Suspension clunk after Control Arm and Sway Link replacement

My 2006 Prius, with 240K miles finally got around to needing a bunch of suspension components replaced.

I started with the driver side lower control arm and sway bar link. A couple days later, I noticed a clunking sound start, intermittently happening once when starting pressing on the accelerator, and happening once when starting pressing on the brake. It is intermittent, sometimes a turn can encourage it, sometimes it doesn’t. It sounds as if something is moving between two positions.

After reading around, one possible reason for that could have been a bad CV joint: I could hear a faint clicking when paying attention at higher speeds at times, and there was a bit of play in the bar segment between the two joints. So I replaced the CV halfaxle. The problem continues. Maybe it wasn’t the CV joints, and I just noticed a pre-existing problem by being much more vigilant...

I also ended up doing all the same work to the passenger side, and after a day or two I’m hearing the same clunk now happening from that side. As before, a few hundred miles has caused the clunk to happen a bit easier and more reliably.

My current best theory is the LCA might be shifting between two positions as it encounters force in one direction or another. I’m pretty sure I torqued the two bolts on each LCA correctly (101 ft lb, with the suspension loaded/settled).

The only thing I can really think of doing is trying to torque the bolts down a bit farther. How far is too far? Is there anything else I should try to diagnose before going down that route?

It would be pretty easy to change the sway bar links back to see if that was the cause, but it doesn’t feel like that would be the case? Do the sway bar links get much in the way of stress when the car isn’t turning, even with slight applications of gas/brake?

 

I inspected as much of the left and right engine mounts as I could see without disassembling anything, no issues. The bottom engine mount looked fine. I don’t feel any unreasonable clunking during ICE start/stop, so I don’t suspect the engine mounts.

I swapped back to the original sway bar links. No change. I over-tightened 3 of the 4 control arm bolts to 110 ft lb (couldn’t get to the one that interferes with the oil drain pan). No change.

At this point the only thing I can think of is swapping back to the original control arm, but that’s more invasive than I was hoping to have to do. If that resolves the problem, I have no idea what would be wrong with the new control arm to try and fix it.

 

I used NAPA LCAs w/ ball joint assembly (although I’ve reproduced the problem with the original ball joint).

I don’t have access to a car lift, I’ve been using a basic trolley jack, a couple jack stands, and some large pieces of lumber to put the wheels on when needing to work under the car with the suspension loaded (I’ll get some ramps someday).

 

So I convinced myself that engine mounts were the problem, and finally got all 3 replaced. The start/stop clunk still happens. I guess I should probably take it into a shop at some point, as I'm out of ideas.

 

I actually did those first. They were in for several months before I also changed the control arms, and no problems during that interval.

 

I actually put the original LCA's back in temporarily and the clunk remained, so it's either another part, or Raphael's suggestion about the bolts being insufficiently torqued. I've never used loctite, but I have tried to torque them down somewhat beyond spec. I went 20 ftlb beyond spec, but that wasn't enough to resolve. I wasn't quite brave enough to go further.