rear axle gear ratio... - Ford Powerstroke Diesel Forum
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Old 02-21-2008, 05:13 PM
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rear axle gear ratio...

How do I figure out what my truck has? I recently purchased a 2000 f250 supercab 4x4 and was curious what ratio it has.Thanks
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Old 02-21-2008, 05:21 PM
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theres a tag and sticker on the axles that have it on them most likely 3.73 ..if your around 1700-1800 rpm at 70 mph 3.73 if 2100-2200 4.10 assuming stock tire size and auto tranny anyway
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Old 02-21-2008, 05:25 PM
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If you look on the sticker in the driver side door jam, it will say AXLE on it, under it will say somthing like "C1". get that code and we can figure out what you have. there should also be a tag on the rear axle itself.
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Old 02-21-2008, 05:43 PM
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More than likely if it is a single rear wheel truck, it is 3.73. If it is a dually then it is at least 4.10. I trust the tag on the rear axle.
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Old 02-21-2008, 08:50 PM
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I've got a 2000 DRW CC and just got the build sheet yesterday on it and Ford tells me that I have 3.73's but I know that can't be because @70 mph I'm around 2,100. My 95 SRW CC is under 2K @ 70mph
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Old 02-22-2008, 05:47 AM
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My '99 srw xt cab has 3.73, with stock tires 70-75 is above 2100 rpm. I upsized to 295-70x16's to correct the 5% speedo error(read fast). I have seen older trucks with 3.55 rear ends, do the math to figure your rpm(rough on auto trans): Pi D of tire height for rotating diameter(circumference) divided into 5280x12(63360in.) for rolling rpm, divide your engine rpm at 60mph by this number for the rear end ratio. For auto trans the slippage will show as a increase from 3.73 or 4.10 by a small %.

This will also show any % variances in speedometers.
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Old 02-22-2008, 05:59 AM
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As reference:

38" tires- 3.14x38=119+or-, 63360/119=532+or-, 1900/532=3.57 rear end FINAL ratio.
3.55 would be 1888 engine rpm at 60 mph on a stick 1900+/-10-15 rpm on an automatic would be the same ratio but would show higher like 3.66 or 3.62 depending on slippage.

And like I said, speedometer variant % will show out with the formula.

To check speedo accuracy: known ratio (say 3.73) times known tire size revolution per mile (38's were 532) equals engine rpm at 60 mph: 3.73x532=1984.
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Old 02-22-2008, 01:55 PM
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Old 02-22-2008, 08:52 PM
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mine has a 3.73 open rearend.....

I made a thread over at PSN and here is the responses I got.... (the second post has what you need)
http://powerstrokenation.com/forums/showthread
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