Kingpins, because that's what I'm researching right now.
But first ...
I really, really, really try to avoid assuming someone knows the jargon and fundamentals associated with a particular topic. So, I prefer to cover the basics before launching into a more in-depth discussion. In particular, some people are hesitant to reveal they don't know something and get lost because they don't ask for an explanation of something unfamiliar to them.
Also, a bit of history often helps people (and me) understand how we got where we are.
So ...
Kingpins equal Ball joints. They both perform the same function.
Kingpins predate motorized vehicles. In the early days of automobiles and trucks, everything used kingpins. At some point in time automobiles and some light trucks switched to ball joints instead of kingpins. My daughter's Plymouth Savoy has ball joints so I know the change occurred prior to 1959. (Readers are welcome to try to determine when the industry started switching to ball joints.)
Most trucks continued using kingpins well into the 90's. My 1990 Ford E-150 (1/2-ton) van uses kingpins. Newer light trucks may have switched to ball joints ... I don't know because, as far as I'm concerned, older is generally preferable.
Solid axles almost always use king pins, as well as most older trucks with IFS (independent front suspension), like my 1990 E-150. I believe, however, IFS technology contributed to the change to ball joints.
Heavier duty trucks continue to use kingpins because kingpins are able to handle greater stresses than ball joints.
Ball joints are common so information on them, and people to work on them, is readily available. Kingpins are becoming increasingly less common, so the reverse is true. (Try googling kingpins ... most of the returns will be about bowling or the illegal drug trade.)
Worn kingpins, as with worn ball joints, make a vehicle hard to control and make it impossible to properly align the suspension.
When someone talks about replacing the kingpins, they're actually talking about replacing the bushings. The kingpins themselves rarely, if ever, wear out. (The kingpins out of my '73 RM350 chassis are good as new.) However, most (all?) kingpin replacement sets include the kingpins, in addition to bushing and associated hardware. All sets include kingpins, bushings, etc., for both sides of an axle because, as with brakes and bearings, you should do both sides of an axle at the same time.
I have indications it may be possible to purchase individual components (bushing or hardware) but it's more convenient and probably cheaper to just get a set.
There's two types of bushings used with kingpins: plastic (usually Delrin -- a brand name -- or something similar) and metallic (usually bronze).
Plastic bushings are easier to install and are usually pre-sized, eliminating the need to have them reamed. My 1990 E-150 came with plastic bushings and I believe most manufacturers install plastic bushings as OEM equipment.
However, the same characteristics that make them easier to install make them more inclined to wear out and less able to withstand stresses.
Close tolerances between the kingpins and bushings is important to vehicle handling. (Tolerances increase as the bushing wears out, which is why bushings need to be replaced.) Pre-sized bushings are made with greater tolerances to account for manufacturing variances. So, pre-sized bushings are effectively "partially worn out" when new.
Some information on the web indicates replacement sets with pre-sized bushings are available for some 1/2-ton and a few 3/4-ton trucks. Even if these bushings are metallic, the previous paragraph still holds true with regard to tolerances.
Aside, while I'm thinking of it: The proper way to grease kingpins is to jack up the front of the vehicle to take stress off the kingpins, allowing the grease to flow around the kingpin better. (I didn't know this until recently.)
Obviously, metallic bushing that require reaming are better. They resist wear better, can handle more stress, and can be reamed to much closer tolerances. (Assuming the person installing them know what they're doing, have necessary training and experience, and are willing to take the time to do the job correctly.)
The downside is the metallic replacement sets tend to cost more due to economy of scale. More plastic sets are sold because most shops and mechanics prefer them because they're easier and faster to install.
This is assuming you can find a shop or mechanic to do the work. I've received reports of some shops saying, "What are kingpins?"
The real expense is in the reaming. Done properly, it's a slow, tedious, painstaking process. So, quotes of a hundred or more is not uncommon. However, I suspect some of those quotes are based on the shop having to buy the necessary tools. (If they have to buy the tools, I doubt they have the experience to do it properly.) From what I can tell, an experienced mechanic should be able to complete the reaming in a half hour or less. (I expect to spend an hour or more because I've never done it before and will take the time to do it carefully.)
Enough for now ... in a soon-to-come post I will discuss how to cut your costs and how to possibly do the job yourself.
