gear ratio
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Postmaster
Joined: Mar 2008
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From: LONG ISLAND N.Y.
gear ratio
helo all,i'm picking up a 2000 f350 crew cab lariet v10 this week.(can't wait)and i'm trying to figure out what gears are in my rears.i got some numbers off a tag thats on the rear cover.they are s138F 731059L26.
thanks in advance -ed-
thanks in advance -ed-
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Postmaster
Joined: Mar 2008
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From: LONG ISLAND N.Y.
thats what i'm doing.i have a 8000lb travel trailer.plus the truck has 35" x 12.5 x 16.5 tires so that kills the gear even more.i havent looked into it but i'm sure it would cost a lot to do both rears.what would you recomond?
Senior User
Joined: Feb 2008
Posts: 282
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From: Quad Cities, Iowa
Two ways to go.
1. Determine the speed you want to go when pulling a good load. The 2001 V10 made peak torque at roughly 2600 rpm. Your curve is probably pretty close to this. Then decide which gear you want to be in at that speed and torque. With that known, I can send you a spreadsheet that will tell you the exact ratio you will require.
2. Drop in 4:88 ring and pinion and you would be just about where 4:30 would have placed you at stock. Most years, the 4:30 was the tallest set Ford shipped stock on the 250/350. That will tow very nicely with the 35 inch tires.
I was running the 4:88. To get the same performance with forties, I had to move to 5;38 ratios. You will have to change both front and rear gears. Depending on what and who you use, expect to spend $600 to $1800 for the whole shebang.
For my needs, at peak torque in 5th gear I'm running at 65 mph. As a result, no matter how steep the grade or heavy the trailer, I'm guaranteed not less than 55 mph in 4th gear. On the rocks, I can still idle over many obstacles.
1. Determine the speed you want to go when pulling a good load. The 2001 V10 made peak torque at roughly 2600 rpm. Your curve is probably pretty close to this. Then decide which gear you want to be in at that speed and torque. With that known, I can send you a spreadsheet that will tell you the exact ratio you will require.
2. Drop in 4:88 ring and pinion and you would be just about where 4:30 would have placed you at stock. Most years, the 4:30 was the tallest set Ford shipped stock on the 250/350. That will tow very nicely with the 35 inch tires.
I was running the 4:88. To get the same performance with forties, I had to move to 5;38 ratios. You will have to change both front and rear gears. Depending on what and who you use, expect to spend $600 to $1800 for the whole shebang.
For my needs, at peak torque in 5th gear I'm running at 65 mph. As a result, no matter how steep the grade or heavy the trailer, I'm guaranteed not less than 55 mph in 4th gear. On the rocks, I can still idle over many obstacles.
Originally Posted by spinella
thats what i'm doing.i have a 8000lb travel trailer.plus the truck has 35" x 12.5 x 16.5 tires so that kills the gear even more.i havent looked into it but i'm sure it would cost a lot to do both rears.what would you recomond?
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Postmaster
Joined: Mar 2008
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From: LONG ISLAND N.Y.
overengineer,i tow at 60-65mph usually all flat.east coast(i have my wife and three kids in my truck too)plus i want to be safe.any info you can send would be appreciated.i'm not positive on what gear i have so when i pick the truck up wensday i'll jack it up and spin the tires and count.if changing gears is too expensive do you think i could put factory take off wheels and tires to give me a little more gear.(reduce tire height)?these forums are new to me.it's great all the good info you can get.thanks again.
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Senior User
Joined: Feb 2008
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From: Quad Cities, Iowa
Bringing the tires back to stock will help, however, if you have the 373 you will spend a great deal of time in 4th gear. Lord knows I did.
I grew up in New England. When did it get flat? Although, I'll admit the rockies will crush it...
I grew up in New England. When did it get flat? Although, I'll admit the rockies will crush it...
Thread Starter
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Postmaster
Joined: Mar 2008
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From: LONG ISLAND N.Y.
my truck is a 2000 so forth gear would be o.k.when i pick it up wensday i'll hook up to the trailer and give it a shot.when i said east coast i'm really long island no mountains.new england is a different story.we mainly stay close to the island and only do one big trip a year.$$$$$thanks for your help.
Senior User
Joined: Feb 2008
Posts: 282
Likes: 1
From: Quad Cities, Iowa
I just checked my hard drive. I must have moved those files to external storage. If you want them, let me know and I will do a more extensive search tomorrow.
The real win is that you are looking at final gear ratios. Most folks never do. I can't tell you how many times I've heard "I don't need gears, I have an automatic or... Why? it's a Massive Diesel!"
The 31" stock tires will make a real difference
The real win is that you are looking at final gear ratios. Most folks never do. I can't tell you how many times I've heard "I don't need gears, I have an automatic or... Why? it's a Massive Diesel!"
The 31" stock tires will make a real difference
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Postmaster
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From: LONG ISLAND N.Y.
overengineer,i tried e-mailing you but i don't have enough post yet.i got tht truck.theres a factory sticker on the axle tubes that says 3.73 ratio.if you still have time to show me that sprread sheet for tire/gear combos,i would love to see it.thanks.if somebody that can e-mail reads this can you please e-mail overengineer for me.thank you -ed-
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Joined: Oct 2001
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From: Washington State
Originally Posted by spinella
ken how did you figure that out?the door sticker has no number under the word axle.i was hoping for a steeper gear.thanks again.
The first two numbers of the second set of number you gave dictate the ratio. 73 meant 3.73. Some say that underneath that bolt you'll see the 3. but I've never removed mine to see. 
You can use this online calculator to help you determine tire & gear combo.
You'll need to know your tranny ratios. They can be found in the Super Duty FAQ on top of the Super Duty forum.