New trailing arms didn't fix rear clunk
 

I have a new to me '99 Boxster. 85k miles. The car is clunking in the rear at low speed over bumps. Reading old forum posts, it looked to be a classic symptom of worn trailing arms. I've now installed new ones (TRWs), but I'm still hearing the clunk. It may be a tiny bit better than it was before.

What should I check out next? To my knowledge, all the suspension is original.

Thanks for your help!

P.S. I don't know if this is related to problem, but the left arm was a lot more difficult to install than the right. My procedure was to screw the front bolt to the chassis and do the coffin arm bolt last. On the left side, the trailing arm did not line up well with the control arm—it was about 1/8 to 1/4 inch too short and required a bit of force to push the control arm and trailing arm toward each other to get bolt through the hole. The right side needed some nudging, but very little and was pretty easy to do. I don't know if this means anything.

sway bar bushings & links or rear struts

IIRC mine was the same way. And, like you, the sound got better but didn't go away. Pretty sure my struts are shot. I replaced the drop links at the same time I replaced the trailing arms. Sway bar bushings are on my list to replace as well.

Glad I'm not the only one, Radman!

I examined the sway bar bushings and links and with a pry bar I've not detected any play. How can I examine the rear struts? Which part of it would cause a clunk?

I haven't discovered it yet lol! I could tell a strut was bad when it was on a lift as the wheel/tire was pretty easy to move. I'm also guessing the mounting plate at the top could be bad/loose.

Well I believe I figured it out. I was smacking the trailing arm with my palm, seeing if I could get that to rattle, but I heard a rattle toward the bumper. Eventually I found that one of the bumperettes could be wiggled up and down. The bumperettes bolt to a reinforcement bar behind the bumper. I took the bumper off and, sure enough, the two bolts that attach the reinforcement to the frame were loose.

I have no idea how they got loose loose. Kind of disturbing, actually. Maybe it was a shoddy repair—during disassembly of the spoiler to get the bumper off, I noticed two of the three rivets that hold the spoiler trim had their centers knocked out already.

So it looks like I didn't need to do the trailing arms, but seeing how common an issue it is, it may have been inevitable.

I hope this helps someone!

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I'm trying to track down the same noise in my 01. Did that fix your problem?