Dear Tom and Ray:
I have a 2001 Toyota 4Runner with 160,000 miles. I also have a pop-up camper that I pull on occasion with the 4Runner. I just made a trip from Colorado up to Minnesota pulling the camper. The last 20 percent of the trip, when traveling on the interstate, the 4Runner started bouncing pretty good — so much that my daughter thought she was riding the horsey ride at the grocery store while riding in her car seat in the back. I jumped up and down on the hitch to the 4Runner and it continued to bounce a couple of times before stopping. Do I need new shocks? —Keith
Ray: Well, let's assume you've already checked the tires, Keith, to make sure they're not overinflated.
Tom: Wait! Let's not assume! Keith, check the tires, including the trailer tires, to make sure they're not overinflated, because that's a very common cause of bouncing and poor ride quality.
Ray: But if the tires are inflated correctly, then it sounds like you do need shocks. Here's the test. Unhook the trailer. Then put a foot on the rear bumper and stand up on it, holding on to the roof rack for support.
Tom: Then start bouncing up and down on the bumper. Get it really rocking — up and down, up and down, as far down as you can make it go.
Ray: My brother finds it helps to grunt like a gorilla and scratch his armpits while doing this.
Tom: Once you've got it really going up and down, then, when it's at the bottom of the cycle, hop off.
Ray: The bumper should come back up to its normal position and stop dead in its tracks. There shouldn't be even a hint of another oscillation.
Tom: If the truck continues to go up and down at all, you need shocks. Bad shocks certainly could cause the kind of bouncing you describe.
Ray: As you might imagine, this isn't very safe, Keith. When you bounce up, you're not only lifting the weight of the vehicle off of the rear wheels, which compromises your handling, but you're also stressing the trailer hitch. After a while, that thing could break, and the trailer could end up in a different lane from the 4Runner.
Tom: So get the shocks checked and, if necessary, replaced right away.