4.30 ratio to 3.73 ratio - Diesel Forum - TheDieselStop.com
'99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the '99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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post #1 of 30 (permalink) Old 10-28-2011, 02:52 PM Thread Starter
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4.30 ratio to 3.73 ratio

I have a F350 4x4 cc 2002. It has 4.30 ratio front and rear gears. I'm wondering if I was to find a wrecked F250 4x4 with 3.73 ratio front and rear gears. Will they fit into my front and rear diff. housing's or will I have to remove the ring gears off the f250 chunk and install them on my truck's chunks. This will be to improve fuel mileage. Any help will be appreciated. Thanks

John
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post #2 of 30 (permalink) Old 10-28-2011, 03:13 PM
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Is your truck a single rear wheel F350 with a gas engine?

2000 F250 Lariat CC SB 4x4 PSD Auto
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post #3 of 30 (permalink) Old 10-28-2011, 04:15 PM Thread Starter
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7.30 to 3.73 gear's

Sorry It is a dually and has the 7.3 diesel engine. I owned a 2001 F250 SRW 2WD with the 7.3 engine and it was getting 18.5 MPG and 16.5 pulling my 36ft camper. I needed a four wheel drive and while I was upgrading I whent with a F350 4X4 dually now this one is getting 15.2 mpg and 12 mpg pulling. I'm just thinking that my 2001 f250 with 3.73 gear would pull my camper with no problems. I did keep my chip and installed it in my f350. It helped a little bit on the fuel mileage. I found a wrecked f250 4x4 and was wondering if the gears would inter change with my f350. I know that the housings might be different due to dual rear wheels but not sure about the front.
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post #4 of 30 (permalink) Old 10-28-2011, 04:46 PM
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The gears from an F-250 won't fit an F-350 dually. Your F-350 should have either a 3.73 or a 4.10. Changing from a 4.10 to a 3.73 isn't going to make much difference in fuel mileage. It may not make any difference.

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post #5 of 30 (permalink) Old 10-28-2011, 04:52 PM Thread Starter
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My old truck 2001 f250 2wd has 3.73 gear and at 2000 rpm's I was rolling 67 mph and at 2100 rpm's I was rolling 72 mph. With my f350 4x4 with 3.30 gears i'm doing 62 mph at 2000 rpm's and 66 mph at 2100 rpm's.
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post #6 of 30 (permalink) Old 10-28-2011, 06:19 PM
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You will typically lose about 2 mpg going from 2 wheel drive to 4 wheel drive, and lose another 2 mpg going from single rear wheel to dual rear wheel. The mpg that you are getting with a cc drw 4X4 is as good or better than anyone else is getting. You have upgraded your off road capability, towing and payload, but unfortunately, you have to pay for it by losing some mpg.

2001 F350 XLT 4X4 crew cab, dual rear wheels, long bed, black, 7.3l turbo diesel, automatic transmission, 4.10, shift on the fly, running boards, sliding rear window, 38 gal fuel tank, Odyssey extreme 65-PC1750T batteries, Michelin LTX-MS2 rear tires, Sumitomo Encounter front tires, Shell Rotella Ultra elc, 11,500 gvwr, 20,000 gcwr, 7500 gvw, completely stock, 114,000 miles when purchased, now has 240,000 miles, repairs so far: two starters, batteries, cps, brakes, tires, alternator, ball joints, locking hub, wheel hub, AC compressor, serpentine belt, power steering pump, driver's side window, ignition switch, o-ring, Spectra premium radiator, water pump, fan clutch, fan blades, thermostat, thermostat housing, tensioner. Stolen twice so far, but recovered both times with major damage.

