Determining proper caster and pinion angle.

[BostonRubicon19]

I have a 2023 JLU Rubicon that has been through the ringer unfortunately with too many hands in the cookie jar, so to say.
Finally found a mechanic in Dundalk Md that knows his stuff.
I learned that 4wp would set my alignment to factory settings. And readjust all my control arms and steering.
Fast forward to current situation. I learned my both new pinion seals were leaking after changing to 4.88’s. Pinion angles were way off.
front was 11.1°, and rear was -5°.
Took it in to new mechanic. He had time to get my front end squared away to 5°. Jeep drove like a dream again.
upon fixing rear end alignment he went a little further and got both front and rear pinion angles to 4°. Been also dealing with my 4hi auto vibrating.
Took the jeep for a couple highway rides. Vibrations start over 45 mph. But alignment is perfect. It’s parked at this time.
Can 1° of caster really alter this vibration? I’m waiting for them to have time to drop it off.
Haven’t discussed if tires aren’t balanced and maybe a weight fell off or just that the 1° was too much.
4.5” fully adjustable suspension, including 2.5 ton steering, 4.5” MC springs, fox shocks, front and rear Tom Woods driveshafts, 4.88 Revolution gears, MC under cloak and pumpkin skids.

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[Maverick909]

caster is to low. i run mine at 6-6.5 degrees in the front rear hasnt been toched at all with zero issues. also that drive shaft seems to be out an awful lot if its sitting at ride height.

 

[BostonRubicon19]

caster is to low. i run mine at 6-6.5 degrees in the front rear hasnt been toched at all with zero issues. also that drive shaft seems to be out an awful lot if its sitting at ride height.

Do you know what your rear is at? I’m just trying to find a comparison. Can’t go by stock anymore.
the driveshaft used to be wicked compressed from my control arms shortening my wheel base. I sent in the pictures and measurements to Woods driveshaft and they said it was fine. Went back and forth with them for about an hour. With the 4HI auto issue was told to get the pinion at 4-5°. So I’ll try and see if I can get back to 5° and go from there. Trial and error. My goal of course is to kill the vibration because I’m gonna be driving to South Florida in March. And have 3 offroad trips coming up.

 

[Maverick909]

when i get my jeep back ... hopefully in the next day or two i can grab a measurement of the rear. or maybe @chevymitchell might be able to give you a better number. He Seems to be extremely knowledgeable about with jeeps and these kid of numbers off the top of his head!. lol if he doesnt reply before i get my jeep ill 100% grab you that caster number

 

[Buddy Lee]

My understanding on the rear is you center the axle, and then use the driveshaft to set the rear caster. 1-2 degrees is what I have researched. I would put an angle finder on the driveshaft near the rear pinion and adjust your upper control arms until the rear pinion angle and driveshaft are at 1-2 Degrees. I have some UD 60’s in my garage I will be installing soon on my Rubicon for new 38” tires. This is what I plan to do, as thats how I set up my 3.5 Metalcloak lift when I installed it. No issues at all. The front should be a minimum of 6 degrees and probably no more than 7 with a standard front axle or you will likely have a vibration.

 

[daverockville]

My understanding on the rear is you center the axle, and then use the driveshaft to set the rear caster. 1-2 degrees is what I have researched. I would put an angle finder on the driveshaft near the rear pinion and adjust your upper control arms until the rear pinion angle and driveshaft are at 1-2 Degrees. I have some UD 60’s in my garage I will be installing soon on my Rubicon for new 38” tires. This is what I plan to do, as thats how I set up my 3.5 Metalcloak lift when I installed it. No issues at all. The front should be a minimum of 6 degrees and probably no more than 7 with a standard front axle or you will likely have a vibration.

What is the pinion angle in the front for your setup?

 

[daverockville]

I am reading conflicting information on the threads. What should the pinion angle in the back be ideally or the range for a factory driveshaft with cv joints on both ends?

 

[Buddy Lee]

It’s a bit of a balancing game. Do you have fixed or adjustable controls arms. Do you have factory or after market axles with extra caster. Let’s start with a factory JL set up. They typically come with a castor setting in the range of 4.5 degrees. When you lift the Jeep it can affect the steering making a bit more flighty going down the road. To combat this you to bump the caster up to 6 degrees to make it more stable at speed. The problem is that the factory axle doesn’t have extra caster built in and adding too much can cause driveline vibrations at higher speeds because it puts the lower driveshaft yoke in to severe of an angle. Your factory axle should be good at 6 degrees as it’s been proven safe by many other jeepers, including myself. The axle fad system was designed to improve fuel economy but actually also helps reduce any vibrations in the front drive shaft by allowing it not to spin. If you develop a vibration problem just slightly back off the caster until it is gone. The vibration is typically at higher speeds and not when you are in low range. The rear is a bit more tricky. Ideally you want the shaft to be as straight as possible into the rear axle housing with an aftermarket driveshaft. The double cardan is designed to capture the angle deflection so you can keep the lower part of the shaft straight with the axle housing.
With a factory axle you will need to try and balance the angles between both sides to minimize a sharp angle at either end. Adam’s has a nice diagram. If you don’t have adjustable control arms I would definitely recommend it as you can’t make any angle adjustments without them.

 

[BostonRubicon19]

caster is to low. i run mine at 6-6.5 degrees in the front rear hasnt been toched at all with zero issues. also that drive shaft seems to be out an awful lot if its sitting at ride height.

Meaning like it’s too long? And the mechanic gave the wrong measurements to woods driveshaft?
Could you further explain what the issue you think is? Should I have a shorter driveshaft on the front?

It’s a bit of a balancing game. Do you have fixed or adjustable controls arms. Do you have factory or after market axles with extra caster. Let’s start with a factory JL set up. They typically come with a castor setting in the range of 4.5 degrees. When you lift the Jeep it can affect the steering making a bit more flighty going down the road. To combat this you to bump the caster up to 6 degrees to make it more stable at speed. The problem is that the factory axle doesn’t have extra caster built in and adding too much can cause driveline vibrations at higher speeds because it puts the lower driveshaft yoke in to severe of an angle. Your factory axle should be good at 6 degrees as it’s been proven safe by many other jeepers, including myself. The axle fad system was designed to improve fuel economy but actually also helps reduce any vibrations in the front drive shaft by allowing it not to spin. If you develop a vibration problem just slightly back off the caster until it is gone. The vibration is typically at higher speeds and not when you are in low range. The rear is a bit more tricky. Ideally you want the shaft to be as straight as possible into the rear axle housing with an aftermarket driveshaft. The double cardan is designed to capture the angle deflection so you can keep the lower part of the shaft straight with the axle housing.
With a factory axle you will need to try and balance the angles between both sides to minimize a sharp angle at either end. Adam’s has a nice diagram. If you don’t have adjustable control arms I would definitely recommend it as you can’t make any angle adjustments without them.

I have adjustable control arms. I also have Woods front and rear driveshafts. I have the factory D44 axles also. When I use 4Hi auto in inclement weather on the road, the vibration whether on the fly or from the beginning it starts to vibrate about 40mph and tapers off after 60mph.

 

[TrailMax]

Have you thought about either going to a *good* fabrication shop to cut and rotate the knuckles so you can have the correct caster and a good driveshaft angle, or see if you can get a new axle that already has the knuckle orientated to give you the correct angles?

Definitely wouldn't be cheap, but may save a lot of your headaches - and may also give you a good excuse to go with upgraded axles.

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