"No, the parking brake only engages the trailing shoes."

donbrew - Thanks for the definitive answer.

Not sure I agree with that. The HHR is the only car I have owned that has rear drum/front disks that has exhibited this problem. And I have owned at least 4 or 5 American cars with this configuration over the years. The pulsating issue on my HHR went away when I switched from ceramic pads to cheap semi metallic. The car also stops better too.

X 2, This is the only one (hhr) that is stubborn on self adjusting.

I am not sure that we are talking about the identical thing. What I am talking about is the rear drum self-adjuster mechanism itself, not it's relationship to the disc warp.

The self adjuster mechanism is the exact same system that has been used on American cars for at least 50 years. There is nothing new. They never really worked on 4 wheel drums, and then when they started front disc brakes it got worse, then when cars lost 1000 pounds and got front wheel drive (shifting the weight to the front) self adjusting drums just aren't. The system on my Mazda Protege is different, instead of self adjusting they are just adjusted all of the time.

If you look at the drum brakes on a 1964 Dodge Dart you will see the exact self adjuster parts.

donbrew-

Both my chevy S-10's had drum rears & they adjusted fine with a short back up & hit the brakes a couple times..

Not so on my hhr..

What I'm trying to get at is that the system on your S-10 is the Identical system on the HHR. The differences are in the curb weight and the weight distribution. Your S-10 has rear wheel drive and a lot more weight on the rear when the weight shift occurs from the back up/braking maneuver.

Did you ever actually hear the click? Or are you assUmeing that the stayed adjusted, on a small pick up the rear brakes just barely keep the rear end from fishtailing while the front disc brakes are doing 97% of the stopping. On the HHR the braking distribution is different, probably something like 80-20, enough that the rear shoes actually wear. I know that my last 3 Toyota pick ups never needed rear shoes after 200,000 miles, but front pads every 25K.

I remember the brake mechanics in 1968 chuckling about self adjusters, and how much money they were making for them. One thing about them is that only the one that is already properly adjusted will "self adjust" the other one will stay loose, in other words the tight one will get tighter and the other one hangs loose. They do not equalize.

Also make a distinction between "pedal pulsation" and "brake shuddering". On my HHR I get "brake shuddering", but it comes mostly from the rear even after totally new rear brakes backing plate out (including bearings), some from the front. But Ceramic Pads help a huge amount I have been converted!

I didn't assUme anything.. I pulled the wheels to clean & paint the drums on both my S-10's.
& checked the adjustment..

If my parking brake had too much travel, I would do the back up/ hit the brakes a couple times or so & the parking brake traveled much less to hold the truck, & in a gravel parking lot, hitting the brakes I could lock all 4 wheels up..

The HHR will not self adjust like this, least not mine & many others..

Our cars definently have this issue. Ehow mentioned our cars have premature brake wear.

"Pedal pulsation" vs "brake shuddering" is just semantics. Everyone describes it a little differently. The only time I have ever experienced rear drums actually shuddering is when they were manually adjusted too tight.

I can tell you that my issues with pulsation/shuddering started at 10k and about every 10k to 12k additional mileage after that. This after having the dealer fix it twice under warranty, and myself replacing the rotors and pads a third time with good quality aftermarket parts. The 4th time I simply replaced the pads with cheap semi-metallic and I haven't had a problem since. That was at about 45k and I now have over 70k on it. And I've never touched the back drums/shoes other than to take them off and inspect them during a normal tire rotation. What I'm saying is that I'm not convinced that the back brakes have anything to do with the front brakes pulsating or shuddering.