3rd member swap
Thread Starter
|
Senior User
Joined: Oct 2004
Posts: 100
Likes: 0
From: Maggie Valley, NC
3rd member swap
Hey yall...got a couple of questions...I have a 71 F-100 with a 9". My friend has a 78 or 79 with a 9" also. I have 4.11 gears and he has 3.55's. Can we just swap our 3rd members? Also, will this affect the speedo?
Senior User
Joined: Nov 2002
Posts: 375
Likes: 0
maybe he's concerned with width and spring perch location so that they can just swap out the whole rear end......I'm interested in that so that I can get the whole thing from the junk yard....also which years are more likely to have 31 spline axles.....if your are counting splines on the axle you count the valleys not the peaks right....?
and yes that much of a gear change will effect speedo accuracy....but I don't know what size tires you are using....
and yes that much of a gear change will effect speedo accuracy....but I don't know what size tires you are using....
5th Wheeling
Joined: Mar 2005
Posts: 39
Likes: 0
Originally Posted by zsir
maybe he's concerned with width and spring perch location so that they can just swap out the whole rear end......I'm interested in that so that I can get the whole thing from the junk yard....also which years are more likely to have 31 spline axles.....if your are counting splines on the axle you count the valleys not the peaks right....?
I don't believe any of the 67-72 trucks have 31 spline axles.
Posting Guru
Joined: Mar 2004
Posts: 1,099
Likes: 0
From: Destin/Ft. Walton Beach,
I don't believe any of the 67-72 trucks have 31 spline axles.
!["Beemer Nut"'s Avatar](data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 50 50'><circle class='avatar-circle-default' fill='%23bc5285' cx='25px' cy='25px' r='20px'></circle><text class='avatar-text-default' x='49%' y='53%' fill='white' text-anchor='middle' alignment-baseline='middle'>"</text></svg>)
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
Trending Topics
Laughing Gas
Joined: Aug 2004
Posts: 964
Likes: 1
From: Roseburg, OR
We're talking about the 9" though, right?
I have heard that SOME '72 F-100s actually had 31 spline shafts, and indeed, the trashed 3rd member that came in my truck (admittedly, on the passenger side floorboard...) had 31-spline side gears and bearings. The truck had 28-spline axle shafts with it, however, so I don't really know what it had from the factory.
I have heard that SOME '72 F-100s actually had 31 spline shafts, and indeed, the trashed 3rd member that came in my truck (admittedly, on the passenger side floorboard...) had 31-spline side gears and bearings. The truck had 28-spline axle shafts with it, however, so I don't really know what it had from the factory.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 6 Best Deals Available on New Fords & Lincolns Right Now
Brett Foote
This Hennessey Takes the Expedition Tremor's Off-Roading Capability to the Next Level
Verdad Gallardo
Top 10 Fords at 2026 Carlisle Ford Nationals
Joe Kucinski
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
Originally Posted by 1bad71F100
Hey yall...got a couple of questions...I have a 71 F-100 with a 9". My friend has a 78 or 79 with a 9" also. I have 4.11 gears and he has 3.55's. Can we just swap our 3rd members? Also, will this affect the speedo?
Yes changing rear ratios will affect the speedo reading.
John
