I am getting ready to rebuild with gears, locker, etc. a D30. I read a thread somewhere about setting the pinion angle correctly then setting the steering knuckle angle to correct castor. Can someone direct me to that thread or explain that relationship for me please.
Link to castor / pinion chart that another JF member directed me to a while back. Previous comments about pinion first apply, but you may have to compromise at some point and dial the pinion back. If you do, do so in small increments and check for vibrations.
The whole "pinion over caster" thing is BS and certainly doesn't apply to all situations. Even with how low my rig is, the required pinion angle is still fairly high due to my flat belly. If I ran the pinion inline with the drive shaft, I'd be at about 3* caster with my HP30.....that little caster feels like ****. I run the pinion a few degrees low and run 6* of caster. Steering is great and I've got no driveline vibes.
Caster depends fully on tire size.
Larger tires will give the same trail numbers that result in good handling with much lower caster angles.
3-4° should be nearly perfect for a 37", I'd expect 6° to be excessive.
I ran 4 on 35's and will have roughly the same on 37's. It returned to center well and didn't go crazy following the crown.
'97 zj 5.2, some stuff, some other suff, and some things that even work sometimes.
3* felt like crap to me on 37's, 6* feels excellent. I'm sure 5* would be fine as well but I wouldn't want to run less than that. I know that, on paper, larger tires requiring less caster to give the same results makes perfect sense. But I've not found that to translate well to actual use.
Thanks slmason. I believe thats what I'm looking for. I am changing gears and will have an extra diff out of the jeep building it while I'm still driving my current set up. I guess my whole thinking behind this question is will I need to change the spring perch locations on the front like I am on the back and I wasnt sure if I needed to rotate the knuckles when I did this or not.
Thanks for the replies
Caster depends fully on tire size.
Larger tires will give the same trail numbers that result in good handling with much lower caster angles. 3-4° should be nearly perfect for a 37", I'd expect 6° to be excessive.
If you do the math, which I'll leave out here...
The center point of the spec range for caster for my '93 YJ is 6.3°.
1) Assuming that is for the stock 29" OEM tires, that puts the tire's ground contact point 1.6" in front of the axle.
2) A 35" tire needs 5.3° to put the contact point in the same place.
3) A 37" tire needs 5.0° to put the contact point in the same place.
I know my YJ with 35's is all over the road with the caster at 3.3°. I plan on moving the perches to fix it soon.
OK, after doing a bit more reading on this let me see if my plan seems right to you guys in the know. First off I'm not running an extreme amount of lift so I'm not sure I am going to "need" to turn the C's at all but if I do this axle I only want to do it once so I will probably go ahead and get it as close as possible. Right now I'm on 33's with a total of 4" of lift but I might go up to 35's at some point so I figure it will be a little more needed then, and I should be very close if I do this now.
1. Strip spring perches and shock mounts.
2. Figure correct pinion angle
3. Cut out and set C's at about 5.5-6.0 degrees
4. Trial fit, adjust, and weld up if good.
Does this sound right or like overkill? Also does anything change if I decide to upgrade to TJ axles with this. My D30 is 27 spline right now. Are the TJ axles also 27 spline or different?
@JeeperDon- if you just move your perches to set castor are you planning anything for pinion DS/angle or just prioritizing castor over pinion. Mine is a semi DD so I really prefer both. I also dont want any shims in when I am done with this.