Originally Posted by dgregory57
Just in case... A different bike, but same symptom for me.
No matter how much I tightened the QR it wouldn't hold, same problem after switching to a binder bolt.
I then got some advice to line up the slot in the shim with the slot for the seat post... and it hasn't slid since. I didn't even realize I had a shim... but it came that way from the factory, and it seems that I twisted it when I was fiddling with the seat post at some point.
I had a Giant that came from the factory with a shim, and like you, I didn't realize it was even there for a long time. I never could understand why Giant used a shim instead of stocking it with a properly sized post.
In this case though, I know for sure that there is no shim. Thanks for the suggestion.