While I am not sure about the Newmar, I know that on many other brands, you can jack up the slide out about an inch, or so, to get enough room under it to get at the bolts on the bracket to replace the roller. It is a bit tight. But it can be done. Before you start it is best to measure how much clearance you have over the top of the slide to the top of the opening in the wall. That dimension is how much clearance you will have to work with.
Best to extend (or open) the slide only about half way. That keeps the balance point of the slide in the right position, so that you can lift it off the rollers. And of course, you need some pretty good jacking equipment, because the bottom of the slide is high off the ground. Be sure to spread the load at the jacking point, so the jack doesn't poke thru the floor. Although you only need to lift it an inch or so. Once you get it jacked up, put something between the slide out and the floor, so it will not fall of the jack and injure you while you work. If you have access t a fork lift truck, that is the best way to lift it to work under it.
Here is another idea for you. Get a couple of 2X6's (or 4X4's) and cut them to the correct length to wedge them under the slide out. Make sure the trailer will not move. (Hitch it to the truck with the parking brake on.) Then let the air out of the trailer tires on the side where the 2X6's are. The trailer will settle down, but the slide will not move. That gives you the clearance to work under it. I have seen it done this way. When done re-fill the tires and remove the 2X6's. But use caution. This method works good because it is easier to control the clearance you need. But just do NOT instantly remove all the air out of the tires. That could force the top of your slide into the upper part of the opening. You DON'T want that to happen. Damage will occur.
But like I say, not sure the Newmar will work using these methods.
'12 F350 SB, CC, SRW, 6.7 PSD, 3.55 RAR, 6 spd auto
2015 DRV 38RSS 'Traditions'
Pullrite Super Glide 18K
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