I would like to know what the gear ratio is in my 64 f100. I no longer have the tag on the rear end and I don't really want to take the rear end apart.

 

Do you still have the door tag? Axle code should be the # on the end of the first line.

 

The last # is a 1 I don't know if that is the orig door though

 

Here's a vin decoder with some info on it. Don't see just a 1 but look for yourself. If it doesn't work, cut & paste it. I haven't figured this link thing out yet.

http://www.home.earthlink.net/~jcpurut/vin/vin.html

 

10 is a 3.25, 11 is a 3.70, & A1 is a 3.73 could it be one of those? If it's only a one, someone else will have to help because I can't find it. Hope that link can help.

 

If your truck is not a locker, jack up your passenger side wheel. Make a mark on your driveshaft for a reference point where you can see it. Put your truck in neutral. Rotate your tire one full revolution. Count how many times your driveshaft turns. If it turns 3 1/4 turns, you have a 3.25. If it rotates 3 and 1/2, you have a 3.5. If it rotates about 3 and 3/4 turns, then you have a 3.70 (they didn't make a 3.75) You get the idea? If it is a locking rear end, then simply jack up both rear tires.

 

I'm sorry but I gave you the last # of the vin. All th eblack paint is gone on the door so I can only read the stamped out #'s. After looking at the decoder the # is A2

 

When I rotate the tire one rotation, the drive line only goes around a little over 1 1/4 times. I have a 292 with a three speed in the truck and it seems like I'm taking off in second gear

 

It should go at least 3 times. Does everything work once you get going and into other gears?

 

I am laying under the truck when I spin the tire. I have the tire and drive line both marked. One revolution on the tire and the drive line only goes around just over One and a quarter turn. It sounds like I'm going to have to pull the rearend and strart counting teeth. I can do 70 mph down the freeway at around 2000 rpm.

 

The only way that I have been successful at trying that method is start with the truck in a level place and roll the truck forward one wheel revelotion and count the shaft revs.

Caution, Please have another resposiable adult with you at the time in case something goes amiss while you are rolling and checking.

John

 

That's pretty weird. You have the right tire in the air? Try it the other way. Rotate the driveshaft as many turns as it takes, to turn the tire one full revolution. The least number of turns would be about 2 and 3/4, but that wouldn't be stock.

 

Whoa, fellas!!!

You are forgetting that when you hold one tire in an open diff, the other tire spins TWICE as fast.

It would seem that frig' has a very high rear, perhaps a 2.5 or 2.79.

Get a spool of fine thread or string. Tape it to the drive shaft, so that as the shaft turns, it winds string around the shaft. Jack up one wheel, and rotate that wheel 10 times. Now count the number of loops of string around the drive shaft. Divide that number by 5. You will have a pretty accurate #.

Sounds like its too high a rear. What engine you got? No one seems to like anything much higher than 3.00, and that is only for the fellas that like speed and never tow. The most common compromise rears are 3.50. Of course, a lot depends on your tires. If you put itty bitty small diameter tires on, you heed a higher rear, and conversely, if you put 33" tires on you need a much lower rear.

 

I have both wheels off the ground when I spin the wheel. I agree that I have to tall of gear. I'm tring to find out what I've got though. To do the string thing do I set one wheel back on the ground?

 

When you spin one wheel, are both turning, one forward, one back? You cannot have that happen when trying to determine rear ratio. If both are turning forward, try having a friend hold one. Can you still turn the other one (assuming the tranny is in neutral). If you cannot, or if it turns with great reluctance or "jerks" then you may have a locker (posi, in chevy terms).

You also wrote via email:
-------------------------------------------------------------------------------
It sounds like you know what your talking about. The truck has 295/50/15 all the around and is lowered. I've got to have it off the ground in order to see the drive line. I'm wanting to change the rearend because of the gearing. Will the 350 gears work best with that set of tires. I've got the 292 w3speed on the floor. Frigerator
__________________________________________________ ___________________

Those are indeed small tires, with a diameter of 26.6" At 70mph you said you were around 2000 RPM Using the following calculation:

gear ratio = RPM x tire diameter / MPH x 336

your ratio calculates to 2.26

My guess is that you are doing a little better than 2000 RPM, and you have a 2.5 or 2.79 rear. Whoever did that was a tad confused. You should be able to do about 100 MPH with that beast, if you want. You should verify the rear ratio, using the string method. I would guess that a 3.25 would be good for you, if you want to keep the samll tires. If you are looking at larger tires, then perhaps a 3.5

Good luck.