47-55.1 Steering geometry question

[TX3100Guy]

While I'm waiting on my engine re-re-build, I began chasing other minor issues that I've noticed. One of the issues involved the steering stabilizer that I installed a while back. In the few short rides I took in the truck prior to realizing that the engine needed re-built, I thought I noticed that the truck could turn a tighter turn in one direction than the other. At the time, I made a mental note to check the stabilizer to ensure I hadn't installed it in such a way as to prevent a full lock to lock turn.

Today, I jacked up the front axle and first did a full turn of the steering wheel to the left. At that point, I noticed that the drivers side wheel appeared to be turned further to the left than the passenger side. Then I turned the steeling wheel to the right fully and noticed that the passenger side wheel appeared to be turn further to the right than the drivers side wheel.

Am I imagining things? Is this normal behavior? If this isn't normal behavior, what could/would cause it?

[geezer#99]

Sounds normal.
It’s called Ackerman.
Here’s a wiki on it.


https://en.wikipedia.org/wiki/Ackerm...ferent%20radii.

[TX3100Guy]

Originally Posted by geezer#99

Sounds normal.
It’s called Ackerman.
Here’s a wiki on it.


https://en.wikipedia.org/wiki/Ackerm...ferent%20radii.

Thank you. I learn something new everyday!

[mr48chev]

Originally Posted by geezer#99

Sounds normal.
It’s called Ackerman.
Here’s a wiki on it.


https://en.wikipedia.org/wiki/Ackerm...ferent%20radii.

It's not Ackerman even though the Ackerman principal applies to some respect.

Ackerman is far more about the rear axle tracking in a smooth line behind the front axle on a turn.

Internet wise the workd 'ACKERMAN" brought up by someone answering a question on chassis is quite akin to the third grader who always wants to be first to raise his hand in class to make the other kids think he actually knows something but can't give the real answer.

Back to TX3100 guys question, Stock AD trucks don't turn as tight a radius circle in one direction as they do in the other. The stabalizer may be running out of travel in one direction or the other and you can adjust that but I am pretty sure that if you take it loose and do the empty parking lot turn it to lock and mark the circle or 90 degree turn in each direction the circle will be different side to side.

From the factory alignment specs you have to scroll way way down the page to the steering box section to find the turning radius chart. A and be are tires on the ground turning circle for A and turning circle clearance for B.

As far as Ackerman principal goes as applied to our trucks that might be and issue when we stick an MII front end under a long bed chassis where the A arms of the MII set up to have correct Ackerman with a 96.2 inch wheel base are dealing with a 125-1/4 inch wheel base. Then the back tires might not want to track smoothly around a turn. Car hobby wise that is where Ackerman is an issue, when you are swapping steering pieces between radically different wheelbases. You would know if it is off if you were in a large empty parking lot and had a puddle to drive through to get the tires wet and drove through the puddle and got out and checked how the rear tires followed the front tires in the circle. did their turn circle smoothly match the turn circle of the front tires or is it a bit off from the circle of the front tires. If Ackerman is on point you will have four matching (not touching) tracks that are even The further off it is the more the rear tracks won't match the front tracks as far as being even.

[leegreen]

Originally Posted by mr48chev

Stock AD trucks don't turn as tight a radius circle in one direction as they do in the other.

Why is that?
I could not find a turning radius chart in the manual I looked at, but they did give a toe out spec for full lock, but only one, not a different one for right and left sides.

I have never driven a stock AD except in a field, but my experience has been that anything with a noticeably different turning radius in one direction has something wrong with it; bent, worn out, badly adjusted.

ps: the 3rd grade comment was harsh and undeserved

[TX3100Guy]

Originally Posted by leegreen

Why is that?
I could not find a turning radius chart in the manual I looked at, but they did give a toe out spec for full lock, but only one, not a different one for right and left sides.

I have never driven a stock AD except in a field, but my experience has been that anything with a noticeably different turning radius in one direction has something wrong with it; bent, worn out, badly adjusted.

ps: the 3rd grade comment was harsh and undeserved

All my steering components show no signs of damage or excessive wear. Despite the earlier comment, my wheels look exactly like the illustration on the Ackerman illustration on Wikipedia.

ps. I agree the 3rd grade comment was unnecessary and in poor taste.

[mr48chev]

Originally Posted by leegreen

Why is that?
I could not find a turning radius chart in the manual I looked at, but they did give a toe out spec for full lock, but only one, not a different one for right and left sides.

I have never driven a stock AD except in a field, but my experience has been that anything with a noticeably different turning radius in one direction has something wrong with it; bent, worn out, badly adjusted.

ps: the 3rd grade comment was harsh and undeserved

It's not a huge difference and it may not be on all models. A quick check is to have the truck up on blocks and turn the wheel to lock one way with the steering wheel and see if the spindle hits the stop on the axle and turn it all the way the other way and see if hits the stop on that side.

I'm thinking that you could probably go out and get in most any vehicle you own and take it out and drive a circle to the left and drive a circle to the right and they won't be the exact same diameter though. Close and within 18 inches and maybe within six but still not perfectly the same.


