Ack's FAQ The Six Inch Rule

The Six Inch Rule

by Tim Tackett

(Note: The contents of this page originally appeared at North Coast Offroad's website, northcoastoffroad.com. Unfortunately, the site is no longer on the Internet. This article is a reconstruction of that page.)

While the Samurai suspension is easily modified to add lift, it does have some limiting factors associated with it. The stock Samurai drivetrain is limited to 6" of suspension lift (+/_ about 1/2" depending on spring condition). Beyond 6", the stock driveshafts start causing problems for highway usage and offroad with the amount of axle droop that you can achieve, primarily in the front. There is a reason why most Samurai lifts are between 4.5" and 5.5".

The rear driveshaft U-Joint angles become so miss-matched that you will start experiencing constant vibration at highway speeds. At low speeds, the T-case shifter will act like it is trying to come through the floor when rolling through second gear or under hard acceleration in any gear. On my personal truck with 8" of lift, I was going through a U-joint every three months at the T-Case rear output shaft and the rear lower pinion joint about every 6 months.

In the front, you simply run out of driveshaft droop as the upper T-Case U-joint yoke will bind on itself or the slip yoke body will hit the cross member. Both will occur at nearly the same point, so simply grinding out the yoke or cutting out the cross member isn't going to help to any significant amount.

Drive shaft spacers, extended slip yokes, or modified length driveshaft tubes, work great to add needed length, but none of these do anything to address the U-joint angles or binding when going with over 6" of suspension lift. A lot of vendors never mention this to their customers. We have seen written ads by one vendor for 7" and 8" SPOA suspension kits that include big 1.5" spacers to "correct perfectly for the lift height and allow for maximum flex on the trail". They also state "This suspension system not only makes your vehicle look like an offroad monster, it performs like one as well". There is probably more truth in that statement than meets the eye. I run an 8" lift suspension (not theirs!), and believe me, without addressing the driveshaft problem, you would have a real MONSTER on your hands!

With 8" of suspension lift and the truck parked in the driveway, the front driveshaft would be very close to being locked up at the T-Case. The rear U-joint angles would be so mis-matched that there would be a tremendous amount of vibration in high range. The stock driveshafts just cannot tolerate such angles, and they were never designed to. Basically your truck would be unusable except for smooth highway usage. We don't sell driveshafts, so this isn't some sales pitch to sell you one. It is intended to provide you with the truth as to what you should expect. If your going to go big with over 6" of suspension lift, then you need to budget for a pair of aftermarket driveshafts.

A lot of people will combine a suspension lift with a body lift. For liability reasons, none of the manufacturers of body lifts or suspensions recommend this practice, so neither can we. Body lifts do just that, they lift the body away from the frame providing additional tire clearance. They do not provide any advantages that are realized from a true suspension lift, nor do they have any impact on driveshaft angles. You have to decide what is right for you and your budget.

The most popular body lifts are the 1" and 2" versions. The 3" body lift is more difficult to install, and causes problems with the fuel filler neck hose, and the clearance in the body pan for the transmission and transfer case shifters. A lot of people also do not like the large amount of open space visible between the frame and body, but this could be filled to provide a visual barrier.