Rear end interchange
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Senior User
Joined: Jun 2005
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From: Temple, TX
Rear end interchange
This could be a dumb question, but if I wanted to find a 9" rear end from a junk yard to replace my existing one, would it have to come from a 73-79 truck, or do the earlier/later generations have the same axle width as well?
Thanks
Thanks
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Senior User
Joined: Jun 2005
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From: Temple, TX
Summit lists the same axle shafts for '75 through '86 trucks and vans, so I assume any 9" from one of those vehicles will fit? I can look up the codes on the tag to make sure it's a 31 spline. Hopefully tomorrow I can find myself a 4.11 rear end to swap in 
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From: Skyway, WA
I think the donor for my my current 9inch third member came out of a 67-72 era truck. I was cautioned at the time to make sure whatever I got had 28 splines as my axles were 28 spline. There are 28 spline and 31 spline varieties. I think I nearly ruined my shoulders sitting cross legged under my truck and lifting the third member onto the axle housing studs. I was younger then, wouldn't do it today
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Senior User
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From: Temple, TX
That heavy, huh? I'm actually looking at swapping the entire rear end, not just the third member. My current housing seems to be leaking fluid from one of the welds in the rear, which makes me think it wouldn't last too long at the drag strip.
Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
1973 and later 9's have a wider axle housing than was used 1957/72.
The frame rails behind the cab are not the same width after 1972.
1957/72: The width between the rear frame rails is 33 1/2"
1973 and later, the width is 37 1/2 inches.
The FoMoCo AXLE ID tag bolted to the carrier does not have the spline count listed.
However...if there is no tag, the only way to find out if the shafts have 28 or 31 splines is to pull the axleshaft.
Makes no sense? The tag has a code which when decoded lists the rear axle parts list in the parts catalog. From there, the spline count can be found out.
This is the only way to discover whether it has 28 or 31 splined axleshafts without pulling the axles.
After 1973, there are two different rear axle seals.
1975/86 9 inch axle shafts are NOT all the same, regardless of the spline count!
The frame rails behind the cab are not the same width after 1972.
1957/72: The width between the rear frame rails is 33 1/2"
1973 and later, the width is 37 1/2 inches.
The FoMoCo AXLE ID tag bolted to the carrier does not have the spline count listed.
However...if there is no tag, the only way to find out if the shafts have 28 or 31 splines is to pull the axleshaft.
Makes no sense? The tag has a code which when decoded lists the rear axle parts list in the parts catalog. From there, the spline count can be found out.
This is the only way to discover whether it has 28 or 31 splined axleshafts without pulling the axles.
After 1973, there are two different rear axle seals.
1975/86 9 inch axle shafts are NOT all the same, regardless of the spline count!
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Senior User
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From: Temple, TX
Makes sense. I didn't know if my current axles were 28 or 31 spline until I looked up the tag info, since the previous owner had swapped the rear end in from another truck.
If the axle shafts are not all the same, is there some listing where I can find out which vehicles I can ****** a rear end from that will work with my truck? Just '73 to '79s?
If the axle shafts are not all the same, is there some listing where I can find out which vehicles I can ****** a rear end from that will work with my truck? Just '73 to '79s?
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Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
Makes sense. I didn't know if my current axles were 28 or 31 spline until I looked up the tag info, since the previous owner had swapped the rear end in from another truck.
If the axle shafts are not all the same, is there some listing where I can find out which vehicles I can ****** a rear end from that will work with my truck? Just '73 to '79s?
If the axle shafts are not all the same, is there some listing where I can find out which vehicles I can ****** a rear end from that will work with my truck? Just '73 to '79s?
Let's say the code is WDM-A. That decodes to parts list #91. Then the parts list shows the specific axleshaft that fits WDM-A.
The next step is take the axleshaft part number to the axle specification chart to see how many splines the axleshaft has.
As you can see, this is a lotta monkey motion, but this is the way Ford does things, and is the only way I can help you.
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Senior User
Joined: Jun 2005
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From: Temple, TX
I understand how to look up the axle tag codes 
I guess what I'm trying to ask is, if I find an axle out of any '73 or newer truck, and I determine that it is 31 spline, does that mean it will work for what I'm trying to do, or is there another variable there? If I find one out of, say, an '82 truck, look up the tag info and discover that it is a 31 spline, would that work?
Thanks for the help
I guess what I'm trying to ask is, if I find an axle out of any '73 or newer truck, and I determine that it is 31 spline, does that mean it will work for what I'm trying to do, or is there another variable there? If I find one out of, say, an '82 truck, look up the tag info and discover that it is a 31 spline, would that work?
Thanks for the help