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2007 Cobalt Subframe Replacement 

My Cobalt drives well except that it really sways at high speeds and has about a 15 degree tilt on the steering. Its a rebuilt car that wasn't rebuilt properly and I determined that the subframe would need replacement. Replacing a subframe is doable at home but given the nature of the damage involved in my car; There was a possibility that I would have had to pull the chassis frame using a frame machine to line up the replacement subframe with the mounting holes on the chassis. For that reason, I rented a hoist at my former work place just in case I needed to send it off to the body shop next door.

April 2015

Here is my daily beater 07 Chevy Cobalt LT.

Prior to my ownership of this vehicle, this car was involved in a major driver side collision. It was rebuilt but the a decently sized notch was still on the subframe and it threw off the alignment pretty bad. The driver side wheel was also displaced way too close to the wheel well causing contact when the brakes are slammed.

I took a look at the engine bay and realized that the engine has two side mounts that are mounted on the chassis rails. This meant that I would not need the engine to be hanged to prevent it from falling on my head as I remove the subframe.

First thing first, wheels off. Four 19 mm lug nuts.

The subframe's interface with the struts would have to be removed. Decided to release the sway bar links from the strut (which wasn't the best idea as you will see later). Had the exposed threads soaked in WD-40 and ram open with an impact gun. 18 mm GM nut here.

That did not work. Used a vise grip to prevent the connection from spinning in order to allow me to ram the nut off.

Release the two ball joints.

17 mm bolt and a 15 mm nut on the other side.

Hammered a fork into the ball joint interface.

until broken loose from the spindle.

As such. This ball joint won't simply slide out. It is a tight fit and would require to be fully released prior to subframe drop.

Next, removed the steering rack from the subframe.

Hand Ratchet was ideal on the driver side.

Two long 18 mm bolts here. Won't be able to pull the driver side bolt out (not much space) so loose it off and let it float.

Passenger side has much more room. Can actually use an air ratchet here.

Now for the rear engine mount located in the rear center of the subframe just below the Cat converter.

Would need an 18 mm socket with a 2ft extension.

Run the tool through the passenger side.

And take it off as such.

For the front engine mount, I guess you could either use an 18 mm wrench or an 18 mm socket attached to a flex end with a 1.25 ft extension on an impact gun. I opted for the latter.

Capture the bolt..

And ram it off through the driver side corner.

18 mm front mount bolt.

18 mm rear mount bolt with some sort of a plate. It seems to have been designed to prevent excessive play/dispacement in the rubber mount. A counter measure for a poorly designed mount perhaps?

Got to take off the skirts around the front two corners to get access to the front two subframe mount bolts. 7 mm screw here (removed).

Two plastic push in clips at the bottom.

A 7 mm screw right above it.

Another push pin clip behind the brake line.

And another 7 mm screw closest to the oil pan.

21 mm bolts here connecting the subframe to the chassis. 4 in total with one in each corner.

Tool setup. 21 mm socket on a 6 inch extension.

First, take off two bolts corner to corner diagonally.

Then placed a beam along that diagonal.

Then I removed the other two bolts.You might need to pry the front and rear mounts loose and then lower the subframe. Apologies for not taking a picture of the underside with the subframe removed. Would have been informative indeed.

Old subframe on the left. "New" subframe to the right. Need to transfer the control arms from the left to the right. Notice the replacement subframe did not come with sway bar links. I should have disconnected the sway bar links on the sway bar and no the strut. Just a bit more work now that could have been avoided.

Two 15 mm bolts on each control arm. My replacement subframe came with the sway bar so I did not have to transfer that.

Make sure you have a good feel when putting the bolts back on for the control arm. GM bolts aren't that tough and the ones between 10 mm to 15 mm do tend to rip easily.

Here is one of the four subframe mounting bolts. It is imperative to clean off rust and corrosion off such bolts. Rust on bolts disallows applied torque to be translated into thread engagement due to jamming (which in turn causes bolt heads to rip off) and makes it ideal for the threads to mis-match causing them to strip. Used a wire brush here to remove plenty of rust. Brushing the bolts removes the anti-corrosion coating but that coating is of little use once the bolt has rusted to this extent.

And the bolts were subsequently soaked in plenty of WD-40.

Now here is a part of the culprit. Notice how the sheet metal for the subframe mount on the right hand side is angled as a result of the collision.

Compare it to the passenger side (No collision). Its flat.

I jacked up the replacement subframe and lined up the subframe with the bolts. Just turned the bolts enough to catch the threads. You would want to leave plenty of wobble so you can work on lining up the holes effected by the collision like in the picture here. After plenty of prying and displacement using hydraulic tools; the bolts did line up.

Once all four mounting bolts have been lined up; I used the jack to sandwich the subframe to the chassis and the tightened the bolts.

Make sure to line up the radiator mounts prior to tight-up. They are plastic and will break your radiator if you forget.

Then I sandwiched each corner of the subframe as I torqued the bolts. If you don't sandwich the subframe to the chassis, you run the risk of stripping the threads on the bolts due to the possibility of the subframe bearing some of the weight of the engine. Though the bolts are quite large and the chances of that happening are minimal; Ideally you don't want to load a bolt and torque it at the same time.

Tried lining up the front engine mount. I couldn't.

Screw up #1. I did not consider lining up the engine mounts while lining up the subframe. The bracket on the engine ended up sitting on the rubber dampener's aluminum through hole. Hitting the side of the through hole with the a prybar and a hammer popped it into the bracket.

Bolt put into the through hole.

And torqued. Front mount was bolted on and torqued after. You may have to jack the pack and wiggle it around so that you can match the holes and threads.

Steering rack bolted back on.

Ball joint bolts back on...kinda...

Rammed it in causing screw-up no.2

I did not line up the cutout on the ball joint with the through hole properly causing the bolt to strip when I rammed it. Since it was a nut-bolt connection, I was able to get away easy with a replacement bolt. If internal threads were involved, I would have been screwed.

Decided to put on new sway bar links instead of using the old ones still on the old sway bar. Might as well since as you have seen earlier, taking them off isn't much fun because the studs spin with the lock nuts. Plus they are only 17 bucks each (after market).

Wheels back on and good to go..Though I did get more clearance around the wheel well; it wasn't to the desired level. I might replace the control arm if I happen to find one at my local scrap yard.To be added to this page if so...