Ford 9" compatability
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Senior User
Joined: Jan 2003
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From: Calgary
Ford 9" compatability
The 9" rear end in my '72 F100 has 3:25 gears and I want to change to something numerically higher. If I go to the wreckers and look for a new center section, what compatability issues do I have to be aware of? Is the spline count always the same? What years would fit my truck?
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Post Fiend
Joined: Mar 2002
Posts: 19,402
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From: Bonita Springs FL
The mustang 9" axles usually have 28 splines. Pickups normally came with 31 spline axles. However, Ford loved to use up parts that it had laying around, and who knows what a previous owner did to a vehicle before it went to the boneyard. The only way to know for sure is to pull the axle and count the splines on the shaft.
Cargo Master
Joined: Dec 2003
Posts: 2,735
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From: Sunny Florida
You can chage a 31 spline to a 28 but you can not change a 28 spline carrier to 31 spline axles because the axle hole in the carrier is to small on the 28 spline to accept 31 spline axles.
You can swap the complete carrier if you wish to change the ring gear.
Be careful not all ford trucks came with 31 spline axles. F100 will more than likely have 28 and I have found both 28 and 31 in vans. It's best to make sure what you have before going out an buying another third member. Any 9 inch third memeber will bolt right in as long as the axle spline matches.
You can swap the complete carrier if you wish to change the ring gear.
Be careful not all ford trucks came with 31 spline axles. F100 will more than likely have 28 and I have found both 28 and 31 in vans. It's best to make sure what you have before going out an buying another third member. Any 9 inch third memeber will bolt right in as long as the axle spline matches.
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Senior User
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From: Calgary
OK I took your advise and pulled one of my axles out to see the splice count. I have 28 splines.
I went to the local pick-a-part and started looking. What I would like to find is a 3.50 or 3.73 to replace my 3.25. There were lots of 3.00s and a few 3.50s but they were all 31 splines. The bearings on the 31 spline rears are the, much beafier looking tappered roller type vs what I have which looks like a ball bearing.
My truck is a 72 and the rear end is narrower than the later trucks. Now I am thinking maybe I should swap a whole rear end that would give me the right ratio and also a bit wider stance in the back. Quite a few trucks I looked at had anti-roll bars at the back so that might be a good thing to add too.
Comments?
I went to the local pick-a-part and started looking. What I would like to find is a 3.50 or 3.73 to replace my 3.25. There were lots of 3.00s and a few 3.50s but they were all 31 splines. The bearings on the 31 spline rears are the, much beafier looking tappered roller type vs what I have which looks like a ball bearing.
My truck is a 72 and the rear end is narrower than the later trucks. Now I am thinking maybe I should swap a whole rear end that would give me the right ratio and also a bit wider stance in the back. Quite a few trucks I looked at had anti-roll bars at the back so that might be a good thing to add too.
Comments?
Cargo Master
Joined: Dec 2003
Posts: 2,735
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From: Sunny Florida
You can swap the complete rear axle or just swap the side gears in the carrier if it's an open carrier to open carrier or trac loc to trac loc. This would take a little work like reseting the back lash. I would just swap the complete rear axle.
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Senior User
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From: Calgary
So are the side gears different on a limited slip diff. than and open one? The reason I ask is in case I find a LS diff at the junk yard...can I use it in my '72.
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Cargo Master
Joined: Dec 2003
Posts: 2,735
Likes: 38
From: Sunny Florida
The trac loc has different side gears/spider gears and can not be swapped with an open carrier. I have all the parts needed to swap a 31 spline trac loc over to a 28 spline set up so PM if you end up needing them.
You will only find a 28 spline trac loc in the older ford full size cars and even then they have the wrong gear ratio. It would be lower than your 3.25 and you want a higher gear ratio.
The 3.25 ratio you have may have some good value to it if you leave it set up and not pull the carrier from. The early mustang guys are always looking for 3.25 and 3.50 gears but 99% of what shows up is 31 spline and they need 28 spline set ups.
If you do swap rear axles measure the leaf spring pad width to make sure it's the same.
You will only find a 28 spline trac loc in the older ford full size cars and even then they have the wrong gear ratio. It would be lower than your 3.25 and you want a higher gear ratio.
The 3.25 ratio you have may have some good value to it if you leave it set up and not pull the carrier from. The early mustang guys are always looking for 3.25 and 3.50 gears but 99% of what shows up is 31 spline and they need 28 spline set ups.
If you do swap rear axles measure the leaf spring pad width to make sure it's the same.
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