well, like I said, I don't have one to look at... but if I remember correctly there should be a groove on the shaft that the snap ring goes on. Just make sure that's lining up correctly... you maybe putting it down too far. Other than that I'm afraid I might not be of much help since I don't have one.

 

I replaced the plate and **** on my '78 a few months ago, its pretty much the same. Pop the button off, remove the snap ring with pliers, pull the **** and plate off, put the new plate on, put the **** back on, align the snap ring on the shaft in the middle of the **** and push it into the groove onshaft(I used two flat head screw drivers to spread it open and push it down into the groove, you dont have alot of space to work with) Then just snap the button back into place.