Pitman arm "what if"

[AndyG]

I hope @mrblaine posts on this -

What if you have a dropped track bar mount , and a dropped pitman arm and these angles ..the track bar is at 15 degrees and drag link at 10 best you can tell, so drag link can come up some ...

And you kept the welded on lowered Rough Country track bar mount and installed a stock pitman arm ...is there any benefit ?

Just asking , I realize it may be stupid , and the Jeep drives better than any lifted TJ I have ever driven.

Just wanting to learn


Andy G

 

[Goatman]

Dropped pitman arm mount? You mean you lowered the steering gear box? And THEN added a dropped pitman arm? Why would you do such a thing? Put the gearbox back on the frame where it belongs. That has to be one of the worst ideas EVER.

 

[AndyG]

Dropped pitman arm mount? You mean you lowered the steering gear box? And THEN added a dropped pitman arm? Why would you do such a thing? Put the gearbox back on the frame where it belongs. That has to be one of the worst ideas EVER.

Sir I don't think you understand the scenario I'm describing.... I edited my post to describe it better...bad job on my part.

A dropped track bar mount and dropped pitman arm.. that belong together... I'm just wondering what would happen if you had diverging angles and you went ahead and raised the pitman arm and drag link back to stock.

A little bit of the story is the way the track bar is made it depends on where you put the angle finder.

 

[Lou]

How are you measuring the angle of each bar? Neither bar is straight so sticking an angle finder on it is useless.

 

[AndyG]

How are you measuring the angle of each bar? Neither bar is straight so sticking an angle finder on it is useless.

Agreed... I just admitted that in an earlier edit .. so throwing that out the window if I raised the drag link back to the stock elevation and kept the track bar lowered at the frame mount what would be the consequences .

 

[BuildBreakRepeat]

As long as the angles from a straight line mounting point to mounting point are the same - you will not have bumpsteer. You do lose uptravel most of the time by running a dropped mount though

 

[Lou]

Ive never done this, but I would think the easiest way to determine the slope of each bar would be to measure from level ground up to the center of each joints pivot point. You can then use those measurements to determine the slope of each bar.


OR, If you know the TB mount is dropped X inches.... and the drop pitman arm is dropped X inches... Then that should tell you if you are ok or not.


OR, if it drives fine why even bother?

 

[AndyG]

As long as the angles from a straight line mounting point to mounting point are the same - you will not have bumpsteer. You do lose uptravel most of the time by running a dropped mount though

Now this is a good post.. Chris be sure to put this guy down for bonus points and make sure he gets one of the t-shirts.

Again I'm not really trying to fix something that isn't broke... My goal is to understand TJ steering at the highest level I can..

I'm also a believer in you have to know the rules before you break them.

I like the idea of pulling a string from point-to-point and just knowing what my angles are.

Also when you have an oddball configuration like this... Makes me wonder despite the fact that it drives good.... Is there something in this setup that is less than optimal?

Again I'm just trying to understand.

I don't always have to know the technical side of everything to appreciate the benefit... But I have really pushed myself to understand the different steering setup some of these and what's going on...and why.

And I'm trying to increase that knowledge... Even if it's knowledge as to why not to do something.

 

[BuildBreakRepeat]

Now this is a good post.. Chris be sure to put this guy down for bonus points and make sure he gets one of the t-shirts.

Again I'm not really trying to fix something that isn't broke... My goal is to understand TJ steering at the highest level I can..

I'm also a believer in you have to know the rules before you break them.

I like the idea of pulling a string from point-to-point and just knowing what my angles are.

Also when you have an oddball configuration like this... Makes me wonder despite the fact that it drives good.... Is there something in this setup that is less than optimal?

Again I'm just trying to understand.

I don't always have to know the technical side of everything to appreciate the benefit... But I have really pushed myself to understand the different steering setup some of these and what's going on...and why.

And I'm trying to increase that knowledge... Even if it's knowledge as to why not to do something.

