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Fitment Guide for 1967-1979 F100 / F150 2wd to 05+ SD axle kit

Half ton 2wd frames are very similar to F250 2wd frames. The main difference as far as this swap goes is the portion of the frame rail that accepts a radius arm bracket


Here is a quick summary of what you need to know:
-1973-79 F250 2wd trucks seem to have 5 oem holes roughly 16" behind the front cab mount. These are for a perch that suports the transmission crossmember. Only 2 or 3 holes are actually used in any given application. Radius arm brackets bolt to these holes.

-1973-1976 trucks mostly need my part number "F15b" which has a tighter grouping of these 5 holes but it is not unusual to have a different (or no) hole pattern

-1977-1979 trucks mostly need my part number "F15a" which has a further spaced grouping of these 5 holes.

-1967-1972 (and some later) trucks mostly need my part number "F15c" and do not have any of these 5 holes, but instead the transmission crossmember bolts to the bottom flange of the frame with a single vertical bolt per side.

-Supercabs: Be cautious ordering if you have an F250 supercab. The main thing to look for is the contour of the bottom of the frame rail at the area of the radius arm bracket. Some Supercabs need a flat bracket, some need a bracket with two bends.
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Where to look
Pictures and measurements based off of driver side transmission cross member rivets and holes about 12" to 16" behind the forward cab mount
 
















Most all trucks seem to have a combination of 6" spaced pair of holes and 5 5/8" spaced pair of holes. Some trucks have these pairs of holes spaced differently relative to each other.
Below shows these pairs of holes and you can see that this particular truck only used the 5 5/8" spaced holes. It does not matter which set your truck uses.
 
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F15a:
1. The distance from first hole to second hole will be 1.8" +/- .1".

2. The distance from the rear flange of the front cab mount to the front of the 6" spaced holes will be 11 5/8" +/- .1".

3. The distance from the bottom of the frame to the center of the rear of the 6" spaced holes will be 2.25" +/- .1". there seems to be a decent amount of variance in this, that's nothing to get worried about- except if you have a supercab double check that you dont have an "x15" frame shown below
4. The bottom of the frame is fairly flat
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Below is how I am measuring for that 11 5/8" measurement
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F15b:
1. The distance from first hole to second hole will be 0.8" +/- .1".

2. The distance from the rear flange of the front cab mount to the front of the 6" spaced holes will be 12.2" +/- .1".

3. The distance from the bottom of the frame to the center of the rear of the 6" spaced holes will be 2.25" +/- .1". there seems to be a decent amount of variance in this, that's nothing to get worried about.
4. The bottom of the frame is fairly flat
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F15c:
1. There are no holes drilled to support the transmission crossmember on the vertical part of the frame. The holes pictured above simply don't exist on these trucks. The transmission crossmembers are held in by a single vertical bolt per side through the bottom flange of the frame. These holes are in inconsistent locations so I make a bracket that has a slotted hole to accommodate likely all possible oem transmission crossmeber bolt holes.
 
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X15A / X15B:
This frame has the same 5 hole pattern as either F15a or F15b shown above, however the frame rail expands into a taller rail, and there is more space from the bottom of the frame to these holes. You can see a curve in the bottom of the frame.
1. The A and B spacing is the same of F15A or F15B above
.
2.
The distance from the bottom of the frame to the center of the rearmost of the 5 holes will be 3" +/- .25".
3. The bottom of the frame is not flat like F15 frames shown above and requires a bracket with two bends 
 
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