I glued pads onto my BMW tank last year, using 3M Super Weatherstrip Adhesive in black. First though, I watched a couple YouTube videos and found that less is more with this stuff. It is also necessary to remove the mold release agent from the backside of the rubber knee pads.
I laid the pads upside down on the bench and sanded with a random orbital sander till it looked like the rubber was a uniform, flat black, lightly scuffed surface. Then I scrubbed with a brush and some tire cleaner and hot water. I dried it with a hair dryer, but once dry, I could see there was still some whitish mold release agent present in some spots. I repeated the process and this time it looked uniformly ready.
One side at a time, I applied a light bead of adhesive, smeared flat, thin, and clear out to the edges with a flexible plastic putty knife, on both the tank and all over the backside of the pad. I let them set up till I could feel it was only a little tacky (wearing latex gloves because this is deadly stuff)
. Then I made sure the pad was positioned and stuck it on.There is no adjustment, so be sure it is right
Instantly, the pad was adhered and I could tug at the edges all around without any hint of it coming loose. You could use a paper slip sheet with this adhesive, to get the pad into position, but I took my chances without that. My tank has well-defined recessed areas for the pads, so they were easy to align. On a Bonneville tank, I would want to mark the outlines somehow before applying the pads, maybe using a dry-erase marker, or outlining the pad area with painter's tape.
One year later, they are still in place.