Caster question

[Unitize]

Hi all,

I’ll preface this by saying I’m not the most mechanically inclined and learning as I go. I recently installed the Rancho geometry brackets on my 2014 Jeep JK that has a 4 inch lift. I was having issues with the Jeep being flighty and steering not returning to center and this seemed to be the best option for my budget. Once I installed the brackets I was getting a harsh driveline vibration so I removed the front driveshaft and that seemed to be the culprit (both driveshafts and all control arms are stock, I plan to upgrade once it’s in the budget). I was still getting a slight flighty feeling but the steering does return the center a lot better now, so I’m trying to figure out my caster. I’ve provided the measurements below but I’m still unsure what to make of them or if I’m even measuring from the right spots. Any tips or suggestions would be much appreciated, even constructive criticism. Thanks!

 

[Mopar]

Hi all,

I’ll preface this by saying I’m not the most mechanically inclined and learning as I go. I recently installed the Rancho geometry brackets on my 2014 Jeep JK that has a 4 inch lift. I was having issues with the Jeep being flighty and steering not returning to center and this seemed to be the best option for my budget. Once I installed the brackets I was getting a harsh driveline vibration so I removed the front driveshaft and that seemed to be the culprit (both driveshafts and all control arms are stock, I plan to upgrade once it’s in the budget). I was still getting a slight flighty feeling but the steering does return the center a lot better now, so I’m trying to figure out my caster. I’ve provided the measurements below but I’m still unsure what to make of them or if I’m even measuring from the right spots. Any tips or suggestions would be much appreciated, even constructive criticism. Thanks!


View attachment 131087View attachment 131088View attachment 131089

Do I see a caster angle of 10.1 or 10.7? If so, that’s crazy! That’s definitely affecting your driveline vibrations.

Get rid of the geometry brackets. Get adjustable lower control arms at a minimum. With a 4 inch lift you might need upper control arms too but you definitely need lowers.

Once you have adjustable lowers, get your caster angle to 5 degrees and go from there. I doubt I’d go above 6 degrees but run some tests till you are happy.

With a 4 inch lift you also need a new driveshaft. You could try a high angle Rzeppa joint but I would not. You need a double cardan joint driveshaft with that much lift.

Lifting a Jeep PROPERLY costs some money. You don’t have to spend thousands but you do need to prepare to spend in the vicinity of $1000 to get it right. How’s your axle alignment? Do you have an adjustable front track bar? What about the rear? You might look at maxpeedingrods control arms. I’m testing some right now. You can save a little money but I don’t know how the long term durability will be but they do seem to be well made. We’ll see

 

[Unitize]

Do I see a caster angle of 10.1 or 10.7? If so, that’s crazy! That’s definitely affecting your driveline vibrations.

Get rid of the geometry brackets. Get adjustable lower control arms at a minimum. With a 4 inch lift you might need upper control arms too but you definitely need lowers.

Once you have adjustable lowers, get your caster angle to 5 degrees and go from there. I doubt I’d go above 6 degrees but run some tests till you are happy.

With a 4 inch lift you also need a new driveshaft. You could try a high angle Rzeppa joint but I would not. You need a double cardan joint driveshaft with that much lift.

Lifting a Jeep PROPERLY costs some money. You don’t have to spend thousands but you do need to prepare to spend in the vicinity of $1000 to get it right. How’s your axle alignment? Do you have an adjustable front track bar? What about the rear? You might look at maxpeedingrods control arms. I’m testing some right now. You can save a little money but I don’t know how the long term durability will be but they do seem to be well made. We’ll see

Thank you for the feedback, I’ll definitely look at getting some adjustable control arms and the driveshaft is next on my list. I inherited this Jeep so I’m still finding things wrong as I go and trying to save up to get the proper parts. I also discovered yesterday that while the list I got with the Jeep said it was a 4 inch lift, it’s actually a 3. I moved the upper arms to the 3 inch slot and reattached the front driveshaft and the vibrations are gone. I remeasured the caster from where I understand you’re supposed to measure from and it’s still reading right around 10.7-11.3 depending on exactly where I place the angle finder. I was under the impression that you were supposed to subtract 6 front that with factory equipment so it would be 4.7-5.3, is that incorrect?

It does actually have an adjustable track bar, I’ll get back to you on the axel alignment and everything in the rear appears to still be stock. Thanks again!

 

[pc1p]

I remeasured the caster from where I understand you’re supposed to measure from and it’s still reading right around 10.7-11.3 depending on exactly where I place the angle finder. I was under the impression that you were supposed to subtract 6 front that with factory equipment so it would be 4.7-5.3, is that incorrect?

Caster is measured against true vertical. Assuming your angle finder was zero'ed out appropriately, it's very likely the cause of your vibrations. On a JK, caster angle and pinion angle share a fixed, inverse relationship. This is because the inner "C"s and differential housing are welded together as one solid unit. When you rotating the pinion up to reduce driveline vibrations, simultaneously reduces your caster, and vice versa. There is about a +6° difference between pinion and caster angles, and your measurements show this to be accurate for your axle. What this means is that you can estimate caster based off of pinion angle. Example: if you measure pinion angle to be 1º (how you measured it at least), you know that with +6°, you have ~7° of caster.

The best way to determine the "sweet spot" is to set your pinion angle to where it should be fine, and then confirm caster. You can generally go down to ~4°, though closer to 5°-5.5° is generally best for drivability. The larger the tire size you're running, the closer to 4° you can get away with.

It looks like you have aftermarket lower control arms already. These are usually longer (esp those meant for 4" lifts) to help with centering the axle and keeping caster in check. With the geometry brackets, they're too long, leading to your excessive caster measurement. You will likely want to go with adjustable lower control arms (and if you plan on keeping the 4" springs, adjustable uppers as well), though the geometry brackets are good if you don't mind how low they hang as they help with control arm angles.

 

[Mopar]

Thank you for the feedback, I’ll definitely look at getting some adjustable control arms and the driveshaft is next on my list. I inherited this Jeep so I’m still finding things wrong as I go and trying to save up to get the proper parts. I also discovered yesterday that while the list I got with the Jeep said it was a 4 inch lift, it’s actually a 3. I moved the upper arms to the 3 inch slot and reattached the front driveshaft and the vibrations are gone. I remeasured the caster from where I understand you’re supposed to measure from and it’s still reading right around 10.7-11.3 depending on exactly where I place the angle finder. I was under the impression that you were supposed to subtract 6 front that with factory equipment so it would be 4.7-5.3, is that incorrect?

It does actually have an adjustable track bar, I’ll get back to you on the axel alignment and everything in the rear appears to still be stock. Thanks again!

I have a 3.5 inch lift (actual measurement is closer to 3 inches) and it was on it when I bought it. It had a few things wrong with it as well when I bought it. They are all fixed now and it rides really well.

If you don’t have at least a track bar relocation bracket for the back axle or an adjustable rear track bar, the rear axle will not be centered. I’d get it back to where it should be….centered under the Jeep. Then, align the front to the rear.

I have 5* of caster measured at the ball joint and it drives and steers great.

 

[Mopar]

I did a screenshot of this from another site and it’s a good general guide to start from for lower control arms measurements.