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Demco Premier Series 5th Wheel Trailer Hitch Above-Bed Base Rails Installation - 2017 GMC Sierra 250

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How to Install the Demco Premier Series 5th Wheel Trailer Hitch Above-Bed Base Rails on a 2017 GMC


Hey everybody. Ryan here at etrailer. Today on our 2017 GMC Sierra 2500, we're gonna be showing you how to install the Demco universal in-bed fifth-wheel rails. But before we do that, why don't we check them out and make sure that these are gonna work for you. So with this being just the rail kit, so you're gotta get your rear and front rail, and of course, some hardware to help you get them installed. And it kinda had me thinking, Why would someone need just the rails And what we kinda came up with, it seems like what a lot of people run in to is they already have a, rails in their truck, and they have a older type fifth wheel head or fifth wheel hitch, and they wanna upgrade.

They wanna kinda get a newer style hitch, and get the hitch only to realize that newer style hitch doesn't fit the older type rails, and that's kinda seems to be the most popular thing that people run into. And so, as opposed to having to get a whole entire new installation kit, you can just swap the rails out, and that's what a lot of people are doing. So these are gonna be for the newer style of hitches. So you're able to remove your old ones, pop these new ones in, and be able to use that newer style hitch. With these being pretty universal, I understand there's a lot of different hitches out there and these will work with a lot of them, but just to kinda double check and give you a little extra confidence, we can grab a couple of measurements here.

And what we're gonna start with is where the hitch is actually gonna drop into the rails, as attachment points. So we'll start with the furthest ones outside and work our way in. So I'm gonna measure from the center. Center to center. That makes sense here.

So there, there. Looks like we're gonna be right at about 29 inches. Then we can go from the ones next on the inside here, center to center as well, and from there, looks like it's gonna be, we'll say 20 and 5/8 of an inch, roughly. And then these real small ones, these inside ones, these are gonna be about 10 inches, I'd say. So you can take whatever head or headshot you have and measure those attachment points, and that'll figure that out and I guess while we're at it, we'll just measure the diameter of those attachment points.

