Jeep Wrangler YJ Driveshaft Replacement - Off-Highway Why-JPosted in Project Vehicles on July 1, 2009 0) (
Last month we covered the installation of a Rubicon Express 2.5-inch uspension system on our '89 YJ. We actually got over 4 inches of lift in the front and over 3 inches in the rear thanks to the Jeep's light weight and the longer 5-inch Rubicon Express shackles (stock is 4 inches).
Along with the additional 1/2-inch of lift, the longer shackles did a few things for us. The rear boomerang shackles raised the pinion angle and allow the longer springs to grow upon compression without binding. The front shackles prevent shackle inversion when the suspension drops out, but raised the pinion angle and reduced caster, slightly increasing on-road wander. The cure is to install some 2.5-degree shims to get the caster back, but most shims we've come across are aluminum. We'll hold out until we can get some true bolt-on steel units.
We ran the Jeep with the stock rear driveshaft for a couple hundred miles before upgrading the T-case to a JB Conversions Super Short Slip Yoke Eliminator and Tom Wood's Custom Drive Shafts 1310 rear CV shaft. The Jeep was drivable with the stock rear shaft and no T-case drop, but the rear pinion would bind at full droop and the Jeep had muy horrible vibration upon deceleration or coasting. Along with the Tom Wood's shaft, we installed a set of Rubicon Express 8-degree steel shims on the rear spring packs to angle the pinion more in line with the driveshaft. The 8-degree shims almost did the trick, but we still experience slight vibrations upon deceleration. We're going to leave it alone for a while to see if the rear suspension settles any more, which would lower the driveshaft angle in line with the pinion.
As for the steering, we ordered a Rubicon Express dropped pitman arm, but haven't installed it yet because our Jeep has a manual steering box and Rubicon Express arm is for a power box. The two aren't interchangeable. We've been running the stock pitman arm, drag link, and track bar. Although the steering wheel isn't centered, we didn't experience any bump steer with the track bar hooked up, but we did note some loss of front flex and a bit of harshness, so we removed the track bar. With it gone, the Jeep now has slight bumpsteer, but it's nothing too severe and we can live with it until we swap to a power steering box with the dropped pitman arm.
Off-road, we can tell the springs are still breaking in. With so little weight, it's tough to work them loose, but we notice flex improving with each off-road foray. Although the springs have a noticeable arch to them, the ride is moderately soft. We'll call it firm, yet forgiving. The gas-pressurized Rubicon Express monotube shocks aren't harsh in the small stuff, but really soak up the big hits when the going gets fast and rough. The couple times we've gotten the tires slightly off the ground we've been pleased with the softness and controlled nature of the landing. All in all, we're very happy with our suspension. We'll keep working away at breaking in the springs and beating the Jeep mercilessly off-road every chance we get.