Ok so I just had this happen as I was changing out my rear shocks the other day. I'm writing up my experience because there was only minimal info I could find in the HHR/Cobalt world and, as with my luck, I had further issues that weren't covered in the other posts and I wanted to leave this note for anyone else that might have the same problem as me.

Long story short: the rear bottom bolt is at a liiiiitle bit of an angle and if you run it in with a power tool there's a chance you might not have it seated right which will lead to it getting stripped. I found this out when the PS went in fine but the DS wouldn't torque down and would just spin. Googled the issue and found a few people on Cobalt forums that had the exact same problem and they all claimed it was a GM issue/easy to mis-thread. Made me feel a tiny bit better anyway. Their solution was to just tap out the axle, fix the bolt threads, and viola they were back on the road. Try this first and hope that it works for you.

But oh, if only it was ever that easy for me when working on cars. I ordered a new bolt from Ebay (GM# 11518185) for about $16 but later found the correct size at BOLT DEPOT (stock size is M14x2x75, grade 10.9) which would have been about half price. Also picked up an M14x2 tap/die and waited til they came in the mail. I tapped the axle first, ran it right in with no problems, but when I put the new bolt in I found that it was just a little wobbly. Thinking maybe it would be tight once the shock was on, I reinstalled it only to find that the bolt was still loose. *****. Upon looking back I think the whole issue was due to using power tools, coupled with the slight angle the bolt needed to go in. Since I used my 20v impact I couldn't get right up to the hole due to the drum/hub being in the way, and by the time I'd added several 3/8 extensions my angle going in was off. To avoid this going forward I removed the whole hub.

At this point I figured the only way to fix the issue was to tap the axle larger and get a bigger bolt so I ordered an M16x2 tap and a few bolts from Bolt Depot (just to have extra and to see what the best fit was) and waited a few days. When they arrived I realized an M16 wouldn't fit through the sleeve in the bushing which meant I had to go to Home Depot and get a drill bit (M16 is approx .6299", just over 5/8" which is the largest bit HD had). Unfortunately, despite my best effort, I couldn't get the sleeve drilled out. Frustrated, I said F it and brought the strut and bolt to a local machine shop. They said sure, no problem, we can get it drilled out for you, just come back tomorrow. Well the next day I get a call that they can't drill it out either. Obviously the sleeve started to spin in the bushing and then the bushing tore. At this point I wasn't sure what to do, so I went to several parts stores and found the closest off the shelf bushing to fit the bottom of the shock, drilled out the inside of the bushing, made my own metal sleeve from pipe, and got the bolt/shock portion to where I needed it. All that was left was drilling and tapping the axle, so I set to work with the 5/8" bit. It got through the axle part fine, but there is a threaded nut welded to the inside of the back that wouldn't budge even with a hammer drill. Of course that nut is inaccessible without cutting the axle itself. My god, what had I gotten myself into?

Now the only options I could see were to buy a new/used axle assembly and swap the whole damn thing out, or to try and weld a nut on the outside. My first choice was to swap, but there are no U-Pull junkyards around here and since it's been 9 years since they made our cars I wasn't having any luck finding a local car being parted out (even Cobalts/G5s). I'd been trying to do everything right at this point, but by the time I had to fabricate my own bottom bushing I'd kinda given up. I ordered four different types of nuts from Bolt Depot, waited another few days for them to come in, borrowed a MIG welder, and set to it. I threaded a 10.9 steel nut all the way up the bolt until the threads ended, stuck it in the axle, readjusted the nut so it sat flush with the angle the bolt needed to be at once the shock was on, and spot welded it to keep it in place. I then took the bolt out and welded the nut the whole way around, cleaned up/grinded down the welds, and went around it again. Next I sanded it down and sprayed some X-O Rust, then reinstalled the hub.

Finally the moment of truth: I reinstalled the shock and--praise the Lord--it torqued down to specs! I bled the brakes since I'd disconnected when I'd taken the hub off and put it all back together. I drove it around the block a few times and there was no clunking sound like when the bolt had been loose so I think it's fixed for now. I plan to swap out to an HHR/Cobalt SS rear at some point just for the sake of not trusting my life on a welded nut, plus it's the perfect excuse to get me some rear discs.

Overall, this was waaaay too much work for a car with only 67K.

Anyway, I hope no one has to go through this whole mess with their car and if they do I hope just retapping the M14 will work (advice: remove the hub before trying) but if that doesn't work you might want to skip trying to tap it larger unless you are positive you've got the tools that will get through the nut on the back. If not, you'll have to weld a nut on the outside so the bolt will have something to thread into. Good luck future you!

 

Thanks for the write up and sharing your experiences of correcting the problem!
Rule #1 thread the bolt in by hand after you slathered it in anti seize!
Rule #2 no impact power tools !
Rule #3 refer to rule #1.