Just do it like this. So it looks like that's gotta be about an inch and 5/8" across and it's like about, just under 5/8" wide, this way in diameter. As far as the attachment points go, so these are gonna be the openings here where you drop your bolts through to actually attach it to your side plates, just to give you guys an idea here, I'll measure from the end of it and work our way in. So from the very end to the center of the first attachment point, it's about an inch to the second one, I just kinda have to roughly, give a educated guess here, 'cause we have a bolt in there, I'd say about two and a half inches. That one is right at four inches. And this one closest to the inside is gotta be right at five inches. Keep in mind with these just being the rails, you are gonna need the side plates to, get everything bolted together and completely installed. If you already have the side plates great, if not, you can always grab these separately or there chances are pretty good too. I know for a fact on our GMC here today, there's a kit that you can can pick up that comes with the side plates, the rails and everything else, but that generally holds true for just about any other make and model of pickup truck as well. So, you have a few different options there and whatever you're trying to do, I'm sure there's a way to best suit your needs. As far as the installation goes with the rails, really not too complicated. The most important thing to do with these is to measure a couple of times, make sure that everything is square and true and when you have something accurate to go off of, everything should just kind of fall right into place. But that said, you're not gonna be installing the rails and not messing with the side plates at all. So we'll go ahead and just walk you through how to do the whole thing, the side plates and the rails, and hopefully that'll help you out. If you don't need to see that part, you can always scroll through it and find what you're looking for, but that said, I will say probably the most difficult part about the installation is actually, believe it or not, torquing down some of the bolts that are underneath the bed. They're just in a really tight spot. And they take a little bit time to actually get cranked all the way down and because they're tight, you can't get kind of your standard socket in there, but I'll give you a few different options on different types of tools that you can use to kind of speed that process up and make it a little bit easier on you. So hopefully that'll help you out and with all that said, why don't we go ahead, pull into the garage and put everything on together now. To begin your installation, you're gonna be here up in the bed of the truck and first thing you wanna do is clean out your bed and make it all easy to work in here. If you have a drop-in bed liner, I suggest removing that, That'll give us the most accurate installation and make it much easier. With that said, the first thing that you wanna do is take one of your rails and we're gotta have to find the placement of it. So you're going to measure, from the end of the bed, make sure you're going from end of the bed and not the tailgate. And you're gotta take that measurement and make a mark and then you wanna refer to the instructions for that correct measurement, because there is a difference between the short bed. Or, I'm sorry, the six and a half foot bed and the long bed. In our case, we have the shorter bed today. But what I do is make a mark and then I just use this as a straight edge to kind of draw a line all the way across and, gotta get it roughly in position and then you wanna make sure that it is centered on the truck bed. So the way I do that is measure from our wheel well to the edge of the rail on each side, and you want that distance to be the same. So once I find that distance, I also use a straight edge and just make a mark there. That way we have kind of a reference and we can make sure our rail is gonna be exactly where it needs to go. So since that line that we drew, the distance, they want you to, line that up with the center of our rail here and so you can kind of look down through the openings and get it pretty close, just eyeball it. But we want to go step further and make sure it's exact and make sure that this is perfectly square. So what I've done is take your measure, go from the end of the bed again, and just go to one edge of the rail. In our case, I just followed this one, so for example, on ours here today, the edge here is about 32 inches. And so I made sure that the other side was at 32 inches and now we know it's exactly square. And once I found that, I just took our marker and kind of traced all the way around it. That way we have a diagram more or less on where this needs to go exactly. Now at this point, definitely need a couple of friends you gotta take your pre-assembled hitch, set the second rail up front, roughly in position. Then we gonna take this and actually drop it into, our rails. And If they move around a little bit, not a huge deal. That's why we marked that one, exactly where it needs to go. So, we can slide it around a little bit if need be. So once you have this in here, what you gotta do, make sure this front rail is squared up and everything and plum. What I've done is made sure the back was where we originally had it and then measure the distance between this edge and this edge and make sure that they're the same on each side. Not a bad idea to check the distance from your rear wheels, as well here. Once I found that perfect spot, again I just drew a pattern around our front rail too, just to give us a reference, make sure that we can kind of constantly keep an eye on it while we're going through this process. From there, each one of the rails, this hole, the second one in, that's the attachment points that we're gonna be using. So, I'm just gonna take a marker, put a dot in the center, I already did the other three attachment points. And then what we're gotta do is I'm gonna drill a pilot hole, just got a small, relatively small drill bit and before we started doing this too, check underneath your truck, make sure you don't have anything that we're gotta drill into. You shouldn't, but if you have any aftermarket stuff down there, whatever needs to be on the safe side. So you're best here to get it in the center. Then we'll drill a small hole on each corner Now we need to do is enlarge those holes that we drilled to 5/8 diameter. Problem is, even if you had that large of a railer type drill bit. it's almost too big to go through this hole and I really don't want to, damage our square opening here in our rail. So since we have each hole kind of pre-drilled and marked already. What I think I'm gonna do is kind of just move our hitch out of the way a little bit. This one looks like I was a little bit off that's okay though. And if you move that out of the way, since we have everything marked already, we can use a step bit like this, or you can use your regular bit, whatever you're trying to do. So with that said, I'll go ahead and enlarge all of our holes. Since this one, I am off just a hair, I'll just try to shift it over a little bit, if I can. So what I've done is vacuumed up all the metal shavings and the holes that we drilled, I shot some spray paint over them. Let them dry just to get a coat of paint over