Over the axle panhard bar discussion...

[monkeyevil]

There has been a lot of talk about relocating the track bar over the axle when converting to an over the knuckle drag link setup. This has came up often with our OTK steering kit, but also with other companies steering setups, high steer knuckle swaps, etc...

Ofter you will hear that the drag link and track bar need to be parallel, and that is half true. The other half is they need to be similar lengths, (and to a point similar starting points) You could have a 32 drag link, and a 10" track bar mounted parallel, but they are going to move at VERY different arcs on bump and droop.

So at any rate this weekend Haleyes was up and I went about installing his OTK 1-ton steering, and an track bar relocation bracket we have been working on. I've never had a real issue with OTK steering installs and stock track bar locations, except for clearance issues between track bar and tie-rod in some setups; but the demand seemed to be there, so I wanted to verify the process.

So while mocking up the bracket and the tie rod, I quickly noticed that from the drag link mounting hole in the tie rod, to the new axle end track bar center was about 8". The pitman arm center to frame side track bar center was more like 4". Even with parallel angles I wasn't comfortable with a 4" difference in length.

The axle side track bar end couldn't be moved any closer to the coil spring, but since Hale doesn't run a sway bar, the frame side could be moved both up and out. So I chopped his bracket up raising the hole 1" and moving it out 2.75". Clearance on the coil at this point was tight, but manageable.

What I ended up with was a 32.75" drag link, and a 31.75 in track bar, near parallel angles, and a significant loss of time :laugh3:

So what does this mean? IMHO the angle to length relationship is closer leaving the track bar under the axle that it can be without out boarding the frame side mount when going OTK on a stock type knuckle, or mounting the drag link UTK on a WJ upper knuckle. Mounting a TRE or heim on top of a WJ knuckle, or on top of a highsteer arm IMHO will require out boarding the frame side mount. While thinking this through, I also realized that while parallel bars of equal length will move on the same arc if the movable bar they are attached to moves parallel to the unmovable one (axle to body) no matter where they are attached (distance apart); if they don't start from the same point if that object moves oddly (flex) they can still move in different arcs. Thank God I don't build race cars for a living or i would have a brain aneurysm.


Hales current setup.

An approximation of his angles with a stock located axle end, and a standard drop track bar bracket.

Looking at the picture of my wifes WJ setup bring an interesting counterpoint to this...

Her drag link is probably 3" longer than her track bar, yet her jeep has very little bump steer. I assume this is because of the shallow angles from a pretty small lift.

I don't know if this has been covered before, but I wanted to type it out while fresh in my mind. Your thoughs?

 

[ChiXJeff]

Spot on, man.

I have an O.R.G.S. fab-yer-own trackbar, with the HD bracket refit kit. Steering is a crossover Heim, not OTK. The angles on the draglink and the trackbar are almost perfectly parallel, but the trackbar is significantly shorter. My XJ does tend to dodge a bit under hard acceleration, and under braking. Were I to build up a new trackbar, with a modified bracket that would lengthen the trackbar, I'd probably have better road manners.

 

[monkeyevil]

Just did some quick calculations using circles in cad.


Using a 13 deg drag link angle and a 16 deg track bar angle with the same length (32") just educated guessing based on the photo.
The suspension compressing 2" causes a .4103 shift to the passanger side of the axle (caused by the trackbar) while it only causes a .3334 shift of the drag link axle side end. This will need a 0.0769 correction in the pitman arm to remain going straight.
The suspension drooping 2" causes a .4779 shift to the driver side of the axle (caused by the trackbar) while it only causes a .4103 shift of the drag link axle side end. This will need a .0676 correction in the pitman arm to remain going straight.

Using both a 13 deg drag link and track bar angle, with the track bar being 4" shorter than the drag link.
The suspension compressing 2" causes a .2917 shift to the passanger side of the axle (caused by the trackbar) while it only causes a .3334 shift of the drag link axle side end. This will need a 0.0417 correction in the pitman arm to remain going straight.
The suspension drooping 2" causes a .3590 shift to the driver side of the axle (caused by the trackbar) while it only causes a .4103 shift of the drag link axle side end. This will need a .0513 correction in the pitman arm to remain going straight.

Here is my cad drawing if your bored.
http://www.evilmonkeymedia.com/dl/trackbarangles.dxf

Red arc = 28" length
Blue arc = 32" length
Green line = drag link at ride height
Purple line = unparrallel equal length panhard bar at ride height, drag link at 2" droop.

 

[monkeyevil]

So it looks like drawing it out proves that at least at 13 deg a 4" difference in length is slightly better than a 3 deg difference in angle.

I tried a 16 degree drag link angle, and a 19 degree track bar angle and that has very similar movement on droop as a 4" shorter track bar at 16 degrees, but more movement on compression by .0163.

I wish I had a way to quantify what each distance at the pitman arm feels like at the wheel...

 

[dgrigorenko]

i think you are dead on man, and thanks for posting this in a clear manner. i had searched around for along time and didnt find anything on it in here, but i knew just by thinking about it that optimally both should be the same length and angle. currently my solution is fabbing a knuckle bracket that moves the draglink mount point. i have a thread up on it somewhere.

it would be interesting to find out how much pitman arm movement results in x distance of steering wheel rotation.

 

[monkeyevil]

Wait I guess I can.

XJ's come with a 2.4:1 variable ratio steering box. I'm going to assume this 2.41 ratio is on center which is hopefully how your driving down the road.

A .05 correction at the pitman arm will result in a .525 change of angle of the pitman shaft with a 5.5" c to c pitman arm. Multiply that by 2.4 and you get a 1.26 degree change in the wheel.

Can someone better at me with math verify this?

 

[monkeyevil]

Wait that math is wrong... Saginaw variable boxes are like 13:1.... I need to research that a little more.