I have owned my 1992 coleman Seneca popup for 3 months now. I have just put my 5th dust cap on and have the 6th one in the TV. Why do they keep coming off??? Here is my theory. Tell me if I am wrong. Metal expands when it heats up. Not having the cap on all the way the hub opens up an loses its grip on the cap and it fell out. Many times. By me putting it on while warm, it went in easier and as it cools it should crimp the cap and lock it in place and never ever fall out. Right? When I bought it I knew it was missing. I went to the auto parts store close to home and bought a Ford dust cap that seemed to fit. It was 1 31/32. I left for the first camping trip and it was gone by the time I got to the campground. I must not have tapped it on hard enough. I bought a 2nd dust cap and banged it on there. I saw it roll off in the middle of the highway. Darn. I do some research online and call an RV store. For a trailer I need a dust cap that is 1.98 inches. The ford 1 31/32 works out to be 1.96 inches. OK, two one hundreths of an inch was the problem. They are cheaper too, $5 for two -vs- $4 for one Ford dust cap. I put 3rd one on. It was a bitch to put on, I had to really bang it. I go to the Spring Gulch Rally. It's gone when I get there. WTF? Now I know this problem is beyond me and I call the RV place to get a quote to repack the bearings and for THEM to put the dust cap on. $150. DW and I talk about it as we are going through the mail and what do we see??? A coupon for Stolfzus RV $99 per axle. I dropped it off last weekend. I picked it up on Thursday night. I checked the 4th dust cap. It is really on there good. This is not going to come off. Of course, by the time I got home it did. I went back this morning and watched as the guy put the 5th one on in the parking lot. I talked with him as he did it. He was really banging it and it was not going on any farther. It was not on down to the little lip. He said it was tapered so that it would get a better bite as it goes in and that was it. OK, makes sense. I leave and I am smart this time. I pull into the first parking lot I can get into. Good timing. It was just about to fall off. Hmmm. The hub was at warm operating temperature. I can basically put it on and off for a little bit, not like I have to bang it on like when I first put it on and it is cold. Is this the issue???????? I bang it on while it is warm. I get it on down to the lip. I check it again. It's still on good. I check it another time. It's still there when I get to my destination finally Will it fall of again?