what gears do i need
Post Fiend
Joined: May 2009
Posts: 5,470
Likes: 3
From: Pea Ridge, AR
I would think you would want something pretty high like 4.88s, but here's one way to find out what you have
Superduty Codes
F350 duallys
61 - open - 3.73
62 - open - 4.10
63 - open - 4.30
F1 - Limited slip - 3.73
F2 - Limited slip - 4.10
F3 - Limited slip - 4.30
F350 SRW
41 - open - 3.73
42 - open - 4.10
43 - open - 4.30
D1 - L/S - 3.73
D2 - L/S - 4.10
D3 - L/S - 4.30
F250 & Excursion
31 - open - 3.73
32 - open - 4.10
33 - open -4.30
C1 - L/S - 3.73
C2 - L/S - 4.10
C3 - L/S - 4.30
You can also get the information from the tag on the differential.
Here's an example
S409B
3L73 102 8C11
The break down of these codes:
S409B:
S = Sterling Differential
409 = Print Number (Model Number)
B = Revision Identifier (Change in Design)
3L73:
3L73 = 3.73 Ratio
L = Limited Slip
Absence of L = Open Differential.
102: Denotes the ring gear size. 10.25 inches. 105 would be a 10.5 inch ring gear.
8C11: is the build date.
8 = year of manufacture. In this case it means 1998.
C = month of manufacture. A= January, L= December so C= March
11 = day of manufacture. So My differential was manufactured on March 11, 1998
Superduty Codes
F350 duallys
61 - open - 3.73
62 - open - 4.10
63 - open - 4.30
F1 - Limited slip - 3.73
F2 - Limited slip - 4.10
F3 - Limited slip - 4.30
F350 SRW
41 - open - 3.73
42 - open - 4.10
43 - open - 4.30
D1 - L/S - 3.73
D2 - L/S - 4.10
D3 - L/S - 4.30
F250 & Excursion
31 - open - 3.73
32 - open - 4.10
33 - open -4.30
C1 - L/S - 3.73
C2 - L/S - 4.10
C3 - L/S - 4.30
You can also get the information from the tag on the differential.
Here's an example
S409B
3L73 102 8C11
The break down of these codes:
S409B:
S = Sterling Differential
409 = Print Number (Model Number)
B = Revision Identifier (Change in Design)
3L73:
3L73 = 3.73 Ratio
L = Limited Slip
Absence of L = Open Differential.
102: Denotes the ring gear size. 10.25 inches. 105 would be a 10.5 inch ring gear.
8C11: is the build date.
8 = year of manufacture. In this case it means 1998.
C = month of manufacture. A= January, L= December so C= March
11 = day of manufacture. So My differential was manufactured on March 11, 1998
Posting Guru
Joined: Jan 2007
Posts: 2,364
Likes: 3
From: Gilbert Az.
With the 40"tires I think you would want to be running at least 5.88 if not 6.30's you didn't mention if you had an auto or manual trans. I would be on the safe side and do the 6.30's at least with an automatic. Hope this helps!
Jim
Jim
Thread Starter
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Freshman User
Joined: Jul 2011
Posts: 26
Likes: 0
I know this first hand, I just had mine rebuilt. Not a fun week at all. Does anyone suggust a good gear or website to buy one.
Are they fairly simple to install
Post Fiend
Joined: May 2009
Posts: 5,470
Likes: 3
From: Pea Ridge, AR
Randy's Ring & Pinion. The Differential Experts. Auto Parts & Services. They should be able to help you out.
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Posting Guru
Joined: Jan 2007
Posts: 2,364
Likes: 3
From: Gilbert Az.
Looks like 5.38's may be the lowest you can go, and that will probably be fine, since I have a tendancey to be way over cautious anyway! But a call to Ranry in the AM can answer all your questions. Their good people I've been buying from them for years no problems ever
Jim
Jim
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Hotshot
Joined: Mar 2007
Posts: 10,101
Likes: 40
From: Pa
You waved bye bye to fuel mileage when 40s were put on the truck.
A set of 5.38s with 40" tires will be similar to having 4.30 gears with 32" tires. A set of 5.13s with 40" tires is similar to 4.10s with 32" tires. So either the 5.13 or 5.38 gears would work ok for you. Myself I would probably lean towards the steeper 5.38s since you plan on towing and if you might go larger in the tire size in the future. Some guys on Pirate 4X4 may already have a similar setup to yours.
Unless they were taken off your front and rear diff covers should have a tag on them with the axle ratio. The tag is held on by one or two of the diff cover bolts.
A set of 5.38s with 40" tires will be similar to having 4.30 gears with 32" tires. A set of 5.13s with 40" tires is similar to 4.10s with 32" tires. So either the 5.13 or 5.38 gears would work ok for you. Myself I would probably lean towards the steeper 5.38s since you plan on towing and if you might go larger in the tire size in the future. Some guys on Pirate 4X4 may already have a similar setup to yours.
Unless they were taken off your front and rear diff covers should have a tag on them with the axle ratio. The tag is held on by one or two of the diff cover bolts.
