Help me understand kingpin and I-beam theory.

[guhfluh]

Is the pin a press fit in the beam or is there some play allowed? How much if so?

Is the beam reamed for kingpin fitment or is that only the spindle? As well as does the beam take bushings or only the spindle?

According to the Tech info here http://www.fordification.com/tech/Ibeamsspindles.htm there are three kingpin sizes available, but the two smaller sizes are minute in OD differences, only the length is a little different. This would have me believe that those beams can be interchanged and you'd simply use the kingpins you need for the spindles you choose. OR someone simply measured incorrectly, OR there is a wide tolerance for height between those kingpins and 0.13" doesn't matter because the end caps with grease nipple simply doesn't get screwed down as far to take up the room.

Am I off here in thinking there really are only two kingpin sizes to worry about?

I'm trying to determine my kingpin size without measuring them. I have a 67 F250 Crew Cab which is a base model, but it has 12x2.5" Bendix manual drums and evidently the larger HD I-beam bushings( I made the mistake of ordering the smaller poly bushings and they didn't fit).

[sargentrs]

The I-beam is reamed for a "slip fit" of the kingpin (about .001"-.003" over the OD of the king pin. That's in thousands of an inch) The casting of the beam is extremely hard and resistant to wear. The king pin is locked in with a notch and tapered bolt so it doesn't rotate. The spindle bushings rotate around the king pin and take the wear. They are pressed into the spindle then reamed to the same .001-.003" tolerance. The king pin slides through the bushing but won't hardly fall out on it's own the tolerance is so close. There are very thin shim washers between the spindle and the beam that keep the mating surfaces parallel so the spindle won't wobble on the beam. Then there is also a very small grease seal between the spindle and the beam too. Once you cap off the king pin with the grease caps, and pump it full, the grease actually fills up the remaining space between the king pin and the spindle making a tight pivoting joint with no play to it. The complete assembly is matched in length and diameter so there's little if any interchangeability between the different lengths and diameters which is why on '73-'74 spindles are interchangeable with bump I-beams that use identical king pins.

[elgemcdlf]

Wow Randy. I did years doing suspension and brake work. I did more king pin jobs that I can remember. I bought a .5" air chisel just for driving stubborn pins out. I couldn't have laid it out any better sir. My hat is off to you.

[guhfluh]

I agree that was great. Thank you!

So, in theory though, could beams and spindles that use the smaller kingpins be machined for the larger kingpins? With the kingpin being centered, does the roughly 0.065" max length difference on one end make that much of a difference?

Where I'm going with this is DJM suspension only offers one beam for all years. AIM offers only two different kingpin sizes and their differences is in OD only. If i order some beams, I want to know my stuff so I can hold them accountable if there are any problems and make sure I order the right stuff.

[sargentrs]

Wow Randy. I did years doing suspension and brake work. I did more king pin jobs that I can remember. I bought a .5" air chisel just for driving stubborn pins out. I couldn't have laid it out any better sir. My hat is off to you.

Aw shucks. You're gonna make me blush. Never done it before myself, just made sense

[sargentrs]

IMO, the deciding factor is, if the diameter is the same, would be the location of the notch in the king pin. That would determine where the king pin locates in the spindle which could throw the whole difference in length one direction or the other. I know .065" doesn't sound like much but 1/16" could be the difference between putting a grease cap on or not as they only have a couple of threads on them and you really need that cap to fit tightly to contain the grease and take up the tolerance or you'll just wear the bushings out prematurely. And, in addition, if that notch in the king pin does not center the length between the top and bottom bushing you may not be able to get a cap on at all and the pin could only reach part way into the bushing. Lot of things to consider. Many people have used the drop beams and I believe they used the stock king pins, pretty much just plug n play. Maybe somebody whose actually installed them will chime in with their experience.