2005 Nomad Rampage toyhauler made by Skyline. 11,500lb gvwr.
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post #7 of 30 (permalink) Old 10-28-2011, 09:29 PM
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dont use used gears in a daily driver... unless the backlash is set the same as they were before they will make noise and wear out

2002 f250 ecsb 7.3,4r100 triple disc converter shift kit, amsoil atf, 60/10.5 DIY Tymar, (ISSPROboost, trans, Egt) PHP FU., Harpoon, hutch mods, ITP fuel pick up.
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post #8 of 30 (permalink) Old 10-29-2011, 07:02 PM Thread Starter
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I will buy after market 3.73 ring and pinion gears and rebuild kits for the front and rear. If I can drop my rpm's by 200 rpm's and still be running 65 mph, you can't make me believe that, that will not get me better fuel mileage. lower rpm's = higher fuel mileage. I know that this truck will pull my RV because I owned a 2001 f250 with 3.73 rear gears and it made better fuel mileage and handled the load great. I checked into kits for my truck and they will cost about $ 500.00 to $ 700.00 per axle. This is something I will install myself due to I've been working on 18 Wheelers for about 30 years. This will be done before I retire.
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post #9 of 30 (permalink) Old 10-30-2011, 02:55 PM
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lower rpm's = higher fuel mileage
You forgot the most important part of the equation, vehicle speed.

2000 F250 Lariat CC SB 4x4 PSD Auto
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post #10 of 30 (permalink) Old 10-30-2011, 04:21 PM
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Instead of the expensive gear change, just buy slightly taller tires. That is any easy "gear change"

Mongus rigs;
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post #11 of 30 (permalink) Old 10-30-2011, 04:53 PM
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is your mileage on this truck hand calculated or on the lie-o-meter? I have an 03 f350 7.3l dually crewcab with 4:10 gears and I only get 12-12.5. My old 99 f350 cc got 14-16 racing around with a chip. I was bummed with the fuel mileage I get, but I love the truck.

I have thought about changing gears or going to a taller tire, but I honestly do not think it will really help. JMO

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post #12 of 30 (permalink) Old 10-30-2011, 06:46 PM
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i am getting better milage with 35s than I was with 33s with 3.73s... turning about 2k at 70

2002 f250 ecsb 7.3,4r100 triple disc converter shift kit, amsoil atf, 60/10.5 DIY Tymar, (ISSPROboost, trans, Egt) PHP FU., Harpoon, hutch mods, ITP fuel pick up.
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post #13 of 30 (permalink) Old 10-31-2011, 10:02 AM
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Quote:
Originally Posted by Paw John View Post
I will buy after market 3.73 ring and pinion gears and rebuild kits for the front and rear. If I can drop my rpm's by 200 rpm's and still be running 65 mph, you can't make me believe that, that will not get me better fuel mileage. lower rpm's = higher fuel mileage. I know that this truck will pull my RV because I owned a 2001 f250 with 3.73 rear gears and it made better fuel mileage and handled the load great. I checked into kits for my truck and they will cost about $ 500.00 to $ 700.00 per axle. This is something I will install myself due to I've been working on 18 Wheelers for about 30 years. This will be done before I retire.
$1000-1400 will buy a lot of fuel for the minuscule improvement that gears will make.

'11 F250 CCSB Lariat 6.7 FX4
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post #14 of 30 (permalink) Old 11-03-2011, 06:54 PM
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Maybe my truck is strange but I usually average around 18MPG in mixed driving. Full highway I'll average around 20-21. I pretty much drive like a grandpa. I lost a MPG or so when I took my front bumper cover the truck came with off(Still have sunvisor and fairing), and General AT2s.

Evan-
2003 Ford F-350 Crew Cab L/B/Dually XLT FX4 7.3L/Auto- Gooseneck Hitch Fifth Wheel Rails, Firestone Air Bags/ Toolbox
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post #15 of 30 (permalink) Old 11-09-2011, 09:59 AM Thread Starter
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JUST FILLED MY TRUCK UP WITH DIESEL AND HAD PUT 468 MILES AND IT TOOK 29 GALLONS TO FILL IT UP = 16.14 MPG ON THIS TANK UP. I MADE A SMALL TRIP TO BATON ROUGE LAST WEEK OF 210 MILES ON INTERSTATE ROADS AND THE REST WAS LOCAL DRIVING. I KEPT IT AT 63 MPH AT 2000 RPM'S. I'M THINKING THIS IS REAL GOOD MILEAGE. GIVING SOME THOUGHT ON CHANGING THE RATIO TO 3.7. THIS WOULD TAKE ABOUT TWO AND ONE HALF YEARS TO PAY FOR THE UPGRADE IN SAVING. NOT SURE IF IT'S WORTH IT.
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