Rear End Ratio's.


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Rusty Driver
Rusty Driver

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Post Tue Nov 13, 2018 2:56 pm

Rear End Ratio's.

What is the way for figuring the ratio's on the rear ends? This is on a 46 K-2 with GD 214 engine. I think it has to do with tire revolutions and drive shaft revolutions but once you have that what is the rest of the formula? I recently got another rear end that may be out of a half ton PU and I was told it may have a higher ratio which would help in driving VS the 3/4 ton I have now.
Thanks for any information.

Golden Jubilee
Golden Jubilee

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Post Tue Nov 13, 2018 3:34 pm

Re: Rear End Ratio's.

If the rear or driveshaft is out, look on the head of the pinion for the tooth count. Then divide the smaller into the larger number for the ratio. Works every time and no guess work.

Golden Jubilee
Golden Jubilee

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Post Tue Nov 13, 2018 3:57 pm

Re: Rear End Ratio's.

Try this for reference. You should try and make Google you best friend. You most likely use Google to find this forum.
http://content.wisconsinhistory.org/cdm ... c/id/36871

The axle ratio your truck has may be one of the following three. 3:72/1, 4:18/1 and 5:11/1. The "!" represents one turn of the wheels. The other number is the number of turns the engine will make in high gear to turn the rear wheels one revolution.
If you have the original 600:16 tires, they should be 27.91 inches in diameter. This is about 88 inches circumference, or, 7.32 feet. 5280 feet in one mile divided by one revolution of the tire is 5280/7.32 feet is 721 revolutions of the tire in one mile. Now, multiply the axle ratio against 721 to get the number of revolutions for the engine in one mile. I hope this is correct. CB89 will be checking on me.
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Rusty Driver
Rusty Driver

Posts: 197

Joined: Thu Dec 07, 2017 3:58 pm

Post Wed Nov 14, 2018 2:18 pm

Re: Rear End Ratio's.

Thanks to both of you for this information.
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Golden Jubilee
Golden Jubilee

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Post Wed Nov 14, 2018 6:53 pm

Re: Rear End Ratio's.

Assuming your current rear axle is not posi-traction, here's how to determine the ratio:

Jack one wheel off the ground, put the transmission in neutral and take the parking break off. ***Be sure to use jack stands under the axle for safety precaution***
Mark the wheel and the drive shaft with chalk or masking tape.
Turn the wheel TWO revolutions and count the number of driveshaft turns.
The number of driveshaft rotations will help you determine your rear axle ratio. For example, if it turned 3 and a half times, it's a 3.50:1 ratio. If it turned 4 and a quarter times, it's a 4.25:1 ratio.
For better accuracy, turn the wheel 20 times and divide by 2 for your rear axle ratio.
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Golden Jubilee
Golden Jubilee

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Post Thu Nov 15, 2018 5:43 am

Re: Rear End Ratio's.

I like that Paul

Golden Jubilee
Golden Jubilee

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Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Thu Nov 15, 2018 8:16 am

Re: Rear End Ratio's.

The problem with spinning a wheel and looking at the driveshaft, is it can be hard to tell the differance between 3.7 and 3.54 or 3.9, . on a car it doesn't likely matter much other than engine rpm, but on a truck it can make a big difference. I gained nearly a MPG changing from 3.90's to 4.11's.
The tooth count never lies or is confused, it is what it is, and then you know. In about the time it takes to spin the wheel, you can look at the pinion head inside the nut holding the yoke on. Works on posi rears as well.

Rusty Driver
Rusty Driver

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Joined: Thu Dec 07, 2017 3:58 pm

Post Thu Nov 15, 2018 12:23 pm

Re: Rear End Ratio's.

Thanks for all the great information. I will pull the yokes off the 2 and see what I have.

Rusty Driver
Rusty Driver

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Post Mon Nov 19, 2018 3:35 pm

Re: Rear End Ratio's.

When I pulled the wheel ends apart the passenger side had no shims in between the backing plate and axle housing. The driver's side had several real thin paper type shims. I did not see them till I had it in the parts washer and those came off in pieces. I am calling them shims perhaps that is not right but why would one side have them and not the other? Also I am sure those cannot be purchased anymore but anyone have any ideas on what to use to perhaps make some?
Thanks for any help.
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Golden Jubilee
Golden Jubilee

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Post Mon Nov 19, 2018 10:29 pm

Re: Rear End Ratio's.

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