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You are here: Home Tech Articles & Tutorials Steering / Suspension / Brakes Comparing I-beams and Spindles
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Comparing I-beams and Spindles

ALSO SEE: Steering/Suspension Component Variations

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 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.)

Fig. 3 - Here is the '67-only setup. A raised pad on the I-beam contains a stop rod which contacts the bump stop on the spindle.

Fig. 4 - Here's the drum-brake spindle and I-beam used on '68-up trucks.

Everything else checked out as identical, for the most part, aside from some minor cosmetic differences. The kingpin retainer is in the same position on each but there is a slight difference in kingpin length and diameter. The difference in diameter of the '67-'74 vs. the '75-'79 kingpins is only .0001" which could easily be compensated for by the machine shop who reams the kingpin bushings...however, I'm not sure whether the difference in kingpin height would cause a problem.  Therefore, it's best to only swap the I-beam and spindles as a set and then order kingpins for the year matching your I-beams and spindles.

Mating a '73-'74 I-beam with a '68-'72 spindle will work just fine, since the later spindle's bump stop simply contacts the I-beam at it's limit, just like the early versions, and the kingpin diameter and height is the same. However, mating a '75-'79 spindle with a '68-'74 I-beam means the shorter bump stop on the spindle will have to travel further than it's designed to, because of the lack of an I-beam receiving pad. And that's in addition to the differences in kingpin diameter and height.

Bottom line: if you're swapping on later model hardware, it's best to swap the I-beam and spindle as a unit. If you MUST mix and match, follow these simple guidelines:

  • If you're using '75-'79 spindles, use '75-'79 I-beams and kingpins

  • If you're using '68-'74 spindles, use '68-'74 I-beams and kingpins

  • If you're using '67 I-beams, use '73-'74 spindles and kingpins. However, the round pin used for the bump stop in the '67 I-beam may need to be trimmed or modified, as needed.

King Pin dia. (in.) Application Notes
.8592" x 6.353" 1967-1974 1/2-ton -
1967-1970 3/4-ton


1971 3/4-ton 3000-lb axle - 12 1/8" x 2" drum brakes - from serial #M00,001
1972-1974 3/4-ton 6200-lb GVW exc. Super or Crew Cab
.8593" x 6.483" 1971 3/4-ton 3000-lb axle - disc brakes or 12 1/8" x 2" drum brakes - thru serial #M00,000 OR 12" x 2 1/2" drum brakes
1975-1979 1/2-ton


1972-1974 3/4-ton 6900-lb GVW - w/o 460 engine exc. Super or Crew Cab
1975-1979 3/4-ton 6200-6900-lb GVW
1.0540" x 6.450" 1971 3/4-ton 3500-lb axle
1972-1973 3/4-ton 7500-8100-lb GVW axle
1973-1974 3/4-ton 6900-lb GVW axle w/460 engine or 7500-8100-lb GVW axle
1975-1979 3/4-ton Super or Crew Cab or 7900-8100-lb GVW axle
1967-1979 1-ton


Here are some other related observations:

Fig. 5 - Here is a comparison of the '79 dust shield (left) vs. the '74 dust shield. The later version has a built-in air scoop for better cooling.

I probably should have cleaned this one up a little for this shot, but I was feeling lazy. I'm just including it for the visual. This is the front disc brake setup for a '75 F-250. Note the spindle is completely different from the F-100 version, and the 'extra cooling' of the vented dust shield.


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