Why couldn't shops figure out these problems?


I have to repack the front wheel bearings on my truck once in a while. Even with the 4wd making the job a little more complicated, compared with what’s required to replace front wheel bearings on my Corolla, the truck’s repacking job is easy peasy.


I seem to have been very lucky @db4690. I have never replaced a worn out ball joint, king pin or tie rod end(excluding innners on rack and pinions) on a vehicle that I serviced regularly. And dozens of vehicles ran 300,000 miles.


I’ve had to replace a pretty fair number of steering and suspension components; even on some of my cars which received regular grease jobs.

The road surfaces here will trash anything no matter how well it’s built or how regularly it’s maintained. It’s not looking any better either. Last week they started piling up gravel and brought in road machines.
That means resurfacing and every time they do the road ends up worse than it was before.


Maybe I should have mentioned that I have replaced ball joints, etc., that were damaged from striking pot holes, etc. And I have even replaced ripped boots on suspension components that were left in place into infinity… Or possibly the day after I closed up shop. Who knows.


Just curious, are king pins, ball joints, and struts mutually exclusive?; i.e. for any given vehicle, just one of those designs is used for the front suspension ?


Not really.
The “king pin” is a steering part that controls the angles of the steering rotation.
While the correct term for a strut-based system is “steering angle inclination (SAI)”, “king pin” inclination is still commonly used. Note that this angle includes both camber and caster.

A “strut” is a different discussion. A strut combines the spring and the shock absorber, but in a way different from a “coil over”. A strut is a part of the system that controls the movement of the steering knuckle throughout its range as well as just absorbing shocks. Struts won’t have ball joint on the bottom, because they’ll be bolted directly to the steering knuckle, but there’ll be control arms on the bottom that locate the bottom of the steering knuckle, and those’ll have joints on it that may be ball joints.

There are a number of different ways suspensions are designed. The June 2017 issue of Car & Driver has a decent primer on suspension systems that shows a few of them. It’s worth the price.

See the attached diagrams.


With double ‘A’ arm, you get two ball joints.
With strut, you get one ball joint.
With king pin, you get no ball joint.



With McPherson suspension the strut replaces the upper ball joint with a strut bushing at the upper mount and a lower ball joint mounted at the bottom. King pin style suspensions on light trucks these days use ball joints and 4 wheel drives used tapered bearings for years but currently use ball joints but the geometry is often anachronistically referred to as king pin. Independent front suspension first used king pins with wrist pins until ball joints were developed.

@TSM’s diagrams show the King pin inclination which remains the term for describing the relationship between the center of rotation when steering and the camber angle of the wheel regardless whether a king pin or ball joints are used.


It should be noted that the ball joint with struts will not be on the struts themselves but on the steering knuckles.

It should also be understood that the diagrams I posted only show camber angles. SAI, or “kingpin angle”, is actually a combination of camber and caster… of the steering knuckle turning axis, NOT of the wheel. Yeah, I know, that doesn’t sound right to me either. But I’m tryin’ to articulate a complicated thing.

One thing I’ve learned from this thread is that it’s difficult to explain these things without a whiteboard and a marker. It seems simple when one understands it, but it really isn’t. :stuck_out_tongue_winking_eye:



[quote=“the_same_mountainbik, post:9, topic:105851”]
“asses in the classes”
[/quote] :joy::disappointed_relieved:

Yup and colleges just love those. No expensive profs required just a starving grad student and the checks come in… And when they do get in an actual college class it will be an easy freshman class also taught by a grad student . When they eventually do flunk out, no worry plenty more where they came from and they can still have a reasonably educated graduating class to maintain their reputation.

Here in New York we now have free state colleges a good thing but I hope we can maintain some minimum quality level.


I have to disagree here…and agree with MtnBike.

I’m going to relate this to computer science. There is zero work related to learn Assembly Language programming. However all the top schools that have computer science degrees require an Assembly Language course. It gives the student a good basic understanding of how computer works and makes them think a different way.

Learning about carburetors gives a student a basic understand of how air/fuel is metered. May not be every day practical application, but it is good for theory.


But those computer science degrees are not requiring that you pass the Assembly class by programming on an actual EDSAC.

You can learn about air/fuel mixing and metering without having to work on a carburetor.


True…but why would you. When I programmed in Assembly it was with a computer developed in that decade. Today - Assembly Language is only used by people who write device drivers and operating systems…And still most of that type programming is done in C.


That’s my point. Fuel and air is still being metered today, it’s just being done with fuel injection. Nothing says you can’t learn the metering concepts while still keeping things modern. You learned what you needed to learn by sitting in front of a modern computer typing on a modern keyboard. You didn’t need the EDSAC’s punch-tape input.

I mean, we don’t require them to work on stage coaches in order to learn about suspensions. :wink:


You obviously understand what a few of us are talking about. Shouldn’t every academic and vocational entry level course start with the basics. I recall my high school auto mechanic course at first seemed so basic it was insulting. I soon realized the instructor had to expect one or two students who did not know how to check engine oil level. In phase one we learned to identify components, what they did, and how they did it. Followed by why they did it and how they worked together. It certainly helped the flow charts in phase two ‘diagnostics’ make sense. The finest neurosurgeons started in pre-med.


Yep. As long as there’s an option to test out for people who already know that stuff. Back when I went to college many people still didn’t own a home computer, and I was highly annoyed at the required “computers and technology in society” course that you could not test out of, and which was going over basics like “This is a mouse. This is how you select things with the mouse. Here’s the difference between a click and a drag,” etc.

Total waste of time for those of us who were nerds in high school and ran our own bulletin board systems before the internet was available outside of the government and colleges, but several of my classmates had never messed with a computer in their lives so the class was definitely necessary.

I can see the guy who’s been working on cars since he was handing tools to his dad after getting home from kindergarten might be a little irritated at having to sit in a class and twiddle his thumbs while other people learned about lug nuts and dipsticks, but it should certainly be taught to those who need it.


You can, but a Fuel injection system is a lot more complicated. The theory is easier to understand from a simpler system…one that you can easily change and play with.


This was school year 1968/1969. There was no “test out” option. I didn’t have much hands on auto maintenance/repair experience. I had been helping my Father check oil and coolant levels since the age of 5. Two students were working at service stations after school and weekends. I worked at a grocery store. The instructor immediately made the 2 experienced students his assistants. They helped anyone who was struggling.


You might say you are trying to articulate the articulation:wink:

Thanks to all who provided a brief tutorial on the front suspension parts. So the struts, kingpins, and ball-joints are mutually exclusive for the most part, except that struts also have a lower ball-joint at the steering knuckle. I also understand that the common nomenclature sometimes uses “kingpin” where no kingpin actually exists.

One point of add’l clarity, does the lower ball-joint on a strut front suspension connect the lower part of the strut to the steering knuckle ?


Nope. The strut bolts directly to the steering knuckle. The ball joint then connects the bottom of the steering knuckle to the lower control arm. The steering then pivots around the ball joint and the strut together.

In the attached drawing, the bottom of the strut’s main body (shank, if you will, item 4) shows what looks like a clamp at the end with two bot holes. Those two holes bolt to the two holes in the knuckle (item 3). Item 11, the ball joint assembly, mounts to item 10, the lower control arm. The control arm rotates on the transverse support/ engine mount, and the action is transferred through the ball joint and the steering knuckle up into the strut.