Wish me luck with this 2006 LTZ. I can't get it down the road. This is worst than the last one. First I had to buy a new throttle body, then I put new brakes and rotors all around, then had to fix an oil pan leak, and while doing that I threw a reman tranny in, and two new axles. This one may top the 05 very soon. Now the dealer cannot find out what is wrong with the brakes. Very soft pedal, and it goes to the floor. Put a new master cylinder on, and the tech took it for a ride, and flushed the whole system. When I picked it up, the pedal was even worse and went to the floor immediately. He said it did not do that when he drove it. Now they are talking a brake booster, which is not available OEM, but according to Cardone, those are not the symptoms for a bad booster. I have driven this car about 300 miles. Oh yeah, the pan gasket failed, so had to fix that, but they are reimbursing me somewhat - a whopping $50 an hour labor. I asked if this was 1985. I think I have had enough Monte Carlos.

That's very rough! I feel your pain though on the brake system side, my 2 piece rotors average 350-375 or so each! Not pretty when i had to replace all 4. And decided to replace all calipers at the same time another 375 each! Unless you absolutely love these cars or have sentimental value for one, it's certainly hard to justify the repairs compared to the value.
Now not being able to figure an issue out is most frustrating and leaves you with a feeling of dejection. There were instances where I didn't even want to look at my Monte, but once I calmed down, I was able to troubleshoot with a cooler head.
Of course this certainly doesn't help you but hang in there. If you truly do not care to go through the trouble, dump them both. Very strange the dealer couldn't figure it out though.
I wonder if a line is leaking somehow.

So a very silly topic comes to my mind. Commonly this item happens when people have both calipers off the car at the same time..... If anyone removed/changed the calipers, make sure the bleed screw as in the top most position, if it is pointing down, someone mixed up the calipers, therefore is not properly bleeding them, there will be air in them and thus a soft pedal. Sometimes when using factory parts on different cars that they were not made for (like doing the F-body caliper upgrade on a W-Body car). The calipers may have a L or R for Left/Right, but that refers to the car they were designed for, not the car you are trying to put them into, thus there position on the spindle may differ and that means left is now right and right is now left.
Anycase, like I mentioned, if the calipers have been off the car, just double check the position of the bleed screw. I have seen some of the most seasoned and experienced mechanics blindly over look that one.

Well here is an update. I bought a Delco MC from Amazon, around $58. Good price. It wasn't until this happened that I got back home and started digging. GM does not even make the MC anymore, but I did get the GM part number and used it for reference. There are two for these cars. One non-ABS, and one ABS. I didn't even think they made cars without ABS anymore, but guess so. Anyway, on Amazon it came up EXACT FIT, so like an idiot I trusted them. None of the local parts stores had any, or they wanted more than double what I paid. So anyway, I have RPO JL9, which is 4 wheel independent ABS, and Doorman makes one for $59. M630439. Now get this.....Amazon had it all along, and it never came up as an alternate. Now, this is just step 1, which I dearly hope fixes the car. The booster is good, but they tried to explain there is one other part that is so expensive I don't even want to know how much, but it distributes and contributes to the ABS working. BTW, the factory part number for a 2006-7 LTZ is 10209185. This does NOT fit the SS.

Now about your other mention. I had a guy do some work on the car, and for some reason the rear brakes started hanging. I could smell them when I got home. Took it to the dealer and they finally said it needed new rear hoses, because the calipers were free. So I paid to have them changed out. I got halfway home and started down a hill and the car lost speed. I was livid. Took it back to the dealer and they smoked it over again and it turned out to be the calipers. Can't even tell you why, but I know when I did full brakes on my 05 MC, I also used Delco reman calipers, and that car not only has a very tight pedal, but stops on a dime. So take this info for what it is worth. I will update Tuesday or so when I get the right master cylinder to them.

Read my other reply, but on my 05 did essentially the same. But I did not spend near what you did. I used a Detroit Axle package that has ceramic pads, and drilled and slotted rotors. I too replaced my calipers, and as I said in the other post, car will stop on a dime. Package was $175 on Amazon, and the Calipers were around $65 each.
https://cimg0.ibsrv.net/gimg/monteca...21817f86f2.jpg
Delco calipers, Detroit Axle drilled and slotted rotors, ceramic pads.

I certainly hope you get it figured out sir. The part number deal, and all that, is annoying. There are parts on my 2022 that Amazon says doesn't match but I know for a fact they do. With the Monte I try to order from Rockauto whenever possible but parts are certainly becoming harder and harder to come by. Good luck and hope it's corrected without much more headache.

After this I will look up the OEM Part if I can to confirm. GM has turned Asian, and just wants you to buy a newer car. They are not going to help you keep yours on the road. Sadly, they should realize they do not make a coupe worth having, so these cars are the only alternative. I just went to advanced and bought two reman calipers. Only thing I have not replaced on the brake system. and have already done the rears Just hope that expensive part they mentioned is OK. Going to give it every chance to act right first. I have used Rock Auto and Parts Geek. I like them. On most parts it even says exactly what it will fit. They even had a different starter for my Supercharged car. I am going to have about $8K in this car when it's over, and everything will be fresh but the motor. It seems to run great. Thanks for the encouragement.

To following up, has this moved yet?

No idea. I have lost interest. Now the tranny is leaking again. What a nightmare this has been. I am in a small town now, and even though it is at a Chevy store, the work is less than impressive. I am ready to be out of the MC business.
https://cimg0.ibsrv.net/gimg/monteca...28b5571cd8.jpg
The Exxon Valdez.

Very sorry to hear this. Where is the trans leaking from?