Back before ball joints, cars were made with upper and lower control arms, and 3 hinges. The steering axis was a big hinge called the kingpin (carried over from the days of solid axles), and the upper and lower control arms connected to the steering knuckle/hub assembly at two hinges at the outer ends of the two control arms. That construction required the inboard control arm pivot axes to be parallel, so anti-dive geometry wasn't possible. Kingpins went out of style in about 1960, but my 1970 Datsun still had them. Datsun engineering in those days was partly a holdover from Datsun having licensed the British Austin 7. Some of these parts have a little residual Austin DNA.

I wanted to check out the condition of the upper and lower pivots, so the first step is releasing the torsion bars. The torsion is on the lower arm, and the stop is on the top arm, so the link between them is in tension until these bolts are removed

Next step is to remove the brakes and the hub.

Did you know Datsun 521 front wheel bearings are totally unavailable? Apparently they weren't dimensioned to fit anything else on earth. Incredible.

Even more incredible stuff: Datsun front drum brakes are uni-directional. The piston is seen here from the front, where the moving part is. In the back, there is no piston. When the truck is rolling backward down a hill, you don't have any front brakes. If you get it moving backward fast enough (i.e. down a hill) this truck will do Jim Rockford turns for the ages.

The backing plates have a keeper on the bottom, but have nylon insert nuts on the top. Datsun used cad-plated fine thread english-sized hardware on everything. It's very clean due to the cadmium. Note those manual adjusters, too! I use'em (cause you have to.)

Removing backing plate bolts. This view gives you a good idea of the suspension geometry. More on these pieces later.

My Dad always told me to hang these things up. The rubber is brand new, by the way. Just replaced those, and the shoes and cylinder. The top pivot, easily seen here, is just a bolt. The upper control arm is actually two separate pieces. In this view, it's easier to see why how the brakes are different from the ones you're used to, and why the brakes only work in one direction.

The kingpin does not turn. It is locked in place (so it won't wiggle) by a wedge called a cotter pin in the shop manual. This wedge is pulled into place by a nut which I am removing here.

Before I can drive out the king pin, I need to remove the wedge, and also I need to remove a cap on the top of the king pin. This cap just keeps the dirt out and grease in. You just have to destroy it (as I am here) or you can drill and tap it, and pull it with a bolt.

After sufficient mangling with a cold chisel, it has buckled enough to raise a lip on one side.

And there's the top of the pin.

It's not easy to drive the wedge out, and I didn't want to destroy the threads, so I used the cap to hammer on. It's soft.

So here's the wedge. It's like a shouldered bolt with an angle cut on one side. The way this is made, you can see that is might not come out in a very friendly way.

So it turns out, the steering arm is in the way of the king pin's bottom end, so it has to come off.

To keep the front bolt head clear of the suspension, a little extra convincing is required.

There is a bottom grease cap too, but we'll just blow it off when we hammer out the king pin. You need a random suitable object to hammer on. You need fire. You need 3 pound mini sledge hammer. You might need patience.

You know you're on your way when the dust cap blows out.

And here she is. Looks like I didn't lubricate that enough. My own fault.

The spindle can now be removed, and you can see there are some take-up shims in there. There is a ball thrust bearing on the bottom that the weight of the truck sits on.

When this truck was assembled, in August of 1969, they sucked a shim down the throat of the thrust washer. Just a curiosity.

Using the ol' 3 pound hammer, and a suitably sized object, the brass shims can now be removed.



They're split, which I did not expect. These things have to be reamed to size on the truck, so there's nothing really dimensionally accurate about them.

So, back on the suspension, I removed the top pivot bushings for replacement.



Got our money's worth out of that one, didn't we? Luckily, you can still get new ones.

The lower pivots provide most (or all) of the rigidity for braking, and they are mechanically exact. They don't contain any rubber connection. I decided that the lower pivots were still in good condition and don't need replacement, but I did clean out the old grease. These things are really interesting. There is a threaded bolt captured in the bottom of the steering knuckle. The lower control arm is connected to it with a couple of nuts. When the suspension moves, these nuts screw and unscrew themselves on this bolt. Forever. If you've ever wondered how many times you could turn a bolt before the threads wear out, here's the application of that idea.

This nut has threads on the inside and outside. The inside threads move all the time. The outside threads affix it to the lower control arm, and they don't slip. Since the threads aren't related, it's possible to get in the wrong "place." It should also be evident that the spindle is threading itself fore and aft when the suspension goes up and down.