Caster Correction Options, Differences, and Opinions

[Ebag333]

This is dumb. You guys can argue all day. Your truck will need "X' caster correction at "X" lift. But what about guys like me with 5-6" of lift.? I have no option to compare. I have to go with new arms.

You could weld the mounts for the control arms on top of the axle.

 

[landtank]

I'm not arguing with anyone, just posting up some info to help people understand the differences between how I alter caster compared to similar solutions. This is the point of this thread isn't it?

 

[bpassmore]

Yes, and I appreciate it.

I want to keep this as an information repository. With the thread title written like this, it should be even easier to find when people search.

I have learned more about both Slees and Rick's plates, and this helps me make a decision on which to choose.

Rick's has an added advantage on how the spring mounts are angled, correct? How is it different from other caster correction implementations? Why would Rick's system keep the spring perches more level than any other axle rotation system? Is it because the rear control arm axle mounting point is lowered, and not just used as a pivot point?

And one last thing (to Rick and Christo) - thank you for posting your insight and solutions for us. I truly appreciate it.

 

[sleeoffroad]

Rick, are those drawings to scale or just to illustrate the point. Also are the black circles supposed to represent the tires/axle tube with the center being the center of the axle tube?

 

[landtank]

Rick, are those drawings to scale or just to illustrate the point. Also are the black circles supposed to represent the tires/axle tube with the center being the center of the axle tube?

The round circles are approximate size of the diff housing and the "T" section is approximate to the pinion flange. The lines for the drive shafts are the approximate length and the relationship between the t-case and diff pieces was a best guess.

So in short it was more of a drawing to illustrate what I couldn't effectively put into words. It's not meant to accurately depict the actual difference between the two systems.

It seemed like the idea that both our plates yielded identical results and it was just a matter of choosing the one that was easier to install. I just wanted it to be clear that it wasn't the case and there are subtle differences between the two and those differences can effect the outcome.

I will not dispute that my plates are more of a PITA to install than yours. I'm doing my 4th set next weekend and it has gotten much easier for me with practice and a helper goes a long way in speeding up the process. If people have concerns about being able to install my plates then they should seriously think about the consequences of not being able to complete the task and how that will effect their transportation needs.

 

[landtank]

Why would Rick's system keep the spring perches more level than any other axle rotation system?

It goes back to what we just talked about with the operating angles. My plates maintain the axle's position on the arm. The other solutions move the axle toward the rear of the truck. That rearward movement will throw the alignment of the spring perches off and can produce an interference problem between the spring and the bump tower.

This condition is not unique only to the options that we are talking about here. I had someone with MAF drop brackets with this same problem contact me earler this year.

The problem manifests itself when the weight of the truck is not quite enough to produce enough bow in the spring to clear the bump tower. That is why some people don't have a problem at all and others do and need to address it.

 

[sleeoffroad]

The round circles are approximate size of the diff housing and the "T" section is approximate to the pinion flange. The lines for the drive shafts are the approximate length and the relationship between the t-case and diff pieces was a best guess.

Ok, but then the picture is incorrect since the pinion does not point to the center of the axle housing, it is in fact higher. Also the distance that the diff is moved back is over exaggerated in relation to the rest. There is no way the pinion is moved back approx 2/3's of the axle tube thickness.

The drawing does illustrate the point. It also illustrates that if you move the transfercase down, then the operating angle will change at the diff end and what you show now for the red line being non-optimal will become optimal and the other not.

So in short it was more of a drawing to illustrate what I couldn't effectively put into words. It's not meant to accurately depict the actual difference between the two systems.

I can see it illustrating the point, but the effects is exaggerated. I will take some time and do a drawing trying to get as close as possible dimensions. I might need some info on your end as to how much the back and front holes are moved. Feel free to PM if you have hose.

It seemed like the idea that both our plates yielded identical results and it was just a matter of choosing the one that was easier to install. I just wanted it to be clear that it wasn't the case and there are subtle differences between the two and those differences can effect the outcome.

Yes, I agree that the results are not equal, but I am interested in the rear changes to see how much they are. However I hope you agree that for a given caster result (not amount of correction) the pinion angles has to be the same. It is only the position of the pinion in space that changes.

I will not dispute that my plates are more of a PITA to install than yours. I'm doing my 4th set next weekend and it has gotten much easier for me with practice and a helper goes a long way in speeding up the process. If people have concerns about being able to install my plates then they should seriously think about the consequences of not being able to complete the task and how that will effect their transportation needs.

Yes, we have always tried to make products that is easy to install and require minimal drilling etc. That caters for a certain customer. Yours does for another customers. However I think this thread is useful in illustrating differences in how things are done, and maybe how caster and pinion angles are coupled.

 

[sleeoffroad]

It goes back to what we just talked about with the operating angles. My plates maintain the axle's position on the arm.

