Can someone tell me if I'm understanding this correctly. I got new CV driveshafts (I think that's the correct terminology, 2 u-joints up by T/case) 1310 front 1350 rear and a 4.5" lift.
Rear Axle 10 degrees
Pinion 84 degrees or 6 degrees up
T/case 86 degrees or 4 down
Front axle 10 degrees
front pinion 89 degrees or 1 up
T/case 86 degrees or 4 up
So I'm thinking the first thing I need is adjustable lower control arms (I have rear uppers only), already thinking about new kit. I understand I should plan the rear to rotate 2 degrees more up under driveload so in order to get zero angle I should rotate it up about 2 degrees taking into account driveshaft will change slightly.
On the front I think I read it will rotate down 2 degrees so right now I have an operating angle of 9 degrees plus 2 meaning I should rotate the pinion up almost 11 degrees ( I guess more like 9 or so given the driveshaft will also change).
This seems a bit extreme on the front, my castor angle looks to be about 7 right now and I'm wondering if I'd get any oil into the outer pinion??
Any help please.
In the rear you want 1-2 degrees LESS angle on the pinion so that when under acceleration the pinion nose lifts it INCREASES the angle to around zero difference. In front is where the JK bugaboo lives. You don't have to concern yourself with pinion angle shift up front because it's not going to be under constant torque loads like the rear. A stock JK front housing has about 6 degrees of offset between caster angle and pinion angle. If you set the caster at the stock max of around 4.5 degrees, it only leaves 1.5 degrees of pinion angle. While that's close enough on a stocker, add 4.5" of lift and 5 degrees of caster as many suggest and you'll only have one degree on the pinion and almost certain vibration issues to one degree or another.
As suggested above, there are some workarounds. One suspension vendor told me they'd had good luck setting caster at 3 - 3.5 degrees. That never worked on mine (see my sig for spec). Custom housing manufacturers like Dynatrac or Teraflex offer 10 degree offsets, which means five on the caster leaves five on the pinion, usually nailing the driveline / pinion angle and eliminating the vibrations. Guys that are handy with an angle grinder and welder have removed the inner "Cs" and re- welded them at the proper angles accomplishing the same thing. Tricky business, but could be done at the same time as a truss or sleeve & gusset job.
On mine I opted to install Spyntec manual hubs, which get the job done but really aren't cost effective, as you have to change all four axle shafts, front u-joints and convert to 5x5.5" wheels. I installed them before the manufacturers had the angle-corrected housings available, plus I'd already invested in Pro Steer ball joints and a sleeve & gusset job, so I wanted to retain the stock housing as long as possible. If I had it to do over again I wouldn't invest a dime in the stock housing, I'd just get a Pro Rck 44 and be done with it. YMMV, of course.
'09 JKRU. 4" Teraflex long arm, Teraflex R44 housing, Teraflex / Fox Resis, Poly Performance skids, Nemesis Billy Rockers, Nemesis flares, 37" ATZ P3s on 17" 5x5.5" Trailready HDs, Spyntec hubs, Teraflex BBK, Mopar BBK master/booster, Superior front & Alloy USA rear axle shafts, CTMs, Reids, Synergy drag link & tie rod, WTOR hydro-boosted steering, 5.38s, TF Dual Rate front bar, TF bumpers, Warn Powerplant, Tom Woods shafts, AA xfer case cable, Kilby canister relo, RH4x4 cage.