The other area of my Grand Prix the has rot issues are the mount points for the rear trailing arms. Here's a decent looking one.....





Here's mine....



In the GM parts guide this part is referred to as the Rear Rail Lower Reinforced....



It's not exactly obvious where this part goes until you start removing parts. It's welded to the rear rail and floor. It covers and reinforces the trailing arm bracket mounting point. This is what it looks like in place. Without the trailing arm mount obviously......





This is what I found underneath mine when I removed it....



The piece with the 3 threaded holes next to the rail is referred to as the Rear Rail Upper Reinforced It is covered by the Rear Rail Lower Reinforced mentioned above. It also includes the thread hole that the rear outer seat belt bolts to. It looks like this....



After some sand blasting, repair work and epoxy primer.....







When I did this repair I didn't realize what the Rear Rail Upper Reinforced was. So I went ahead and blasted the outer and cleaned up the inside as best I could and then primed it. In the GM parts guide pictures it's a pretty small part. I was unsure if it was the part I was looking for. Because the parts counter people aren't always familiar with these intricate parts that probably rarely get replaced they couldn't tell for sure if that's what I needed. The reality was they are really inexpensive so I took a shot and purchased it. Luckily it was the right part. So I'm going to remove mine and replace it with a brand new one. I'm already in there and there's probably only 10-12 spot welds I need to drill out. I would hate to go to all this trouble and just leave that part buried underneath every thing.

The Rear Rail Upper and Lower Reinforced are readily available as they were used on the Chevy Impalas all the way until 2016. Best of all they are super inexpensive. Here are the part numbers...


  • Rear Rail Upper Reinforced(Inner trailing arm mount. Thread holes mount bolts to)
    • Left - 20962316 - $22
    • Right - 20962315 - $22

  • Rear Rail Lower Reinforced(welded to rail and floor pan. Goes over Rear Rail Upper Reinforced)
    • Left - 20962273 - $39
    • Right - 10406995 - $39


Of course the trailing arms and trailing arm mounts are also very inexpensive and readily available from RockAuto.

If you are going to all the trouble and expense like I am I would highly recommend considering having these parts replaced as well. With the inner rockers removed these parts are very exposed and easy to access.