That’s a good mentality to have. If you let go of your steering wheel when going over a speed bump from straight on, does the wheel move any? If it does (even a little bit) that can be dialed out. Sometimes bumpsteer is more noticeable depending on how close the angles are to each other - I’ve used the string method to confirm mine many times. The Tj stock steering is not perfect, given that when anything is moved from stock the length and well as the mounting location can change. The closest you can get to those two angles and lengths being equal, the better the steering will feel.

 

[Chris]

What if you just installed a Rough Country long arm along with this pitman arm setup you're proposing and called it a day?

 

[AndyG]

That’s a good mentality to have. If you let go of your steering wheel when going over a speed bump from straight on, does the wheel move any? If it does (even a little bit) that can be dialed out. Sometimes bumpsteer is more noticeable depending on how close the angles are to each other - I’ve used the string method to confirm mine many times. The Tj stock steering is not perfect, given that when anything is moved from stock the length and well as the mounting location can change. The closest you can get to those two angles and lengths being equal, the better the steering will feel.

If it has any at all , it's pretty close to minimal I was actually feeling for that yesterday.

What I'm suggesting is actually kind of the opposite of the cure for bump steer... Raising the drag link but keeping the track bar at the lower elevation since the mount is welded and is designed for the Rough Country track bar that I'm very satisfied with with my upgraded bushings.

I'm just curious what would happen if you put a stock pitman arm on with a dropped track bar mount.

 

[AndyG]

What if you just installed a Rough Country long arm along with this pitman arm setup you're proposing and called it a day?

Pervert.

Can't you see I'm trying to make this thing worse so I can figure out how to fix it again?

 

[BuildBreakRepeat]

If it has any at all , it's pretty close to minimal I was actually feeling for that yesterday.

What I'm suggesting is actually kind of the opposite of the cure for bump steer... Raising the drag link but keeping the track bar at the lower elevation since the mount is welded and is designed for the Rough Country track bar that I'm very satisfied with with my upgraded bushings.

I'm just curious what would happen if you put a stock pitman arm on with a dropped track bar mount.

Theoretically yes. Raising the mounting location of the drag link at the knuckle has the same effect on the angle as lowering the trackbar mount. You might run into issues with the drag link on top of the knuckle however. Right now, a dropped pitman arm is doing you better on the RC dropped mount.

 

[Lou]

Also when you have an oddball configuration like this... Makes me wonder despite the fact that it drives good.... Is there something in this setup that is less than optimal?

The less than optimal part would be the loss of up travel due to the drop track bar bracket.

 

[AndyG]

The less than optimal part would be the loss of up travel due to the drop track bar bracket.

K.

Would raising the drag link by putting on a stock pitman arm affect the travel or is the travel affected like it is.

I have an unreal amount of flex in both directions so I'm not too concerned about articulation.

I'm just trying to understand what would it change if you raised the drag link to stock.

 

[AndyG]

Pervert.

Can't you see I'm trying to make this thing worse so I can figure out how to fix it again?

Man you know I'm the poster boy for great performance with Rough Country . I'd be something on Wheels if I could get a hold of some quality stuff

 

[Lou]

How much up travel do you have?

I’m at nearly 6.5” up. My currie TB JJ is hitting the front diff cover/axle. If I was to drop the trackbar frame side mounting point, that would decrease my up travel.

I am jealous that you have an unreal amount of flex. My flex is real and understood given my shocks/bumpstops.

 

[Steel City 06]

Factory style steering can be visualized as a parallelogram.

The drag link and the trackbar make up the two long sides of the parallelogram. The knuckle and the frame act as the other sides of the parallelogram. (They are offset and even reversed, but in this case that doesn't affect the analogy). For this scenario, let us visualize the pitman arm as fixed. The knuckle is allowed to pivot.

As the suspension moves up and down, since the upper mounts for the drag link and the track bar hold the bars in the same pivot, the horizontal movement between the two at the other end is the same. Thus, no matter where the axle is in its travel, the parallelogram is maintained. Both the drag link and panhard rod are parallel, and the frame and theoretical knuckle are parallel. Thus, the knuckle does not pivot.

When that geometry is disrupted, such as when the mounting points for the trackbar or drag link are changed, the result is that the parallelogram is now a non-regular quadrilateral, or possibly a trapezoid.

