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Old 08-04-2021, 09:04 PM   #31
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Cant find the post but THANKS to whomever posted the link to the FordVinDecoder for me!
(Think I looked at every other decoder but the Ford one).
Only further confusion is the quigley conv putting the F250 axles on... ? I’m good with it tho
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Old 10-10-2021, 12:33 AM   #32
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Re-gearing from 3.73 to 4.10

So I find myself needing new tireís a little sooner than I had anticipated and came across this thread that almost answers my question. Iím currently running
265/70r17 on a quigley, 5.4, 3.73 rear end with an agile rip kit. Iíd like to bump them up to 285ís and try it for awhile. If I understand this right, using the formula laid out by itchy feet the new tires would give me the equivalent of a 3.99. It seems pretty insignificant but Iíd hate to trash the tranny in a test. I actually need to move the van from Boise to Phoenix before I could get into a shop, any thoughts?
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Old 10-10-2021, 01:58 AM   #33
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Edit: Just re reading your post - If you meant you would have to move to 3.99 (4.10 being the closest) to maintain similar rpms at a given speed you are correct. Perhaps I mis-read into what you were saying.

The larger 285 tires will drop you closer to an effective ratio of 3.55 in your 265 vs 285 w 3.73 calc. Your engine rpm will be less at any given speed and your acceleration will be slower due to the larger circumference.

Starting at stock config: By stepping your tires up to 265 from the stock 245 tires w the 3.73, your new effective ratio /rpms would be roughly equivalent to 245 w 3.55 gears. Now going to 285's you are around rpms of 245 and 3.33 (rough guess). There are gear ratio/tire calculators online to get the exact numbers.

Unless you are towing, running very heavy, or already have tranny issues there should be no concern w your tranny.
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Old 10-10-2021, 09:25 AM   #34
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I've been running 5.4L 3.73 gears 4R75 transmission with 285/70/17's for about 7 years without any transmission issues.
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Old 10-10-2021, 09:54 AM   #35
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Thanks 1der and boy wonder, I appreciate the feed back. That’s all good. I’ll drive it awhile and see how the performance and mileage change.
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Old 10-10-2021, 04:54 PM   #36
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I'm running 285's on my 2001 5.4 originally equipped with 373's. With the 373's, the speedo was off, but when I changed to 410's, the speedo was within one mph of being correct at 60mph making me think I'm back to where it was with stock tires and gears. There's less downshifting in the mountains now and better acceleration. In my case I'm quite happy with the lower gears, and I don't tow. If I did, I might go even a bit lower.
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Old 10-28-2021, 11:56 PM   #37
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I made the switch on tires to 285ís then drove it from Boise to Salida and hereís what I found. With the original gearing at 373 the performance is definitely not what it could be. Not that Iím a heavy foot off the line but sometimes, like merging or trying to get ahead of that truck, you need a little pep and going from 265 to 285 definitely made a difference. Hills are also a tougher nut to crack. Mileage didnít seem to change all that much. Iím leaning towards changing out to 410 and if I can find a rear end possibly switching to full float. Does anyone have a recommendation for a Phoenix area shop that can do the work?
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Old 10-29-2021, 09:38 AM   #38
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Quote:
Originally Posted by Eatmorefish View Post
I made the switch on tires to 285’s then drove it from Boise to Salida and here’s what I found. With the original gearing at 373 the performance is definitely not what it could be. Not that I’m a heavy foot off the line but sometimes, like merging or trying to get ahead of that truck, you need a little pep and going from 265 to 285 definitely made a difference. Hills are also a tougher nut to crack. Mileage didn’t seem to change all that much. I’m leaning towards changing out to 410 and if I can find a rear end possibly switching to full float. Does anyone have a recommendation for a Phoenix area shop that can do the work?

I just finished my 3.73 to 4.10 conversion. 5.4L 285/70-17's. I'm very pleased, much improved. The van still downshifts on steep climbs out of OD but no longer shifts down to 2nd and I can maintain speed up the grades much better. The speedo error is less than 5% compared to 10% with 3.73s (the actual speed is still slightly higher than indicated by speedo). Haven't checked mileage yet but won't be going back to 3.73s anyway.


If you are inclined to do this yourself the ring & pinion sets are between about $180-$300 depending on brand. $300 is for OEM Spicer. ..and if you are in there may as well do bearings and seals.


3.73's are 11 tooth pinion and 41 tooth ring 41/11=3.73 4.10's are 10 tooth pinion and 41 tooth ring 41/10=4.10. The ring and pinions are matched sets.



I bought everything from either East Coast Gear Supply or Denny's driveshafts....both online.

I bought shim kits, bearing puller, setup bearings/races, grease paint and a few other bits and bobs to do this; I'm planning on listed that stuff on CL and Ebay so if anyone here is interested please PM me.

There is tons of info online to do this job, it's not rocket science or voodoo, but it's tedious. There are three places that you shim, and each time you shim one it changes the others. So lots of installing/removing.
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Old 10-29-2021, 09:56 AM   #39
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Thanks boywonder, I’m happy to hear the conversion ended with the desired results. If I had the van home I’d probably do it myself but don’t have the tools or the place to do it, hoping to find a good shop in the phoenix area.
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Old 10-29-2021, 11:46 AM   #40
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When I went with 35's on my 5.4l I decided to move to 4.56.
Based on a lot of readings and checking conversion tables for gearing vs. rpm, 4.10 would bring you "back to normal" for 33's and for 35's it would have been a bit off. Seeing that I also wanted to have some more torque when loaded and uphill in the wild, I accepted the slightly high rpm and that the speedo is off.

All in all:
- Speedo always showing 5% higher speed that comparing to my phone GPS speed app
- RPMs vs. true GPS speed:
77 mph --> 2.500
72 mph --> 2.400
68 mph --> 2.300
59 mph --> 2.000

I know 35's are not so common, but I saw others with 33's and the whole ride offroad seemed to be a bit more rugged and mine seemed smoother.

Perhaps that helps anyone.
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