How to adjust caster (if indeed you can with stock parts?)

[MoPar~Man]

Kingpin inclination.
The top ball joint is closer to the car than the lower ball joint. This is called the kingpin angle. This makes the spindle bearing shaft drop when the tires are turned left or right, and rise when the tires are running straight. That makes the car rise when the wheel is turned and drop when the wheel is straight. That makes the car run in a straight line and return to center coming out of parking lots.

The top ball joint is closer to the (center?) of the car than the lower ball joint. That's kingpin angle? Is that not camber?

This is cracked. On our cars the spindle is always 90 degrees to the knuckle. So when will kingpin inclination ever not be camber angle?

 

[Just Carbs]

I thought it was settled that shops today have no clue how to work with our cars, and if they did they'd be using specs that were correct for bias tires and not radials?

Is this not true?

Well, maybe they are only seeing new strut cars? I don't fault them for not being handy with our old cars. A good truck shop could probably do it.
And as said earlier, it depends on the radial tire.

 

[Just Carbs]

The top ball joint is closer to the (center?) of the car than the lower ball joint. That's kingpin angle? Is that not camber?

The spindle shaft is not cast 90 degrees to the ball joints. Thats called included kingpin angle. It can't be adjusted.
Setting the camber is accomplished by moving the ball joint in and out from the motor. It doesn't affect factory cast in kingpin inclination/angle.
Get this book. It's all in there.

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[MoPar~Man]

This simple question is still out there.

If my height is correct, if my toe is zero,

Should my wheels self-center if I max out the caster?

Do your C-body wheels self center, like your (you name it) front-wheel-drive sedan with macpherson struts?

 

[Just Carbs]

Yes. It will when coming out of a turn in town and driving through slow and moderate speed turns.
But on straight roads it will follow the road crown or wind force.
Caster will make the car follow any force presented to it. It's only ability to run straight is from the forward inertia of the car.
The factory kingpin inclination is there to make the car self-center in all conditions and reduce the amount of effort needed to drive the car on the interstate. The minimum caster driving experience is directly opposite to the newer popular Firm Feel experience that requires more steering wheel effort to drive the car.

 

[Just Carbs]

This simple question is still out there.

If my height is correct, if my toe is zero,

Should my wheels self-center if I max out the caster?

Do your C-body wheels self center, like your (you name it) front-wheel-drive sedan with macpherson struts?

Yes, my 64c, 72c and 75 Dart and 87 Fifth Ave do self-center.
I didn't explore the setup on the 98 Deville that I just sold because it required a very high steering effort on the interstate that I suspect was due in part to the firm feel style rack and pinion steering setup.

 

[MoPar~Man]

In 2007 Hunter Engineering (they make alignment systems) put out a white paper discussing the math behind measuring caster from camber angles:

https://rennlist.com/forums/attachments/928-forum/1317404d1602722988-home-diy-alignment-master-thread-hunter-caster-white-paper.pdf

I used their equations 7 and 8 to measure what my caster is (on my driver's side wheel anyways). I put the front wheels on pair of greased plates and I put the parking brake on to prevent the front wheels from sliding around during all this. This gave great position reproducibility when I turned the front wheels back and forth (easily able to do this without the engine running).

I clamped a pair of long aluminum bar clamps to the wheel so I could get an angle (toe) measurement and so I could set the 2 positions to take camber measurement on. The various hand-held camber / castor levels want you to turn the wheel to 2 positions 20 degrees off center and take camber measurements at each one (or zero a scale at one position and read the caster at the other position).

I bought one of those small magnetic camber-only guage and a digital construction level. I took the center cap off the magnum rim (and took the dust cover off the spindle) but I didn't come up with a way to accurately place the camber guage on the rim, but I took some measurements with it anyways. The digital level was exactly the right length to make contact with the edges of the rim (and clear the spindle). The level produced very reproducible results on a variety of structures I tried it on (various metal door frames and other vertical surfaces).

I found that the front wheel could be turned through about 60 degrees from lock-to-lock, but it wasn't symetrical, so I settled on 29 degrees left, 29 degrees right (58 total degrees).

The upper control arm was set such that it was pulled in towards the center of the car by both adjusting bolts. This should theoretically give maximum negative camber.

The digital level said I had -2 degrees of camber at the left-turn and center wheel positions and zero camber at the right-turn position. The camber guage said -3 degrees for left and center and zero for the right position.

Plugging these numbers into the caster equation resulted in a positive 1.89 degrees of caster.

