Play in Cleat/Pedal When Clipped In - SP
 

I'm using Shimano CT45 shoes with SH51 unidirectional cleats as pictured.

The right side shoe/pedal seems to have play when clipped in, as if the retention mechanism is not holding the shoe all the way down on the pedal. When standing under power, sprinting or powering up a hill and pulling up on the pedals I can feel the shoe move up and down in relation to the pedal surface. I can clip in the right shoe and reproduce the problem while standing still - pull up and down on the pedal and hear a definite click-click with some play between the cleat and retention mechanism.

This happens with two different sets of pedals, the M530 pictured and PD-8000 CX pedals, right pedal only, either side of the pedal. I've changed the cleat on the right shoe and adjusted retention spring tension on the pedal with no improvement. Cleat retention bolts use Loctite.

http://3.bp.blogspot.com/-HCAZoaNMvP...600/pedals.jpg

The only logical explanation I can construct is that the right cleat is seated at a shallower position than the left, so you would either have to make the surface deeper or the cleat thinner to resolve the problem.

Try it with a different pair of shoes.

Shoe soles being a "plastic" which has been molded are well known for not being exactly perfectly formed. Some warping or other minimal shape change from the mold is very common. Andy.

Had the same problem and found out that standing full weight on the pedal after clicking in resolved the clicking/play. And over time doing this the shoe has 'broken' in and let the cleat seat better. I actually would stand and put full weight on the pedal and then rotate my foot left and right.

Exactly. We find at work that the lower cost "recreational" SPD shoes with more rubber like soles have more issues with complete cleat engagement then the higher end and more plastic/carbon soled ones do. We often do a little sole surface grinding away or trimming to allow better clean/pedal fit. Some pedals need more then others do. Andy.

Agree, Andrew nailed it. It is all about the pocket depth in the shoe and the material the sole is made of.
I have an old pair of shoes with black soft rubber and a shallow pocket and they engage like butter but squeak and have vertical play as you describe. They also float real easy.
My race shoes have a deeper pocket and harder plastic soles and i have to apply some pressure to engage but they have zero vertical play and tighter float as expected.
I have other shoes that i ground the sole for a perfect fit.
Shim cleats or grind sole as needed to get the fit you want.