KINGPINS


Q:

I have a recurring problem on my 1960 Corvette, and I hope you can shed some light on it. I have had new king pins installed twice in the last two years, and my mechanic is now telling me that the car needs them replaced once again. He even showed me the play in my front end, especially on the right side. The left appears to be fairly tight, but the pins come in pairs, so he wants to replace both sides again.


I have noticed that the car doesn’t steer as well as it did, and I have had two front wheel alignments done, and parts replaced several times. Each time, the car seems to steer and handle better, but only for a short time. Soon, it starts doing the same thing again.

My wheel bearings, shocks, “A” arm bushings and third arm bearing have all been replaced, along with two sets of kingpins. What is causing the king pins to wear out so fast?


A:

I read your question with great interest because I have heard it all before. I may be able to help.


You are right! You are not wearing out your new king pins that fast.


The king pins are important in holding the front wheels rigid while still allowing them to turn in both directions. When you support the car on a lift, with the wheels hanging loose, you can check the tightness of the king pins by grasping the front wheel with one hand at 12:00 and one at 6:00, and wiggle the wheel up and down. (Pull out at the top while pushing in at the bottom, and visa-versa) The wheel should be firmly attached. It should not have “play” in and out.


Please be aware that you must have the wheel bearings properly adjusted, or you may be confused by looseness there. If there is any play, you should look around on the backside of the wheel while someone else is moving it, and see where the looseness is located.

What are the parts called, and how do you identify them?


The parts we are looking for are called the knuckle and the spindle. The knuckle is the heavy, forged vertical structure, right behind the brake backing plate that attaches to the outboard end of the upper control arm at its top, and to the outboard end of the lower control arm at its bottom. (You called the control arms “A” arms in your letter) The knuckle supports the spindle, and, therefore also the wheel and tire, and it moves up and down with the movement of the control arm as the car goes over bumps in the road.


The spindle is the part that attaches to the knuckle, about half way between the upper control arm and the lower, and provides support for the wheel and tire by means of the front wheel bearings and hub. It allows the wheel to swing right and left. The spindle is mostly not visible when the car is together. You can only see the inboard part of the spindle where it attaches to the knuckle, where the grease fittings are located. Remember, the king pin fits into both the knuckle and the spindle.


Here’s the trick: If you see play between the spindle and the knuckle, you might jump to the conclusion that the king pin is worn. This may not be true. Please remember that the king pin needs to be properly fitted in both the knuckle and in the spindle. Looseness in either place will appear to be wear in the king pin. If it has looseness in either of these two places, the wheel will rock in and out. The problem is that the king pin may be in perfect condition, and simply not locked rigidly in the knuckle. The king pin, when installed, must be locked in a perfectly rigid manner in the knuckle. This is done by the fact that it is a precision fit to the knuckle, fitting tightly into a machined bore; and it is locked by means of a wedge bolt that is designed to pull tightly into the knuckle when you tighten the nut on its threaded end. This wedge bolt will lock the king pin to the knuckle with no possible chance of movement, as long as everything is good.


I have seen this mistake many times. I have to admit that it is easy to be fooled by this one. You really have to look closely in order to see just where the play originates. It looks almost exactly the same if the king pin is worn, or if it is just loose in the knuckle.


Here is the problem; if the knuckle is worn, causing this looseness, it isn’t just a simple job of tightening the wedge bolt. It is an indication that the knuckle is damaged where it mates with the pin. That precision bore I mentioned earlier, the one that is supposed to just exactly fit the size of the king pin, is probably worn out from perfectly round to oval. If that is the case, the knuckle should be replaced with a good one. It could possibly be repaired by a good machine shop, but I believe that it would cost more money, and have less longevity than finding a good, used knuckle and exchanging it for the defective one.


Check out this situation on your Corvette. King pins don’t wear out nearly as fast as you have been experiencing. This just may be the problem.