While getting ready to
rebuild the '79 F100 disc brake front-end that was
installed onto my '67, I started checking for some new brake rotors, and
noticed that all the parts catalogs had a cutoff between 1965-74 and 1975-79.
This seemed to infer that there was a difference in hardware between
those two eras. Then, at the FORDification forums, somebody asked
whether a '79 I-beam would fit onto a '67 spindle, so I decided to do
some research into this area...to discover the differences between the
various years of I-beams and spindles.
After spending an
entire afternoon comparing the front end pieces from a '67, '68, '74 and
'79 F-100s and a '75 F-250, I have discovered some of the main areas of
discrepancy. The two '60s-era pickup front-ends that I used for reference
were set up for drum brakes, and the '70s-era versions were all disc. The
'79 setup was disassembled completely for powdercoating, but the others
were either still installed, or removed as an assembly.
The biggest two differences
between the '74-earlier vs. the '75-later units is in the area of the
steering bump stop and kingpin diameter and height. In Fig. 1, you can see the '74 version of the bump
stop. That is the large protrusion from the spindle that simply contacts
the I-beam when it's at it's steering limit. You can see that there is
nothing on the I-beam which contributes to the bump stop limits, like a
receiving pad. The spindle for the '79 has a shorter bump stop, but the
difference in size is compensated for by a receiving pad cast into the
I-beam, as seen in Fig. 2.
Fig. 1 - Pre-'75 spindles had the
steering bump stop cast into itself with no receiving pad on the I-beam.
Fig. 2 - The '79 I-beam has a receiving pad cast into it, which is
contacted by the shorter bump stop on the spindle. (I mislabeled it as a
'78 in this pic.)