

Code "02" in 1981 is an open differential 9 inch axle with 3.00:1 gears rated at 2800#.

 

Well, there is no tag on axle. I did not do the spinning test but I will try it. As for it being a 3.00 you might be right, the rating on the door tag for the rear axle is 2534 lbs, is there anyother axle that had this rating. I am just trying to get all the info I have together so I can determine the ratio of this.
With the spinning test, do I have to have both wheels of the ground in order for it to be accurate, or do I only have to have one wheel up. I know that the one that is easiest to spin will spin in the open axle styles, but will it cause the wheel to spin any faster or slower if only one is spinning as oposed to them both?
thanks for the help

 

Where did you find that info? I'd like to keep that for reference.

ANd I think looking for a tag is a heck of alot easier than placing a jack under the axle and spinning the wheels. Reading it may be another story, though. You need to get both wheels off of the ground. They should turn opposite directions if you have an "open" diff.

 

If you have an open diff, and have both wheels off the ground, the wheels will spin opposite of each other, and the drive shaft will not turn. You need to block one wheel from turning. I tried this on my truck, and I came up with a 1:1 ratio, so I know I didn't do something right. Usually, you turn the wheel 1 revolution, and count how many times the drive shaft rotates, that will give you the ratio. But like I said, my experience with it is flawed. I suppose I need to get under there with some degreaser and find the tag.

 

I just tried that test, and I got about I 1:1 ratio. I know that the driveshaft did not even finish turning when the wheel had done 1 complete revolution.
I even tried having both wheels off the ground, and spining the axle, but I could not get both wheels to spin evenly like it would do when going down a strate road.
Has anyone else got any suggestions?

 

Boss is correct.Here's the code link.

https://www.ford-trucks.com/forums/s...d.php?t=297637

 

Thanks.
No offense to anyone, it is just that I always like a second opinion before I settle with one answer being the absolute truth. If I can get 1 person to back up someones idea, then I am happy, if I can get 2 peaple to back it up, then I am even happier. You know what I mean.
Purple55 thanks for that link. I checked the sight specs section, and there was almost nothing in there. The info you posted can really help me in the future.

 

You have to spin the driveshaft once, count the number of wheel revolutions, and divide by two. That's your ratio.

The reason you have to divide by two is because when you're traveling down the road, both wheels are spinning, but when one wheel is blocked, the other wheel has to spin twice as fast. It's just the way open diffs work.

 

One thing I don't understand about the way you are describing. I have already tried that method. I had one wheel up off the ground, I made a mark on the driveshaft and the pumpkin, and I made a mark on the tire, and the ground. Then I started to spin the driveshaft, and my partner who was watching the tire said that the tire was realigned with it's mark, but I had only made one spin with the driveshaft.
That would make it 1:1, so if I divide by 2 then it would be a .5 ratio. But according to my calculations, I should be getting about 1967 rpm's at 65 mph with a .81 4th gear, 215/75/15 tires, and a 3.08 rearend. But I think I am doing around 2,000 rpm's at around 60mph. Now it is hard for me to judge how fast the engine is going because I do not have a tach, and I have a really bad exhoust leak, and I am used to a 4cylinder, or 6. I have not really had the chance to set the rpm's on a v8 and then being able to look at the dash and see if my guess is correct.

So am I doing something wrong with the this, or should I just hope that either my partner or I did not see something right when we tried it the past 3 times. I will try again tommarow and just hope we missed something. But untill then, just to make sure I got this right, I spin the driveshaft 1 complete turn, count how many times the tire went around and then divide by 2, or do I spin the tire 1 complete revolution and count how many times the driveshaft spins.

 

Something I started thinking about. If you spin the driveshaft 1 turn, and the wheel turns 2 revolutions (I picked these numbers for easy math) then you divide by 2, that would make it a 1:1 ratio wich would be good for high speeds. But in order to get a 3.00 ratio, the tire would have to spin 6 revolutions for every 1 that the driveshaft does. But a 1.00 ratio is supposed to be better for high speeds than the 3.00, and yet the 3.00 would make the tires spin more acording to the method you described earlier.
So woud't it be that you spin the tire, and count how many time that the driveshaft spins.
But then my question is, would the amount of revolutions the driveshaft make be the ratio, or would you divide or multiply by 2 in order to compansate for only the one wheel spinning?