Bed to Cab gap question

[Conundrum]

I am hopefully going to be shortening my frame soon for the short bed conversion on my 74 GMC.

And I was wondering if I could get the amount of gap on some of your trucks between the front of the bed and the rear of the cab?

I would like to close up the gap some and figure if I can get a few measurements then maybe I could come up with an average that I could add to the 14" that comes out of the middle of the frame already. I figure on coming up with an average, because i'm sure that not all trucks are exactly the same.

[Conundrum]

I don't think it would matter if the measurements come from a lwb, swb, 2wd or 4wd.

Guess I could just shorten the frame down, put the bed where I want it then get the rearend centered afterwards.

[54Caddy]

I seen at truck here in my town at dangerzone truck show. And instead of leaving the gap when he shorted his he made it like a unibody looked nice man. For an idea but that will be a high stress point.

[Conundrum]

That would probably be pretty cool, and alot of work to make it so you don't get any stress cracks.

I would like to close the gap by half of what the gap usually is or so, but i'm trying to figure out just how much that is.


Anyone want to measure the gap between the rear of the cab and front of the bed for me?

[68 TT]

Originally Posted by Conundrum

That would probably be pretty cool, and alot of work to make it so you don't get any stress cracks.

I would like to close the gap by half of what the gap usually is or so, but i'm trying to figure out just how much that is.


Anyone want to measure the gap between the rear of the cab and front of the bed for me?

My 78 is right at an inch.

[b454rat]

If you cut the frame BEHIND the front bed mounts, the gap won't change. But I think it's an inch or so like 68 TT said.

[Conundrum]

Originally Posted by b454rat

If you cut the frame BEHIND the front bed mounts, the gap won't change. But I think it's an inch or so like 68 TT said.

I figured I would add in the amount that I want to close up the gap to the 14" that has to be taken out of the center of the frame anyway, pulling the bed and rearend forward to close the gap a bit and keep the rearend centered in the wheel wells.

[Conundrum]

Originally Posted by 68 TT

My 78 is right at an inch.

Thanks

[bluex]

When I shortened mine I set it at about 1.25" with the stepside bed. I believe it is closer to 1" now with the fleetside, but the front panel is bowed. If you want it correct you have to watch the wheelbase also which should come out to 131.5" if I remember right.

[68 TT]

Originally Posted by bluex

When I shortened mine I set it at about 1.25" with the stepside bed. I believe it is closer to 1" now with the fleetside, but the front panel is bowed. If you want it correct you have to watch the wheelbase also which should come out to 131.5" if I remember right.

You need to be careful tightening up the bed gap too much if you actually use the truck to haul anything or do any kind of off roading. The frame flexes quite a bit and that gap diminishes rather quickly when heavily loaded.

I would hate to see a crease in your cab from the bed rail contacting the cab under load.

[bluex]

Just actually measured it with the fleet bed. On the sides at the body line it is 1", at the top on the bed front panel it is 1.5"

Mine has been like this for about 6-7 yrs now and I have not had any issues with it. I already have a crease in the cab from when I got rearended when it was still a long bed.

Heres how I did mine. I got the shortbed first, set it on the frame. The second set of holes from the tailgate matched up. I put bolts in there loosely to align it, then marked and cut the rear of the frame so it would sit flat. From there I went around measuring bed gaps on all kinds of different trucks and came up with 1 1/4 as what I wanted. I measured from the bed to the cab and came up with taking out the 14". I came 2" off the rear cab mount and made a mark. 14" from that mark I made another one. That was the section I cut out.

I know I'm going to hear crap about this, but I made straight cuts and plated the inside of the frame after it was welded back together. I have had no issues with this and I still use it as a truck every once and a while. For a few years it was my only truck and I actually used it to move to AL, drove it down there full with all my tools and truck parts. It came back to SC behind the moving truck on a trailer, but the bed was full again.

Oh and my wheelbase came out perfect at 131.5 too......

[Conundrum]

Originally Posted by 68 TT

You need to be careful tightening up the bed gap too much if you actually use the truck to haul anything or do any kind of off roading. The frame flexes quite a bit and that gap diminishes rather quickly when heavily loaded.

I would hate to see a crease in your cab from the bed rail contacting the cab under load.

I have thought about that and plan to use the polyurethane body mounts to help thighten it a little more than the factory style rubber mounts would. I know it won't eliminate it but they should help, and I am also thinking of a way to try and stiffen the frame up a little without putting in a roll bar setup. And with it being a 2wd I plan for it to sit to low to really do any hauling other than maybe a cooler and lawn chairs, and i'm not to big on off roading.

