Axle Ratios - Ford Powerstroke Diesel Forum
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Old 09-01-2013, 04:54 AM
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Axle Ratios

New guy here and got a question for the experienced haulers. I have an early 99 F-250 (Born on date 04/98) and am looking to change my axle ratios.

Little background on the rig. It has an 11" lift with BDS springs and Fox 2.5 shocks with reservoirs. Tires are 38" Toyo all terrains. Drivelines have been extended to meet the differentials at more normal angles. I bought the truck with an 8" lift and smaller shocks, but decided to crank it up higher since it's what I've always wanted. Yes the truck in the picture is a '99. The first owner had a '06 front clip and an '08 bed put on it. As well as plenty of goodies inside the engine compartment and inside the cab.

Anyways, I've looked at the sticker on the doorjamb telling me that it was factory installed with a C1 axle, which should mean it has stock 3.73 gearing. I was wanting to lower the ratio (higher numerically) to a 4.10.

It does have the 7.3 and I know this engine has way more power than I am feeling when pressing on the gas, obviously the larger tires are playing the major role in it. It just feels sluggish and I need to give it a good foot-full of pedal to make it accelerate at a reasonable rate. I've been reading up that swapping to 4.10 gears would provide more get-up-and-go as well as towing torque. If it ever decides to rain here in Nor Cal again I plan to play in some mud. I hardly tow anything as it is and don't use it for long highway runs. Maybe from Sacramento to Reno but that would probably be the farthest and only rarely. I'm told that if the ratio was lowered it would make this engine just scream when running at highway speeds. This motor is already pretty darn loud as it is now and I don't want to wring it's neck just for a highway cruise.

Any input if I should leave them or change them? How much would Ford or another shop charge to change the ratios in both axles?
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Old 09-01-2013, 06:02 AM
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If you are running 3.73 with 38's, I would definitely swap them out. 4.11 would be the highest I'd go, but you may be better served with 4.30. The difference will be ~90 RPM at 70mph, but you'll have a little better response at lower speeds. It will definitely serve you better going over the Sierra's. If you do much playing up there in the foothills, you'll like 4.30 better as well.

Randy's Ring & Pinion

*Edit*

Here's a calculator so you can crunch some numbers yourself. The "prime" cruising RPM is 1800-2200.

http://www.ringpinion.com/calculators/calc_rpm.aspx

Last edited by Macon; 09-01-2013 at 06:07 AM.
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Old 09-01-2013, 08:32 AM
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Bump to at least 4.30, otherwise don't waste your money for such a small change from 3.73 to 4.10. You won't notice much of a difference with such a small change and regearing isn't cheap.
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Old 09-02-2013, 12:49 AM
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Thanks for the input fellas. I looked at the site you linked Macon and there's only 2 brands for gearing USA Standard and Yukon. Any differences to know about the two? Also I saw the OEM gears are twice as much as the others, why is that?
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Old 09-02-2013, 01:00 AM
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OEM are supposedly better quality. Just what I've read.

You can also check out JustDifferentials.com and JeffsBroncoGraveyard.com

To do both axles, labor will probably be around 10hrs plus parts. Ford dealers obviously will have a higher rate.

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Old 09-02-2013, 01:17 AM
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Ok rookie followup question. Is this a Dana 50 axle? 60? 80? Sorry for all the questions but this is new to me and I usually like to learn about new stuff and look before I leap.
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Old 09-02-2013, 01:20 AM
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D50 unless someone has changed it out. I think they are called a "Super 50" iirc.

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Old 09-02-2013, 01:45 AM
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Ok good to know. The more I read the more I scratch my head now haha. Dana 50's on both front AND rear correct? Some other sites that pop up on a google search say the front was a 50 with no info on the rear. Should be the same for both right?
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Old 09-02-2013, 02:38 AM
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If you are going to "Play in the mud" and you are in the process of swapping gears you might as well throw in a Detroit E-Locker just for the hell of it. You could do both front and rear but if mud is all you are doing and not rock climbing then you could get away with a set of Truetrac's up front to save on some cost. Actually I think Eaton now recommends the M-Locker over Truetrac's. Either way you might as well look into it if you are already going to swap out gears. You won't be disappointed.

Differentials & Locking Differentials
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Old 09-02-2013, 02:52 AM
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Thanks for the info Lilfarmrboy. I still have a lot to learn.
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