The Dreaded Shock Rattle

My 2017 is in the shop as I type this for the shock rattle identified by the 2016 TSB - there exists an superseded part # - I hope it's a lock nut of some kind. The service manager mentioned a "collar" that gets replaced as well. I bought my Gen 4 in Dec 0f '17 and it has 8200 miles on it. The rattle became a "thing" at about 7500miles.

While I can certainly do the repair myself - I want a record in the system and believe that it's in my best interests to have Toyota address this with "their" updated part. If this comes back in 7500 miles they will be on the hook.

 

Thanks a ton - your fix solved this problem!

I have been having this rattle since I bought my preowned 2016 Prius Four 3 years ago but lately it has started bothering me more often. So, during the alignment/balancing/rotation, I asked Firestone guy to diagnose the problem. He charged $25+taxes to look at it and gave me a quote of $700+ to replace the left rear strut mount and both rear struts plus labor. Luckily he didn't have strut mounts handy, so I made my way out easily and opened up the top of the strut mounts (yes, I opened both sides so that I can compare) using 17 mm socket. Sure enough, the nut on top of the left strut was loose and it took 1/4 - 1/3 turns to tighten it up using 17 mm socket. The nut on the right side was tight and I couldn't tighten it more (and there was no knocking noise on the right side anyway). Mounted the struts back in place and voila! the knocking sound from the left side of the trunk is gone! Thank you so much again!

P.S.: someone asked if the location of the strut mount nut can be accessed from the trunk - the answer is no. Not for 2016 Prius model (gen 4). I used to have 2014 Prius (gen 3) and I remember there were plastic pop-opens to access strut mounts. The same job in 2014 Prius would have been easier as I would save myself the trouble of taking off the wheel etc. and won't make my hands so dirty. But anyways, it is behind me now and I am glad it is FINALLY fixed, and at no cost!!! (except that $25 "inspection" fees by Firestone, bummer!)

P.P.S.: someone asked the torques to use to tighten the strut mount assembly (two screws on the side that connects to the chassi) - I used 40 ft-lb (not an expert advice, just sharing what I used!) This is a guesstimate based on about how much I had to push to loosen those screws (I opened 4, and I must admit one was super loose - I could turn it loose with my hand!) - having said that, as someone else mentioned, shocks are not critical for safety, but are important for smooth ride, so I think the exact torques won't matter as long as the assembly holds up in place and can handle the bumpiness of the roads!

 

Not sure from your description what that is, but torque values might be in the attachment.

 

Thanks to @Mendel Leisk (see the attachment in his response) - the screw marked with yellow arrow (to tighten up the shock on the mount, which would fix the rattle) needs 25 Nm (or 18 ft.lbf) of torque and the two screws on side with red arrows (that holds strut mount to the chassis) needs 55 Nm (or 41 ft.lbf) of torque. I am glad I don't have to open it to tighten it to the specs... phew..