Originally Posted by bluex

Just actually measured it with the fleet bed. On the sides at the body line it is 1", at the top on the bed front panel it is 1.5"

Mine has been like this for about 6-7 yrs now and I have not had any issues with it. I already have a crease in the cab from when I got rearended when it was still a long bed.

Heres how I did mine. I got the shortbed first, set it on the frame. The second set of holes from the tailgate matched up. I put bolts in there loosely to align it, then marked and cut the rear of the frame so it would sit flat. From there I went around measuring bed gaps on all kinds of different trucks and came up with 1 1/4 as what I wanted. I measured from the bed to the cab and came up with taking out the 14". I came 2" off the rear cab mount and made a mark. 14" from that mark I made another one. That was the section I cut out.

I know I'm going to hear crap about this, but I made straight cuts and plated the inside of the frame after it was welded back together. I have had no issues with this and I still use it as a truck every once and a while. For a few years it was my only truck and I actually used it to move to AL, drove it down there full with all my tools and truck parts. It came back to SC behind the moving truck on a trailer, but the bed was full again.

Oh and my wheelbase came out perfect at 131.5 too......

Cool, thanks. I'm not to worried about the wheelbase measurement, cause I know that with what i'm wanting to do it will end up a little bit shorter.

[68 TT]

Originally Posted by Conundrum

I have thought about that and plan to use the polyurethane body mounts to help thighten it a little more than the factory style rubber mounts would. I know it won't eliminate it but they should help, and I am also thinking of a way to try and stiffen the frame up a little without putting in a roll bar setup. And with it being a 2wd I plan for it to sit to low to really do any hauling other than maybe a cooler and lawn chairs, and i'm not to big on off roading.

You can really strengthen up the frame by adding a layer of 2"x3/16" steel flat bar to the top & bottom flanges of the stock frame rail. These are the areas that contribute the most to the bending strength of the stock frame.

It doesn't have to be fully welded in place either. Stitch welding by putting down a two inch weld and leaving an inch of open area before the next two inch long weld will cut down 33% of the welding work and minimally impact how strong the connection is. Alternate the open areas side to side on the flat bar so none of them line up across from each other. We do stitch welds all the time in structural frames and fabrication.

[bluex]

I was wrong on the wheel base. 131.5 is the LWB, SWB is 117.5, sorry its been about 6 years since I did it...

[Conundrum]

Originally Posted by 68 TT

You can really strengthen up the frame by adding a layer of 2"x3/16" steel flat bar to the top & bottom flanges of the stock frame rail. These are the areas that contribute the most to the bending strength of the stock frame.

It doesn't have to be fully welded in place either. Stitch welding by putting down a two inch weld and leaving an inch of open area before the next two inch long weld will cut down 33% of the welding work and minimally impact how strong the connection is. Alternate the open areas side to side on the flat bar so none of them line up across from each other. We do stitch welds all the time in structural frames and fabrication.

I haven't really ever thought about doing it like that, it's a good idea.

I was just thinking about getting a large dimple die and some 3/16" plate, put a hole every 1-1 1/2" and basically box the frame in but not add as much weight. The way you described seems much easier and cheaper, as I wouldn't have to buy a die or as much steel.

[68 TT]

Originally Posted by Conundrum

I haven't really ever thought about doing it like that, it's a good idea.

I was just thinking about getting a large dimple die and some 3/16" plate, put a hole every 1-1 1/2" and basically box the frame in but not add as much weight. The way you described seems much easier and cheaper, as I wouldn't have to buy a die or as much steel.

Think of the frame rails as an I-beam with the center web offset to one side. Most of the strength of an I-beam is from the outer flanges. The center web is pretty much only there to keep the top & bottom flanges in place. The strength comes from how far apart the top & bottom flanges are apart and how thick the flanges are.

In the case of our frame rails it is the top & bottom flanges of the frame rail that give it the most strength and is where we can increase the strength since we can't easily move the flanges further apart.

Adding material to the top & bottom flanges of the frame rail will make a huge improvement in bending strength. If you add 3/16" flat bar it will pretty close to double the resistance to bending the frame has and greatly reduce the deflection when loaded.

If you want additional torsional strength to help resist twisting then adding the box plate to the side of the frame rail will increase that.