Fore and Aft, however again for a fixed caster number our spring perches and yours will be at the same angle at a static ride height. Spring perches are also welded on the axle the angle can not change with caster. The issue is that the spring perch angle is changed in relation to the two mounting holes in the bushings on the control arm. So when the arm goes through it's sweep when the axle articulates, that is when things act different.

The other solutions move the axle toward the rear of the truck. That rearward movement will throw the alignment of the spring perches off and can produce an interference problem between the spring and the bump tower.

I think we are saying the same thing, but I do not think it is as much the rearward movement as the relationship of the axle housing to the control arm.

Also important to note that this does not happen with stock bump stops but becomes an issue when you install a bumps stop puck. We are looking into providing a puck that can bolt to the bottom of the spring perch, thus eliminating this issue. However a spacer on the bottom spring perch is more complex to install.

This condition is not unique only to the options that we are talking about here. I had someone with MAF drop brackets with this same problem contact me earler this year.

quote]
The problem manifests itself when the weight of the truck is not quite enough to produce enough bow in the spring to clear the bump tower. That is why some people don't have a problem at all and others do and need to address it.[/QUOTE]

 

[sleeoffroad]

OK, spent some time this morning to take measurements and drawings.

The first is a drawing showing the axle housing from the side. The red is the axle bracket that the control arm bolts to. The Yellow is the axle housing. The gray is the pinion and the blue is the pinion flange. The relationship of the bolt holes where the arm bolts to, axle center line, pinion position, pinion angle to bracket angle and pinion distance from axle center line is all to scale as best I can measure it.

The wireframe shows how the axle is rotated when the Slee caster plates are installed and it is rotated around the back bolt. The amount of rotation is correct based on our design of the caster plates.

The next is a blow up of the pinion area showing the measurements. The one we are intersted in is the backward movement. This shows the center of the pinion to have moved back .49"

This is the same sketch with the axle rotated around the center as Rick does with his caster plates. The rotation of the axle was set to the same as ours (since I do not know how much he rotates).

This is the overall drawing

and this is the detail close-up

From this you can see that the pinion actually moved back .33" So the total difference in pinion movement is 0.16". That is less than 3/16 of an inch. One could debate a little as to what direction the movement is measured in, but I think this is clear enough that there is very little movement difference between the two methods.

It is important to remember that this only shows what happens with the axle housing in relation to the arm in free space. To model the complete effect, one has to add the control arm and the mount to the frame on the vehicle. This will affect the net movement of any of the components.

 

[bpassmore]

Dadgum. that is some cool work Christo. thanks!

 

[Ebag333]

Post removed.

Nevermind, Christo threw me off by using wire frame for one, then switching for the other.

 

[Tapage]

thanks Christo .. excelent for us ( or me .. ? )

 

[Darwood]

Also important to note that this does not happen with stock bump stops but becomes an issue when you install a bumps stop puck. We are looking into providing a puck that can bolt to the bottom of the spring perch, thus eliminating this issue. However a spacer on the bottom spring perch is more complex to install.

Is there a reason to not provide a solution that uses the outside frame bumpstop mounting points that are similar to the rear bumpstops?

Oh and for the record, I like the arm method of caster correction.

 

[sleeoffroad]

Is there a reason to not provide a solution that uses the outside frame bumpstop mounting points that are similar to the rear bumpstops?

Not really. Other than cost. One would have to supply the spacer as well as the bump stop to most people. I do think the rubber snubber inside the coil (or otherwise known as Alf's Nose) is a better bump stop since it seems to act a little like a progressive stop.

Oh and for the record, I like the arm method of caster correction.

So do I .

 

[sleeoffroad]

I did two more drawings.

The 1st is based on using our 3 degree bushings, and installing them as per the instructions so that it rotates the axle around the center point between the two mounting holes.

Now rotated around the center of the axle tube.

As you can see the differences in how much the pinion is moved is very little. 0.388" vs 0.286"

 

[Cj80cruiser]

What tha..........I'm gonna have to chew on this for a few days before I get it.

 

[bpassmore]

this is great information.

 

[landtank]

I see you've been working with solid works, nice drawings.

 

[sleeoffroad]

Thanks. I want to put the arms into the equation as well and then see what happens.

 

[TrickyT]

Christo, Your drawings are enormously helpful in understanding the subtle geometry differences in the two approaches to caster correction. I'm sure they were time consuming to produce. Thanks for taking the time to do this. The light bulb that went on for me in seeing these illustrations, which of course I was aware of but had somehow neglected to consider in my thinking about the issue, is the fact that the axis of the front pinion does not intersect the center of the axle tube but rather above it. When you then apply caster correction, that vertical difference accounts for the greater difference in horizontal movement of the pinon flange compared to the relatively small change in horizontal movement of the axle. I get it now!