Just put new brakes, machined rotors on 2007 LT. Did not correct issue. is the a suspension component thats bad? Only present when braking at speed, not around town.

 

Have a close look a the LCA rear bushings, they can cause a lot of brake shake!
The one on the left is my old 2 piece bushing, it's supposed to by one piece like the Moog Peoblem solver bushing/bearing on the left, part number K200792
They don't list the HHR but it fits the LS/LT FE1 and FE3 suspension
http://www.moogproblemsolver.com/moo...ings_Sheet.pdf

 

Also I have seen the rear brake drums out of round cause brake pulsation at high speeds.

 

I have a somewhat similar and intermittent issue, with all new factory rotors, pads, new tires, alignment and balance. Is the shudder on yours with pedal, steering wheel, or body?

 

Personally I would take the rear brakes apart and make sure the self adjusters are working correctly.

Replace all the hardware if need be.

That was my main problem on my '06. Having the rear brakes set properly will cure a lot of front end wobble problems.

 

Trex08 , has a point but the front end alignment only allows for toe adjustment.
The rear drums can be an issue for brake judder but at all speeds.

 

Like oldblue said, I would check the the lower control arm bushings. When mine went south it could be felt at speed but not as much round town. I think we have all had the rear brake adjustment issue as well as the warped front rotors but for me it was a different feel than the bad bushings.

 

I agree with VinceP, after putting 227,000KMs on my 2007 HHR, I have replaced front wheel bearings, both lower control arms, numerous rotors and pads, rear springs, and rear brake rotors and shoes. Take the advise of adjusting the rear brakes it makes a world of difference, the front rotors are not always the culprit.