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03-02-2013, 01:35 AM
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#1 |
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Registered User
Join Date: Feb 2013
Location: Crawford Texas
Posts: 4
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Rear gear ratio
How can I figure out what rear end ratio my recently purchased 84 C20 has? It's a 4spd in the floor. The sticker in the glovebox is gone this is my first time on a forum so if I got in on a wrong thread sorry, been driving chevrolet 3/4's my whole life got an 05 I bought new also. Great truck. Have been wanting this 84 I have now for some time, it has 52,000 actual miles Very proud!
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03-02-2013, 01:41 AM
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#2 |
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Registered User
Join Date: Jul 2010
Location: Lafayette, IN
Posts: 622
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Re: Rear gear ratio
Congratulations! The best way I know to figure out the ratio is to jack the right rear off the ground. Mark the driveshaft and the tire. Then turn the tire while counting the number of revolutions the driveshaft makes. That should get you a pretty good idea of what ratio you have.
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03-02-2013, 01:55 AM
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#3 |
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Registered User
Join Date: Feb 2013
Location: Crawford Texas
Posts: 4
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Re: Rear gear ratio
Thanks, I've always heard of doing that. I think you've sent me over the edge, I'm gonna do it tomorrow. My 17 yo son and I'll get a kick outta doing that. I was hoping maybe from a vin code or stamping somewhere too. Thanks again
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03-02-2013, 03:11 AM
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#4 |
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Registered User
Join Date: Sep 2010
Location: Lake Tahoe, Nevada
Posts: 755
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Re: Rear gear ratio
Just realize that if you have a limited-slip rear end, it will be very difficult to turn one wheel while the other is on the ground. An open differential will turn really easy.
Also, because of the way the differential works, if you're only turning one wheel you need to turn it TWO FULL revolutions, and count the driveshaft revolutions. So if you turn the wheel two full revs, and the driveshaft turns 3 and about 3/4 turns, then you have a 3.73. When it comes to calculations like this that aren't real precise (that last revolution was somewhere over a half, but not quite three quarters...) more is better. What I do is usually turn the tire 6 times and divide by 3, or even 8 times and divide by 4. So if you turn the tire 8 times, and you get 12 1/3 revs for the driveshaft, then divide 12.33 by 4, you'll get 3.0825, and look up common gear ratios, you'll see you have a 3.08
__________________
I know a little about cars, but if you have a question about electricity or sport quads, I'm your man!!! |
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03-02-2013, 10:26 AM
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#5 | |
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Moderator
 
Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,977
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Re: Rear gear ratio
Quote:
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And please let us know if and how your repairs were successful. |
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03-02-2013, 11:46 AM
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#6 |
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Registered User
Join Date: Jul 2005
Location: CT
Posts: 278
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Re: Rear gear ratio
Why not pop the cover and service it at the same time? The #s will be stamped on the ring gear. Drive over drive 41 : 11 = 3.73:1
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