1968/78 steering box issues
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3rd Gear
Joined: Mar 2025
Posts: 3
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From: South Carolina
1968/78 steering box issues
Hey guys. First time posting in this forum. I have a 68 F100 that I am doing an '05 super duty axle swap on as part of a full rebuild. I've got a 78 4WD F250 steering box that I am using since I want power steering/a heavier duty steering box. The issue I am having is that the input shaft for the box is 0.72" x 35 spline (with a single master spline) instead of the common 3/4"x36 spline input shaft type. I can't find a universal joint or rag joint anywhere with the smaller 0.72" shaft diameter. I tried a 3/4"x36 spline ujoint but it has too much slop for my liking. I have the ability to fab an adapter if I could find anything with that spline pattern, but I can't seem to find anything. Is this a normal issue and is the solution just use a 3/4"x36 and tighten down the set screw?
Hotshot
Joined: Feb 2004
Posts: 10,785
Likes: 2,595
From: The Shenandoah Valley
What I have done, and what I'd do again if needed, is take the portion of a coupler that fit my steering box shaft, and the portion of a coupler that fit my steering shaft, meld them, hold my tongue just right, and create an adapter. Not like that shaft or coupler will see great force.
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3rd Gear
Joined: Mar 2025
Posts: 3
Likes: 1
From: South Carolina
That was my thought when I wasn't able to find a ujoint with the correct splint pattern, but I couldn't find anything with the 0.72" diameter...at least nothing that said it was that diameter in the specs. From my research it looks like it was only boxes on the 4WD 250s that had the smaller diameter. I guess I just buy and OEM rag joint for a 4WD 78 250 and hope it is the 0.72 diameter instead of 0.75?
Moderator & parts slinger
Joined: Feb 2007
Posts: 50,157
Likes: 5,786
From: S/W Missouri, Polk county
Flaming River. https://www.flamingriver.com/steering-universal-joints
Borgeson. https://www.borgeson.com/Universal-Joints/
I am sure one of the above companies should have the correct spline u joint, or the 2 below.
Speedway and Summit racing might be a good place to look, if you have not.
Borgeson. https://www.borgeson.com/Universal-Joints/
I am sure one of the above companies should have the correct spline u joint, or the 2 below.
Speedway and Summit racing might be a good place to look, if you have not.
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3rd Gear
Joined: Mar 2025
Posts: 3
Likes: 1
From: South Carolina
Yeah, I looked at those and many more. I called Borgeson and nobody there had heard of the smaller diameter shaft. They said 0.72 was within spec for a 3/4x36 spline shaft. It sounds like ford might have just undersized them to make assembly easier and still used the 3/4" rag joint. I'm going to try using some shim stock to tighten up the joint and then run some green or blue loctite on the set screw to keep it from backing off. Probably put some leverage on the steering wheel to make sure the joint withstands some torque.
Moderator & parts slinger
Joined: Feb 2007
Posts: 50,157
Likes: 5,786
From: S/W Missouri, Polk county
Don't stick a piece of pipe through there and get all crazy with the torque, think seat belt that has jerk locked into place to hold it. Because you can crack a steering wheel.
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