The 1998-2007 LX470 and 2003-2008 GX470 both had variable height control systems (hydraulic for the LX470,air suspension for the GX470) that share a common problem: a thump, clunk or “kick from behind” when coming to stop or taking off from a stop.
The issue most commonly is from the rear driveshaft. This driveshaft passes power from the transfer case underneath the vehicle to the rear differential, which then splits the power to both rear wheels. Because the height of the vehicle can change depending on what the height control system is doing, the driveshaft needs to change length to accommodate the relative up and down motion of the transfer case and the rear differential.
While a driveshaft changing length is a required feature of vehicle with a live rear axle (the length change accommodates the suspension movement of the rear differential so the driveshaft doesn’t explode the first time you hit a bump), the GX470 and LX470 driveshaft requires more extension from the driveshaft due to the height control system. The height changes more, so does the driveshaft.
The driveshaft has a slip fitting (called the slip yoke) that allows this length change. There is a grease fitting designed to allow lubricate the plunging and extending motion, but even with sufficient grease the motion can stick. This sticking and releasing is the thump, clunk or kick you feel when it happens. Here’s a driveshaft with an extremely rusty slip yoke that was binding completely:
The grease fitting is highlighted. The grease would have helped prevent the binding, but not in all cases. Fortunately for the GX470 and LX470, Lexus has updated the rear driveshaft to help prevent this issue reoccurring, but periodic greasing of the driveshaft’s bearings and slip yoke is crucial to perform regardless.
As Minneapolis, Minnesota’s premier independent Toyota and Lexus specialist repair shop, CARspec can quickly identify a binding slip yoke and address the concern usually the same day. If you have a GX470 or LX470 with a thump, clunk or kick sensation, don’t hesitate to call us at (952)426-4798 to schedule an appointment today!