The call out on the throwing out the Ackerman thing was just what it is. Be it on the HAMB or FB or where ever any time steering issues come up some guy who wants others to think he knows something throws out "Ackerman". You can go on the Hamb and search out steering issues and it will always pop up.

Ackerman does affect going around a turn but what it affects is how the rear wheels follow the front wheels. It's critical on a race car but not as noticeable on street rigs. When you hang a MII front end under a 3100 you are dealing with 20 inches difference in wheel base but for the most part they drive pretty good if they are set up right. The issue comes when you are turning and the rear wheels don't quite follow the front wheels the way you expect. Get over in Dsraven's world and some outfit wants a semi frame stretches several feet to do what they want to do with the truck and it really shows up. You have to go at a tight turn a whole bunch different than you did before.

[dsraven]

-jack the front wheels off the ground and place stands under the axle so the weight of the truck is still on the springs
-do a steering lock to lock check and count the number of turns, exactly. I like to turn the wheels to one lock and put some masking tape on the steering wheel at the top, then turn to the other lock, counting as you go, then see where you end up for turns and partial turns
-next divide the number of turns by 2 and back the steering wheel off, from one lock, that number of turns. this centers the steering box, which is important because the gears in the box are cut to have a high spot at the center so when driving down a straight road the steering feels nice and tight but is looser on turns so the steering will easily self center when done the turn. this works in conjuction with king pin inclination to always want to be centered with the weight of the vehicle on the wheels
-next put a rubber strap or rope or whatever on the steering wheel to lock it in place at center or have a helper hold the wheel from moving.
-now go outside the truck and see if the wheels are pointing straight ahead. sometimes you can measure from the inside of the tire sidewall to the frame on each side, left and right, and compare the dimensions.
-there are also usually steering stop adjustment bolts or plates to adjust the max turn the steering can make before bottoming on these bolts. they are bolted on with the kingpin retainer wedge bolt I think. been awhile since I was working on a solid axle.
-if you find the wheels are way outta whack there are adjustable drag links available possibly. I have seen them for the task force trucks anyway. they get used for trucks that keep the solid axle but are lower than stock
here is a link I found that shows the steering stop brackets. one of the pics shows the kingping retainer wedge bolt attached.
https://67-72chevytrucks.com/vboard/...d.php?t=794877

[dsraven]

when working on semi trucks and trailers I would use a plumb bob and mark the center of each axle on the floor under the unit. then do some dimension checks to see if the axles were tracking correctly and do adjustments required. this ensured the trucks and trailers tracked straight down the road. some were out of whack enough so you would notice the "dogtracking" trailer if you were driving behind it or sometimes the operators would tell us they could see all the way down one side of the trailer but not the other side.

[dsraven]

"dogtracking" also makes it turn further one way than the other because it's already sorta turned one way just to keep going straight in the lane

[Rickysnickers]

Ok, let's get back to the subject at hand and discuss helping the OP.

[dsraven]

center the steering box, lock to lock, then see where the wheels are pointing. if they are straight ahead then check the steering stops. start simple, go from there. since the engine is out the steering should turn pretty easy but jacking it up would take the strain off parts.

[TX3100Guy]

Originally Posted by dsraven

center the steering box, lock to lock, then see where the wheels are pointing. if they are straight ahead then check the steering stops. start simple, go from there. since the engine is out the steering should turn pretty easy but jacking it up would take the strain off parts.

Busy with "honey do" items tomorrow, but I'll do it again and post pictures of the wheels on both sides at full lock each way.

[mr48chev]

When answering a question on the HAMB a thought just came up. Check and see if your truck has the steering stop tabs under the king pin pinch bolt nut on both sides. It's just a piece of flat bar with a hold drilled in it and the end is bent at an angle for the spindle to contact it as a steering stop. If one of those is missing the truck will turn a lot tighter in that direction as in too tight than it does in the other direction. I'll get a photo tomorrow if it isn't so wet and nasty that it isn't doable. they are missing off my axle but are on the axle going under my speedster roadster.

[1project2many]

All my steering components show no signs of damage or excessive wear. Despite the earlier comment, my wheels look exactly like the illustration on the Ackerman illustration on Wikipedia.

The Ackermann patent (for a front axle and steering linkage design by German carriage builder named Lankensperger) illustrated the principal of steering the wheels to different angles to reduce scrubbing. The illustrated design in the patent didn't work well.

In the OEM AD truck manual, the illustration commonly used for Ackermann Angle is in a section titled "Steering Geometry." It's also referred to as "error," "Steering Angularity," and "Toe out on turns." As this was published right after WWII I wonder if GM just didn't want the earlier German design associated with their vehicles.

Today, I jacked up the front axle and first did a full turn of the steering wheel to the left. At that point, I noticed that the drivers side wheel appeared to be turned further to the left than the passenger side. Then I turned the steeling wheel to the right fully and noticed that the passenger side wheel appeared to be turn further to the right than the drivers side wheel.

