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Old 11-16-2007, 10:44 AM
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Okay, guys - I know this has to have been answered a million times, but I can't find it here anywhere right now. I'm trying to determine my 8" Ford ratio. With both wheels off the ground, I turn the axle and get 1.33 turns of the axle for each full turn of the u-joint! Now, I've heard of economy gears, but that's ridiculous.

I was told to take the rear end cover off and mark a tooth both on the rack and pinion gears with something (piece of tape or scratch with awl). and count the number of teeth for both of the gears.

re: Figuring rear axle ratio
It's a characteristic of non-posi rears. The wheel on the other side was probably turning the other way. They don't always turn the same amount as the one you have your hand on, either, so make sure it's immobile before you count. Then turn the tire TWO full turns while you count the drive shaft revolutions.

The above was copy-pasted from assorted postings from the first link I gave.

The following is not a 100% foolproof method, and will not get an "exact" numeric figure, but will get you very close. Basically, what you need to do is as follows. I plotted this out so I can make it easy for anyone to duplicate.

1. Park the car on a flat, level surface. Block the front and back of each of your front tires, and do the same to one of the rear tires.

2. Raise the unblocked side of the rear end (axle) of your car and firmly and securely supported on a jack stand. Never leave it supported on just the floor jack, that is very unsafe, and can result in serious injury or even death.

3. Put the car it neutral (engine off).

4. Mark the universal joint at one of the 4 bolts that hold the caps to the rear end. You can use a small piece of masking tape and place it over one of the 4 bolt heads.

5. Rotate the tire until you get the mark on the bolt cap to an easily identified and repeatable location on the rear end center section (the "pumpkin" in the middle of the axle). You can mark the pumpkin if you want to. The important thing to remember is to have a repeatable mark to stop on for easy reference.

6. Place a mark on the raised tire, running from the rim to the tread surface, running straight up at the 12:00 position. I use a helper (my "helper" is my wife) for the next step. It helps to have an extra set of eyes, but this can be done alone, just take your time and go slowly.

7. Spin the drive shaft two full rotations and count the number of times the marking on the tire spins.

If the tire spins roughly 2 and 3/4 revolutions, you will have a 2.73 axle ratio. Three and almost a half revolutions will give you a 3.42 rear ratio, and a spun tire of 3 and 3/4 revolutions will give you an approximate ratio of 3.73. By the same way, a 4.11 ratio would have the tire spin just over 4 times around to two times around by the marking on the bolt cap on the universal joint.

My '78 Monte Carlo had a factory ratio of 2.29 (about 2 and a third of a tire rotation).

Hopefully I didn't make this as clear as mud, and it helps you out.

In a while, Chet.
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