The automobile evolved from the wagon and some cars and trucks used wagon type I-beam front axles until the early postwar years. Each wheel spindle typically has a yoke attached to it that fits over one end of the axle. The upper and lower ends of the yoke and the end of the axle are drilled so that a pin can be pushed through the holes. This king pin has a flat spot that allows it to be held in one position by a stake or bolt, so that it remains stationary once in place. Then the spindle can be swung back and forth on its yoke to allow steering.
The British call king pins "swivel pins," a term that actually describes their function more clearly. Whatever you call them, they need to be lubricated to prevent rapid wear and they need to be fitted just right so they swing smoothly. Lubrication of pins is accomplished by drilling holes in the yokes that are threaded on their upper (outside) end to accept a grease fitting.
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To give proper fit, bushings are inserted into each "branch" of the yokes and reamed to the right size opening. A too-tight pin would cause steering members to bind and a too-loose pin would cause vibration. The bushings also have holes drilled in them that line up with the lubrication holes in the yokes, so the grease gets all the way to the pins instead of being blocked by the bushing. There are some cars that left the factory with the king pins riding on needle bearings, rather than bushings, but these were usually repaired with bushings.
Before final installation of the pins, thrust washers with shims are placed at the bottom of each end of the axle, so that the pin goes through them before entering the hole in the yoke. These act as bearings so that the spindles swivel more smoothly. The shims are used to keep the up and down movements of the assembly within specs. Oil sealing plugs are also inserted at the top and bottom of the pins to keep oil in the spindle. These are staked in place with a punch.
In this article, we are going to discuss removing a beam axle from a 1940 Dodge pickup, breaking it down to component parts and the installation of king pin bushings. For veteran old car restorers, this is nuts-and-bolts stuff, but for the beginner or the mechanic with only modern car training, there's a definite learning curve. We read countless discussions of king pin bushing fitting on a popular hot rodding bulletin board and they were confusing. One poster would recommend using a machine shop to ream the bushings and the next would warn that his machine shop botched the job and say hand reaming was easy.
Another eye opener was a trip to the local parts store to see if they sold a king pin reaming tool. After initially answering the question with a blank look, the counterman called his warehouse and discovered there were two versions of such equipment available. One was $2,600 and the other was $5,600! We're guessing that the second quote included a hydraulic press that could push the bushings into the yokes. The first was probably for a set of hand reamers, because a commercial installer would need a set of different sized reaming tools to carry a variety of applications. There's no one-size-fits-all option here.
We were able to take the axle apart, push the old bushings out, put the new bushing in and hand-ream the bushings using equipment that we had on hand in our small shop, along with borrowing the proper size reaming tool from a very well-equipped mechanic who helps us a lot. We also found vintage reaming tools available on eBay at prices between $30 and $60, as well as a new one that Speedway Motors (www.speedwaymotors.com) makes for midget racing cars. The important thing with these tools is the size, not the specific application they were made for. Measure the diameter of your pins and look for a tool that can ream the bushing out to just a tad over that size. We have not run across a general spec for reaming. Apparently, mechanics of the day knew the right "feel," which is could be described with "as tight as possible with no binding."
As we said, taking the axle off the truck was a nuts-and-bolts operation, but some of those fasteners were huge. The fact that they may not have been loosened since 1940 didn't help either. We used a giant ratchet wrench set that we bought at Harbor Freight. It did the job, but we made a mistake using the ratcheting drive, because its bearings were not up to the job and we ruined it. We would have done fine if we used only the bar and the sockets.
The job starts by raising the front end of the truck. This was easy, as we were working with the stripped frame. With the rails supported on stand jacks, we took off the hubcaps, wheels and tires. Each end of the front axle was bolted to the frame with four heavy bolts. With these removed that axle came off the frame as a unit. Since the hubs, brake backing plates, brakes, bearings, yokes, spindles and steering linkage parts are all still attached, you have a heavy unit.
Removing four bolts on each side allows removal of front axle from frame.