FTE Leadership Emeritus
Joined: Sep 2003
Posts: 12,246
Likes: 761
From: Houston, Texas
Using the formula (new tire size/old tire size)x current gear ratio= new ratio
If you're looking for the equivalent of 3.73s:
(40/31.5)x3.73= 4.73, the closest match being 4.88. This match will put you a little higher in the RPM range which will help around town and while towing. Anything higher than this is probably overkill and may do more harm than good.
If you're looking for the equivalent of 4.30s:
(40/31.5)x4.30= 5.46, the closest match being 5.38. This match puts you a little under the target for 4.30 gears, but will definitely get you the desired effect if you tow alot.
A little off topic, but I've learned alot about gears and proper calculations the hard way:
Start at post #62 and work your way down and over to the next page. I was dead on right at post #77 and started second guessing myself at post #81. I shot myself in the foot and made an expensive mistake at #88 and wouldn't realize it until post #102. Post #104 offers more details on why it didn't pay to go higher.
https://www.ford-trucks.com/forums/6...y-caved-5.html
If you're looking for the equivalent of 3.73s:
(40/31.5)x3.73= 4.73, the closest match being 4.88. This match will put you a little higher in the RPM range which will help around town and while towing. Anything higher than this is probably overkill and may do more harm than good.
If you're looking for the equivalent of 4.30s:
(40/31.5)x4.30= 5.46, the closest match being 5.38. This match puts you a little under the target for 4.30 gears, but will definitely get you the desired effect if you tow alot.
A little off topic, but I've learned alot about gears and proper calculations the hard way:
Start at post #62 and work your way down and over to the next page. I was dead on right at post #77 and started second guessing myself at post #81. I shot myself in the foot and made an expensive mistake at #88 and wouldn't realize it until post #102. Post #104 offers more details on why it didn't pay to go higher.
https://www.ford-trucks.com/forums/6...y-caved-5.html
Thread Starter
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Freshman User
Joined: Jul 2011
Posts: 26
Likes: 0
i dont tow the trailer all the time, probably 2-3 times a week. but i live in Colorado so hills are everywhere, sometimes steep inclines. im gonna be taking a road trip soon and will be pulling the trailer to Texas, I just dont want to blow the tranny again. Im looking for a good gear match that's good for everyday driving and towing.
I dont know jack about gears or ratios, the truck pulls itself well without the trailer, but can easily jump rpm's when trying to climb or speed up, its heavy and 40"mtr's arnt light
I dont know jack about gears or ratios, the truck pulls itself well without the trailer, but can easily jump rpm's when trying to climb or speed up, its heavy and 40"mtr's arnt light
FTE Leadership Emeritus
Joined: Sep 2003
Posts: 12,246
Likes: 761
From: Houston, Texas
i dont tow the trailer all the time, probably 2-3 times a week. but i live in Colorado so hills are everywhere, sometimes steep inclines. im gonna be taking a road trip soon and will be pulling the trailer to Texas, I just dont want to blow the tranny again. Im looking for a good gear match that's good for everyday driving and towing.
I dont know jack about gears or ratios, the truck pulls itself well without the trailer, but can easily jump rpm's when trying to climb or speed up, its heavy and 40"mtr's arnt light
I dont know jack about gears or ratios, the truck pulls itself well without the trailer, but can easily jump rpm's when trying to climb or speed up, its heavy and 40"mtr's arnt light
When I was lifting my truck, I did a little planning beforehand and added a few things to help my trans handle the additional load.
I added a sonnax/tricumulator shift kit and 26row 6.0 trans cooler. This helped firm up the shift and keep it cooler at the same time. My original trans went out at 127K (February 2006, pre-lift, lift came August 2007) and was replaced with a ford reman. Five years later at 313,900 miles, it's still going strong and pulling like there's no tomorrow. I would look into a John Wood's valve body now as it wasn't available when I added my shift kit. With the addition of the above, your trans should hold together well.
Thread Starter
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Freshman User
Joined: Jul 2011
Posts: 26
Likes: 0
Given that you tow 2-3 times a week, I'd go for the 5.13s suggested by dkf. It's a good setup for towing, as well as good power and fuel economy when you're not.
When I was lifting my truck, I did a little planning beforehand and added a few things to help my trans handle the additional load.
I added a sonnax/tricumulator shift kit and 26row 6.0 trans cooler. This helped firm up the shift and keep it cooler at the same time. My original trans went out at 127K (February 2006, pre-lift, lift came August 2007) and was replaced with a ford reman. Five years later at 313,900 miles, it's still going strong and pulling like there's no tomorrow. I would look into a John Wood's valve body now as it wasn't available when I added my shift kit. With the addition of the above, your trans should hold together well.
When I was lifting my truck, I did a little planning beforehand and added a few things to help my trans handle the additional load.
I added a sonnax/tricumulator shift kit and 26row 6.0 trans cooler. This helped firm up the shift and keep it cooler at the same time. My original trans went out at 127K (February 2006, pre-lift, lift came August 2007) and was replaced with a ford reman. Five years later at 313,900 miles, it's still going strong and pulling like there's no tomorrow. I would look into a John Wood's valve body now as it wasn't available when I added my shift kit. With the addition of the above, your trans should hold together well.
I just called randy's and the 5.13 is what they said as well. I got the gears ordered as well as ring and bearings. Cant wait to get some power back.
the guy at randy's was more than helpfull too, glad i was told about them. thanks to everyone for all the info
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