This is exactly how it should be, although there are many compromises built into our trucks. For example, the difference in angle of the wheels during a turn depends on the distance between front and rear axle centerlines. But short and long wheelbase trucks use the same steering knuckles and axles. There are simulation tools that will allow you to enter data for your steering and suspension system to simulate changes and check optimization, but other than replacing a damaged stock part there are no easy adjustments if you want to make improvements.

Busy with "honey do" items tomorrow, but I'll do it again and post pictures of the wheels on both sides at full lock each way.

If the knuckles are hitting the stops on both sides then the truck should turn through the same radius for LH and RH turns. A significantly different turning radius could be caused by damaged steering knuckles or an axle centerline that is not perpendicular to the truck centerline.

I could not find a turning radius chart in the manual I looked at, but they did give a toe out spec for full lock, but only one, not a different one for right and left sides.

This definitely suggests that the minimum turning radius is expected to be the same for LH and RH turns. I can't really think of a reason why the truck would be built to have a different turning radius L<->R. But I'm willing to learn.

[TX3100Guy]

After jacking the front axle up and turning the steering wheel to the left and the right, I noticed several things.

1) the steering wheel turned the exact same number of rotations left and right (about 1 3/4 turn give or take a smidge)

2) I noticed the bracket that is causing the steering knuckle to stop. The bracket and its bolt are hitting one of the bolts holding the brake caliper bracket.

3) when I removed the bracket from both sides, then the bolt/stud that held the bracket is hitting the nut on the brake caliper bracket, but the steering wheel turns just a shade further in each direction.

Here is a view from the front of the truck with the wheels turned fully in each direction.






Now that I've removed the bracket but left the bolt/stud in with its nut, the question is, does this bolt/stud with its nut server any other purpose relative to the king pin? Can I remove it fully by tapping it out?

[mr48chev]

That "bracket" is the factory steering stop that I was going to go out and take photos of yesterday and didn't manage to.

The not turning all that tight is because the disk brake piece get in the way of fully turning what would if it had drum brake backing plates on it.

You could trim the end of the king pin pinch bolt a bit to let it turn further but you don't want it to turn tighter than a stock truck with drum brakes does. My 48 doesn't have those stops on it and yup I can do a tighter turn either way but it can actually go to far and hang up a bit. My buddy had put new king pins in the axle before he gave me frame and axle after he sold the cab and sheet metal to someone else. Either he or someone before him left the stops off.

[mr48chev]

I lightened up the photo to see the details a bit better and would say on yours leaving the factory stops off is doing the right thing as the caliper brackets are taking up that turning space you normally would have. We will have to put that in the reference file because the question no doubt will get asked again.

I'm not sure if it is viable to knock the pinch bolts out and put them in from the back to get a bit more turning space. Cutting a bit off the end of the pinch bolt that sticks out of the nut won't hurt because new ones normally come with every kingpin set. That might be a trial and error thing. If you are happy with how tight it turns without the stops so be it if you want it to turn a bit tighter you now are on the way to figuring out how to get it to where you want it.

[TX3100Guy]

Originally Posted by mr48chev

I lightened up the photo to see the details a bit better and would say on yours leaving the factory stops off is doing the right thing as the caliper brackets are taking up that turning space you normally would have. We will have to put that in the reference file because the question no doubt will get asked again.

I'm not sure if it is viable to knock the pinch bolts out and put them in from the back to get a bit more turning space. Cutting a bit off the end of the pinch bolt that sticks out of the nut won't hurt because new ones normally come with every kingpin set. That might be a trial and error thing. If you are happy with how tight it turns without the stops so be it if you want it to turn a bit tighter you now are on the way to figuring out how to get it to where you want it.

Thank you.

[dsraven]

The bolt that goes through the solid axle and edge of kingpin is a required bolt. It is actually a wedges shaped bolt that retains the kingpin. Don't take it out. The ends of all the hardware could be shaved off back to the head of the nut if you wanted and that would gain some more clearance. A narrower nut could be used as well but ensure it's grade 8 in that case.

[TX3100Guy]

I'll leave the bolt in but leave the bracket off. I may just leave the bolt the length it is, in case I have to reverse this down the road.

[dsraven]

I suggest to try it that way, keep the brackets. If you find it turns so hard the kingpin inclination can't bring it back then maybe install the brackets again and, after making a dimension check and writing it down, you could shorten the brackets to your liking.
I would actually grind the ends of the bracket bolts off first. They look longer than stock. Maybe that's the problem. Could they be installed backwards so it's just the bolt heads you would see sticking out?

[mr48chev]

I went out and looked at the one I have and the stop on it would never work with a disk brake caliper. That is probably a late 30's axle that came with Bendix brakes that I swapped to a member for Huck brakes so I can run 18 inch 30 something Chevy wires on that axle. Some day the rig that goes on will be on the trailer behind one of my forum friendly trucks.

[mr48chev]

Just looking at those photos of your spindle/axle/steering stop the number of threads sticking out past the nut on the pinch bolt are what is considered to be perfect. as long as you have close to 3 threads sticking out past the nut on that bolt you can cut off what ever keeps it from turning far enough without a worry. I'd be doing a test drive and decide that "Yea, that is what I want" or " I still need it to turn a tad tighter" and go from there.