Hi folks,	

        Off and on I've noticed a metal rattle sound coming from my passenger side front wheel.  today I pulled off the hub cap and found the small cover that lives in the center over the large nut was off and only held loosely in place by my old style metal bus hub cap. 

        I pushed it back on but it pulls off again easily.  What is supposed to hold this small cap in place?  on the driver's side the cap has a small pin like thing coming out of the center.  Not sure if this is holding it on or if the drivers side is different for some reason. 

so, how can I secure this small cap?  What is it called exactly? and though there was some grease in there I wonder if that should be changed or boosted.

advice and recommendations are greatly appreciated. 

Eric Caron 
85 GL Auto