The service manual specs actually call for different camber numbers between the front wheels: 1/2 degree on the left, 1/4 degree on the right. For caster it calls for .25 to 1.25 degrees. But these specs are for bias tires, which are very conservative on camber (for tire wear) and caster (for steering effort). The specs sacrifice cornering traction and self-centering force.

Knowing that I'm able to exceed the FSM specs in both caster and camber is reasuring but it doesn't help me figure out why the car has an extreme tendency to turn left or right when driving straight at the slow speeds I've been using so far. The center position is an unstable equilibrium position, the exact opposite of what I want and expect.

And something else- I was under the impression that when turning the wheels to the left or right, that the front end should rise up slightly (driver's side rise up when turning left, passenger side rise up when turning right). Putting a level on the hood and observing it while an assistant turns the wheels, I note absolutely no change in height.

 

[Just Carbs]

In 2007 Hunter Engineering (they make alignment systems) put out a white paper discussing the math behind measuring caster from camber angles:

https://rennlist.com/forums/attachments/928-forum/1317404d1602722988-home-diy-alignment-master-thread-hunter-caster-white-paper.pdf

I used their equations 7 and 8 to measure what my caster is (on my driver's side wheel anyways). I put the front wheels on pair of greased plates and I put the parking brake on to prevent the front wheels from sliding around during all this. This gave great position reproducibility when I turned the front wheels back and forth (easily able to do this without the engine running).

I clamped a pair of long aluminum bar clamps to the wheel so I could get an angle (toe) measurement and so I could set the 2 positions to take camber measurement on. The various hand-held camber / castor levels want you to turn the wheel to 2 positions 20 degrees off center and take camber measurements at each one (or zero a scale at one position and read the caster at the other position).

View attachment 688967

I bought one of those small magnetic camber-only guage and a digital construction level. I took the center cap off the magnum rim (and took the dust cover off the spindle) but I didn't come up with a way to accurately place the camber guage on the rim, but I took some measurements with it anyways. The digital level was exactly the right length to make contact with the edges of the rim (and clear the spindle). The level produced very reproducible results on a variety of structures I tried it on (various metal door frames and other vertical surfaces).

View attachment 688970

I found that the front wheel could be turned through about 60 degrees from lock-to-lock, but it wasn't symetrical, so I settled on 29 degrees left, 29 degrees right (58 total degrees).

The upper control arm was set such that it was pulled in towards the center of the car by both adjusting bolts. This should theoretically give maximum negative camber.

The digital level said I had -2 degrees of camber at the left-turn and center wheel positions and zero camber at the right-turn position. The camber guage said -3 degrees for left and center and zero for the right position.

Plugging these numbers into the caster equation resulted in a positive 1.89 degrees of caster.

The service manual specs actually call for different camber numbers between the front wheels: 1/2 degree on the left, 1/4 degree on the right. For caster it calls for .25 to 1.25 degrees. But these specs are for bias tires, which are very conservative on camber (for tire wear) and caster (for steering effort). The specs sacrifice cornering traction and self-centering force.

Knowing that I'm able to exceed the FSM specs in both caster and camber is reasuring but it doesn't help me figure out why the car has an extreme tendency to turn left or right when driving straight at the slow speeds I've been using so far. The center position is an unstable equilibrium position, the exact opposite of what I want and expect.

And something else- I was under the impression that when turning the wheels to the left or right, that the front end should rise up slightly (driver's side rise up when turning left, passenger side rise up when turning right). Putting a level on the hood and observing it while an assistant turns the wheels, I note absolutely no change in height.

Did you get the $100 magnet gauge that clamps directly on to and around the spindle hub bearing? In which case you would mount the standard no magnum spare wheel/tire from the trunk on the car to use it so it will fit? I guarantee life will be sooooo much better if you can. And, it does read DIRECTLY off the spindle, something that the fancy dancey shop stuff don't do. So, unlike the shops clamp on the wheel things it's oblivious to bent wheels. Or did you get the little $10 one that sticks to the disc brake cars that you can't use on your car?

Anyway.
If not then check the camber with the wheel rotated to 4 different positions 90 degrees apart to make sure the wheel is not bent, and the extreme outer edge is consistent all the way around the wheel.

If the caster is zero the car will rise and fall evenly, both left and right when the wheels are turned.

The camber specs do sacrifice max cornering ability, but the caster specs do not affect centering in a straight line, that's a result of kingpin inclination, included kingpin angle, steering axis inclination by different names, it's all the same thing. And it also assists centering when leaving parking lots.