that bare metal. Slide the hitch back into the rough position then you're gonna take these spacer blocks here. Slide that in between the corrugation and the rail. Then you're gonna take, these hockey puck looking bushings, slide them in and line them up with the hole that we drilled, like so, and then we're gotta take the long, I believe they're three and a half inch carriage bolts, drop them down. We're gotta do that same thing on the three remaining corners. Now we can come over to our wheel wells and we're gonna be working on our frame rail. Wipe this down, get it clean, and we're gonna be using four attachment points to bolt up our side plates. It's got two well nuts here and two more well nuts here. Not a bad idea, if you spray 'em down with, some penetrating oil, some type of cleaner and work those threads clean. I'm just using a tooth brush that way you get some of that undercoating out of there. These GM trucks, they really pack on this undercoating and, any dirt, we'll get junk out of there and what we're gonna do, is take our side plate, they are labeled. So you really can't mixed that up. Driver's side these slots up here, our bolts that we put in through the bed, those are gonna go through there and, kind line it all up, hold it in place. We're gonna take a bolt, split lock washer and get these started hand tight. What I like to do is just get one or two of 'em going, that way, it'll kind of hold it roughly into position and a lot of times what you're gonna need to do, every truck will be set up a little bit, a little bit different and how you drilled, vary a little bit. So, you may have to kind of manipulate this plate here to get the bolts to line up perfectly. It looks like I might have to, a little bit here. So what I'm gonna do is grab a tool, so I'm gonna use a tool like this, Just kinda spreads out a little bit. You can see right there, one of those holes is kinda blocked a little bit. I'm just gonna take this, put it up through one of access holes and kinda, work that side plate over, to hold it in position, where I need it to be. Then of course, once we have all of it starred we tighten it down and we'll kind of draw everything together. If that makes sense. So once we have these hand tight, we'll go ahead, go over to the other side and repeat the same process. Now we've come back to the 15th, 16th socket and snug everything down. Now we need to make sure and come back with a torque wrench, tighten down all of our bolts, the amount specified in the instructions. You don't have a torque wrench, you can grab one here at etrailer, or a lot of times you go to your local auto parts stores. We'll have one they're available to rent. So back up in the bed here, I went underneath our truck and just kind of took a look at where we're gonna need to secure these actual bolts and upon further inspection, it seems to me we'd be better off taking these spacers that we had in here originally, and actually putting 'em underneath the truck on this part of the corrugation. That's kind of a. One of those deals 'cause our bolt is literally going through, the edge of our corrugation, So it could go really either way. If you put it here, this one it crush, we put it here, one it crush. But I think what our best option is, to pull these out since we don't have any bolted down, you can just knock these out. We're gotta put these underneath and you're also gotta have these large ones. I think you're gotta put these here under there and that way, if it does start to crush a little bit, this is gonna stop it and prevent that from happening. If it doesn't not a big deal, we can always just slide these back out whenever we have everything tightened down. So I'm gonna go ahead and switch all these out and then go underneath the truck. So underneath our truck, you can see here, our frame brackets and where our bolt comes down, then get a spacer, slide this through. Like so. Now all these, they might not go in that easy, you might have to kind of pry up on your bolt, slide the block in, drop the bolt back down, or kind of pry this down a little bit. Every truck is just gotta be a little bit different. But once that's in, we're gotta take a flat washer, put that on up and a flange nut, get this going hand tight here, and then repeat the same process for our three remaining corners there. So now that we have all the bolts in there in hand tight, I came back with a regular box wrench and tighten them down as much as I could, which brings you to my next point, Now it's time to torque them down and you don't have a ton of space up there, so you can't get your classic socket on there. There's a few tools that you can use to make this a little bit easier, and they're all gonna be 15, 16th in size. One of them is like this, I believe this is called a dog bone, if I'm not mistaken, this one worked out pretty well, It's relatively thin. The other one, you could use a crow's foot, like this and all these just go on the end of the torque wrench, like that. So it's kinda low profile and then there's another one, I assume this would be a crow's foot as well. It just doesn't have the extra sides like a line wrench or something would. Unfortunately I don't have the right size in this one, but tightening a couple of bolts down already, one like this would probably work the best. So it's a lot more low-profile and a little bit easier to get in there. But with that said, we can still make do here and now that we know what tools you can use to get this process done, let's go ahead, We gotta grab this one and I'll show you one of them getting torqued and how this works. So the way this works, it'll slide in there and go up and around the bolt. Obviously before you torque everything, you wanna get them as tight as you can with, with the regular box wrench, try to draw everything down evenly, but once we have that gone, We'll come back and make sure it's all torqued. If you could see it, there's just not a ton of room up here. So it's gonna take a little bit of time, be patient with it and take a break in between if you need to, it can get a little frustrating. With everything torqued down. What I did was remove our actual fifth wheel head and in our case, we had this bedliner. So I dropped that in, kinda eyeballed it. Kinda measured out where it's gonna hit our rails and I'm gonna just cut an opening out here. I lay it in there, make sure it fits and then I'll do the same thing for the rail up towards the front. So I'm just gonna use an aerosol to do this, you can use a cutoff wheel, kind of just whatever you have laying around. So I go ahead and get that done now. Oh, got that cut out and dropped it on in and it's in there loosely, but it looks good. Pretty happy with it. So what I'm gonna to do is just measure the distance between our back rail to the front one, take some rough measurements and then I'll probably just use a piece I'd be cut out here. Kind of as a template saying just roughly measured stuff is down. Make her lines and come back, get your cut. And that'll finish up our look at and installation of the Demco universal and bed fifth wheel rails on our 2017 GMC Sierra 2,500..


Info for this part was:

Employee Jeff D
Installed by:
Jeff D
Employee Joshua S
Video by:
Joshua S
Employee Jacob T
Video Edited:
Jacob T
Employee Ryan G
Test Fit:
Ryan G

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