Now, as the suspension moves up and down, since the lengths aren't the same, there must be an angular change between the knuckle and the frame throughout the suspension travel. Since the frame can't move, the knuckle must turn. (Alternatively, the pitman arm must turn.)


If you want to see this visually, take four pieces of scrap wood or something and build a rectangle with only one nail in each corner. As you flex the rectangle, it becomes a parallelogram. The long sides are like the drag link and trackbar, and the short sides are like the fixed frame/pitman arm and the knuckle. Holding one short side in place and moving the box up and down on the other end is like suspension travel. Rotating the short piece on one end is like turning the pitman arm.

Now take one of the short sides, and make it significantly shorter or longer. Hold one of the short sides in place, and move the other end of the quadrilateral up and down. Note that the other short side rotates with respect to the one being held down. This is bump steer. The simple act of moving the suspension must cause the knuckle or the pitman arm to turn.

 

[AndyG]

How much up travel do you have?

I’m at nearly 6.5” up. My currie TB JJ is hitting the front diff cover/axle. If I was to drop the trackbar frame side mounting point, that would decrease my up travel.

I am jealous that you have an unreal amount of flex. My flex is real and understood given my shocks/bumpstops.

I don't know I'm not with the TJ and I can't measure it. But I know it when it hits the bump stops I'm stuffed as much as I want to be and without even unhooking the disconnects I've got plenty of travel on the other side.

You know this doesn't call for that . . I'm just trying to learn something about steering geometry... I'm not having a battle of the builds. It works great I'm just asking a simple question that none of us guys don't know the answer to. ... What actually changes if you leave the track bar Lower and the pitman arm higher..are there consequences or does it matter.

I'm not trying to increase travel either way ..at full stuff I don't want them any closer.

Just a geometry question... If you want to pick a part what I'm saying that's fine. I never said anything about needing more Flex or wanting more... I'm totally happy I'm just trying to understand the consequences of a change that I haven't seen mentioned on this form before.

 

[mrblaine]

Factory style steering can be visualized as a parallelogram.

The drag link and the trackbar make up the two long sides of the parallelogram. The knuckle and the frame act as the other sides of the parallelogram. (They are offset and even reversed, but in this case that doesn't affect the analogy). For this scenario, let us visualize the pitman arm as fixed. The knuckle is allowed to pivot.

As the suspension moves up and down, since the upper mounts for the drag link and the track bar hold the bars in the same pivot, the horizontal movement between the two at the other end is the same. Thus, no matter where the axle is in its travel, the parallelogram is maintained. Both the drag link and panhard rod are parallel, and the frame and theoretical knuckle are parallel. Thus, the knuckle does not pivot.

When that geometry is disrupted, such as when the mounting points for the trackbar or drag link are changed, the result is that the parallelogram is now a non-regular quadrilateral, or possibly a trapezoid.

Now, as the suspension moves up and down, since the lengths aren't the same, there must be an angular change between the knuckle and the frame throughout the suspension travel. Since the frame can't move, the knuckle must turn. (Alternatively, the pitman arm must turn.)


If you want to see this visually, take four pieces of scrap wood or something and build a rectangle with only one nail in each corner. As you flex the rectangle, it becomes a parallelogram. The long sides are like the drag link and trackbar, and the short sides are like the fixed frame/pitman arm and the knuckle. Holding one short side in place and moving the box up and down on the other end is like suspension travel. Rotating the short piece on one end is like turning the pitman arm.

Now take one of the short sides, and make it significantly shorter or longer. Hold one of the short sides in place, and move the other end of the quadrilateral up and down. Note that the other short side rotates with respect to the one being held down. This is bump steer. The simple act of moving the suspension must cause the knuckle or the pitman arm to turn.

It is much easier to visualize and explain if you use arcs that should be parallel.

https://www.quadratec.com/jeep_knowledgebase/article-68.htm

That and Jeep violated one of the more prevalent rules in that both the draglink and trackbar should be similar in length since not doing so causes them to describe disparate radii. They compensated by running them slightly out of parallel.