Negative camber reduces kingpin inclination ability to center the car under all driving conditions.

Positive caster will assist centering when leaving parking lots. But, it's at the expense of wind and road crown susceptibility. And requires more effort to drive the car. It increases steering effort in turns and lane changes. If you set it up with a lot of positive caster you will be fighting wind and crown.

My experience with these cars is they like 1/2 positive camber, 1/2 positive caster and minimum measurable toe.
Thats with 235/75-15 radials on standard factory wheels.
Fat tires, fat wheels, big offset? Need different numbers. Like 1/2 negative camber for sticking and 2 positive caster for steering wheel resistance when driving like we're not supposed to be.

 

[Knebel]

Normally with the limited adjustment you can also try to get as much castor as pissible without getting positive camber!

 

[Just Carbs]

Normally with the limited adjustment you can also try to get as much castor as pissible without getting positive camber!

Is the Plymouth in your avatar the car you are driving? If so, what is the front tire/wheel package and what alignment numbers do you like on it?

 

[MoPar~Man]

I got the cheapee $25 guage so unless I come up with a plate welded to a nut to screw on the end of the spindle, I can't get it to sit on the spindle as-is. The spindle nut seems to be the same size/thread as the lower control arm pivot-shaft nut.

> If the caster is zero the car will rise and fall evenly, both left and right when the wheels are turned.

Are you saying that if the caster is not zero, then I should see one side go up when I turn the wheel a certain way?

Today I was checking the toe and seeing how parallel the back wheels are to the front wheels. One thing I've noticed - the width of the rear axle (as measured to the ends of the wheel studs) seems to be 2 3/8 inches shorter than the width of the front wheels. Does anyone have good number specs on this? It means that laying a string against the tires won't give you parallel lines if I'm right.

I made sure that I didn't have toe-out, I've read that toe-out can be the cause of a wandering front end. I think I dialed in a little bit of toe-in and took the car for another drive, no change (no centering at all, can't trust the car to drive straight at very low speeds with no hands on the wheel). Even idling in park the self-turning to the right is still happening. With the engine running in park, with the wheels pointed straight, if I breath on the steering wheel it will start turning to the right. And I have "tapped" on the steering gear valve body already, moved it forward as far as it will go.

I think something is wrong with the gear, but I don't know what. I will hate taking the valve body off to check that pin because the oil will leak all over my new powder-coated frame.......

ARG

 

[Knebel]

Is the Plymouth in your avatar the car you are driving? If so, what is the front tire/wheel package and what alignment numbers do you like on it?

They are 17" rims (B/G Rodworks "oldschool") on 245/50(i think, might be 45) nitto 555 g2s. I like the combo a lot! I did the garage floor alignment and I believe as I recall I got somwhere about 3.5° castor and -1.5 camber. I basically aimed for the most castor possible thats equally archieveable on either side!

 

[Just Carbs]

I got the cheapee $25 guage so unless I come up with a plate welded to a nut to screw on the end of the spindle, I can't get it to sit on the spindle as-is. The spindle nut seems to be the same size/thread as the lower control arm pivot-shaft nut.

> If the caster is zero the car will rise and fall evenly, both left and right when the wheels are turned.

Are you saying that if the caster is not zero, then I should see one side go up when I turn the wheel a certain way?

Today I was checking the toe and seeing how parallel the back wheels are to the front wheels. One thing I've noticed - the width of the rear axle (as measured to the ends of the wheel studs) seems to be 2 3/8 inches shorter than the width of the front wheels. Does anyone have good number specs on this? It means that laying a string against the tires won't give you parallel lines if I'm right.

I made sure that I didn't have toe-out, I've read that toe-out can be the cause of a wandering front end. I think I dialed in a little bit of toe-in and took the car for another drive, no change (no centering at all, can't trust the car to drive straight at very low speeds with no hands on the wheel). Even idling in park the self-turning to the right is still happening. With the engine running in park, with the wheels pointed straight, if I breath on the steering wheel it will start turning to the right. And I have "tapped" on the steering gear valve body already, moved it forward as far as it will go.

I think something is wrong with the gear, but I don't know what. I will hate taking the valve body off to check that pin because the oil will leak all over my new powder-coated frame.......

ARG

I'm not optimistic about the welded plate to a nut thing. I suggest you go ahead and spend the $100 or so for the one that goes on the hub. If you have a standard steel wheel for a spare. I do remember seeing one piece spin on gauges that fit the spindle but don't have any experience with them.

