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How do I know if I have 3.55 or 3.73?

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Old 05-21-2013, 09:22 AM   #1
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Default How do I know if I have 3.55 or 3.73?

When I had my truck built it was listed as having a 3.55 rear axle. I changed the order to get the 3.73. How do I know for sure that this happened besides the dealer telling me it did. Is there anything to look at underneath or in the manual to reflect this. Any help would be appreciated.
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Old 05-21-2013, 09:49 AM   #2
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The label on the door will show the axle code.
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Old 05-21-2013, 10:44 AM   #3
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Should also say on the window sticker.
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Old 05-21-2013, 12:16 PM   #4
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worst case should be a metal tag attached to a cover bolt
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Old 05-21-2013, 01:31 PM   #5
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Hey NewFX,

My '13 has the 3.73 as well.

What is the difference? Advantages/disadvantages?

Thx.
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Old 05-21-2013, 04:26 PM   #6
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Take a look at the below chart, it lists all of the available axle codes and tells you where to look for the sticker with this info.
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How do I know if I have 3.55 or 3.73?-axlecode.jpg  
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Old 05-21-2013, 04:41 PM   #7
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lets put it this way also
if your rear gears dont match the front you have bigger issues when you switch to 4wd

raise up the rear on a jack ... take chalk.. mark the side of the tire
and the side of the driveshaft
turn the tire as you lay on the ground and watch to see how many times the shaft turns
if its almost 4 (3.73)
if its about 3.5 its 3.55's

thats easiest way to know
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Old 05-21-2013, 08:37 PM   #8
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Actually the easiest way is to plug your VIN# into the box on this link, http://www.f150forum.com/vindecoder.php that will tell you a lot about your truck, axle ratio being one.



EDIT: Never mind, that's one thing it wont tell you, strange.

Last edited by Rnlcomp; 05-21-2013 at 08:42 PM.
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Old 05-22-2013, 10:43 AM   #9
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Quote:
Originally Posted by Adverse FX View Post
Hey NewFX,

My '13 has the 3.73 as well.

What is the difference? Advantages/disadvantages?

Thx.
Nut shell 3.73 makes it easier to tow off the line than the 3.55. Off the line you get better towing with a high ratio number. This provides the truck more low speed wheel torque and makes it easier to get the vehicle moving. Minor gas milage difference to the worse but you would never notice.
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Old 05-22-2013, 06:23 PM   #10
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Quote:
Originally Posted by 13f150plat View Post
lets put it this way also
if your rear gears dont match the front you have bigger issues when you switch to 4wd

raise up the rear on a jack ... take chalk.. mark the side of the tire
and the side of the driveshaft
turn the tire as you lay on the ground and watch to see how many times the shaft turns
if its almost 4 (3.73)
if its about 3.5 its 3.55's

thats easiest way to know

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