Rearend Swap
Junior User
Joined: Jun 2014
Posts: 51
Likes: 0
Your best bet is to decide what ratio you need. If it's just a wholesale increase in MPG and your not too worried about performance, then something in the low 3's should fit the bill. From 3.07:1 to 3.42:1. Pull the center section from the rearend housing and take it to a trans shop or a local mechanic that can swap out the ring and pinion gear for you. It's not something you want to do yourself without any prior knowledge. While you have it out, I'd have new selas and axle bearings installed on the axle shafts.
Elder User
Joined: Feb 2014
Posts: 713
Likes: 3
From: Florida
First of all, when you find a complete axle out of a different truck, is the axle you found in excellent operating condition? You could go through a lot of work to find out you bought a crap used axle....If you have a 9" rear you are already fortunate as this was a great design that allowed removal of the entire ring and pinion final drive assembly ("the chunk") so you can change and set up the ring and pinion on the bench. I used to enjoy working on these. Have you even considered what final ratio you really want other than 4:10 to suit your needs? 3:73 or 3:56 or ??? If you have a 351W with an automatic trans, the money you spend to swap out your rear would be better spent on gasoline IMO. I doubt you will gain any significant fuel economy by altering the rear diff because you will be pressing on the gas pedal more to move the truck as easy as it does now with the 4:10 ratio....
Posting Guru
Joined: Nov 2008
Posts: 1,255
Likes: 2
From: Santa Monica, CA
What size are your rear tires? You said the trans is an AOD, right? Plug your numbers into this calculator and see what rpms you're running with your current setup. If your rear tires are too short, you might be able to accomplish some improvement by simply running taller tires......just a thought...
http://www.ringpinion.com/Calculators/Calc_RPM.aspx
http://www.ringpinion.com/Calculators/Calc_RPM.aspx
Senior User
Joined: Jul 2014
Posts: 307
Likes: 0
From: Northern California
9" rear from info
This article is very useful about the 9" rears.
Hemming's Motor News: Ford 9-inch differentials | Hemmings Motor News
There is also a lot of info on the Mustang sites also.
Hope this helps.
Hemming's Motor News: Ford 9-inch differentials | Hemmings Motor News
There is also a lot of info on the Mustang sites also.
Hope this helps.
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REBELboy_327
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
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May 24, 2005 08:57 PM