With positive caster the left side will rise when the wheel is turned to the left, and the right side will fall before it begins to rise when the wheel is turned to the left. Same effect when the wheel is turned to the right, but inverse.

Hard to set toe off of rear axle at home, plenty of people will disagree with me on that. Set it only off the front tires, then adjust the sleeves equal amounts to center the steering wheel by trial and error when driving the car.
Get this fishing weight scale and chains, hook it on the outside of the wheels, stretch it to 20 pounds across the front tires, read the scale, roll the car forward 1/2 tire revolution and read it again at the back of the tires.

Toe out will make the car over responsive to minor steering correction on the interstate and present as hunting, not wandering. A tiny bit of steering wheel movement will produce a disproportionate over reaction from the car in that direction. But if you don't move the steering wheel "at all" it will not hunt. The car hunts because the dominant tire changes from side to side with each and every steering correction. The inside tire becomes dominant. Back and forth, back and forth.
Wandering is caused by loose/worn parts. You got no loose parts. Everything is brandy new.

Put the car on jack stands under the control arms, start the car. Does the wheel turn right?

 

[Just Carbs]

They are 17" rims (B/G Rodworks "oldschool") on 245/50(i think, might be 45) nitto 555 g2s. I like the combo a lot! I did the garage floor alignment and I believe as I recall I got somwhere about 3.5° castor and -1.5 camber. I basically aimed for the most castor possible thats equally archieveable on either side!

I put 205/55r16 on 15x8 plus one more inch offset over stock wheels on my 64 new Yorker. Needed 1 negative camber to combat bump steer, but did get away with only 1 positive caster. Car loves it. I loves it.

 

[MoPar~Man]

I'm not optimistic about the welded plate to a nut thing. I suggest you go ahead and spend the $100 or so for the one that goes on the hub. If you have a standard steel wheel for a spare. I do remember seeing one piece spin on gauges that fit the spindle but don't have any experience with them.

With positive caster the left side will rise when the wheel is turned to the left, and the right side will fall before it begins to rise when the wheel is turned to the left. Same effect when the wheel is turned to the right, but inverse.

Put the car on jack stands under the control arms, start the car. Does the wheel turn right?

The digital level I got (off amazon for $50 CAD) is 14.5 inches long and fits nicely against the 14" magnum rim (with center cap and spindle dust cap removed) without tire interference. I agree that jacking the wheel and rotating it to verify the level reads the same value all around is a good check. The level has precision and accuracy when tested on stationary surfaces. The level reads camber directly when used in this manner, and can directly replace the smaller dedicated camber guages. There is a longer version of this level, which would be needed for those with 15 " or larger rims, but some offset hardware would need to be affixed to the level to allow contact with the wheel and clear the tire. Or use the shorter level with an appropriate length straight edge, angle-iron etc.

Again I note that I appear to have -2 degrees of camber on the driver's wheel when centered or turned to the left and 0 camber when turned right. Resulting caster calculation gives positive 1.8 or 1.9 degrees caster. No height change is noted when the wheels are turned lock to lock, but I will measure this more directly (ground to fender landmark directly) at some point.

In park with the engine running and the wheels on the ground, the wheels will self-steer (slowly) to the left from a centered position or a position slightly to the right of center, they are less likely to do this from a left of center position I think. Interesting that when I search for this self-steering phenomena (u-tube and other car forums) I believe I've only seen mention of right-turn self steering.

I should probably put this diagram in one of the other threads I've started here regarding steering - but I did change a couple of seals on the steering-input shaft side of the steering gear. When doing so I removed the cluster of parts on the right-side of this photo (housing head, spring washer and reaction ring):

Those parts just fall out when you take off the large external ring (or "castle") nut. I either incorrectly placed the washer or ring back in when reassembling it, or I over or under-tightened the ring nut. At least it doesn't leak from there any more. During this service, I did not touch the valve body. The car's steering was working fine before I did this. I moved the steering gear (with pitman arm, center link and idler arm still attached) from the old stub to the new stub.

The PS fluid prior to doing all this was 100% ATF+4 (red). After moving the gear to the new stub I naturally lost some fluid, I topped up the system with some sort of generic (clear) PS fluid. So the system now has a combination of fluids. Not sure if this is a factor in steering gear operation.

When I park the car for winter storage I'll remove the steering gear (probably with center link still attached) and have another look at it, take that ring nut off and pull those parts out, see if I put them in correctly or not.