PDA

View Full Version : Frame shortening?


a87ss305
05-04-2001, 07:24 PM
Has anyone here shortened a crewcab up to use a standard short 6' bed? If my calculations are correct I would need to shorten it exactly 14". I arrived at that length by finding the difference between a short bed wheelbase 117.5" and a long bed wheelbase 131.5". If this is correct and I subtract the 14" difference from the crewcabs 164.5" wheelbase then my new wheelbase should be 150.5". Do these figures look right? Or would the safer bet be to "mock" the whole thing up with the 6' box to see how it looks and then cut accordingly?

85w/350
05-04-2001, 07:44 PM
Chuck is going to be the expert to consult with on this project. I think I remember reading something about the placement of the rear axle that makes this project difficult. If it were me I'd have the 6' box there and then cut. Good Luck!

75
05-04-2001, 07:45 PM
The math sounds right, but I would be strongly inclined to do some "mock-up" work before starting to cut - both to ensure that the "chopping" is planned out thoroughly and to get an idea of how it will look when finished to make sure you will like the result.

Any time you get into mods like this which involve frame surgery, make sure the metal fabbing is done RIGHT - the first time - by whoever does the work! In addition to the obvious problem of frame breakage, there is the less-obvious one of alignment. If the frame doesn't go back together straight & true, the truck will "dog track" down the road and it be difficult/impossible to align the front end properly.

I think you will also have to use shortbox (16 gallon?) fuel tanks rather than the ones on the crewcab now. Your driveshaft will also end up being a "custom" part after shortening to the required dimension.

This is an interesting customizing idea - may be a lot of fun seeing some people :confused: trying to figure out what model it is!

Alan
05-05-2001, 07:39 AM
I've done a frame clip, on a bigger truck, and firmly believe that "measure twice, cut once" is a good idea in this case. What I did was figure how much I wanted to take out, then made two scribe lines on the frame as reference marks. I was cutting out 18", so I made my reference lines something like 24" apart. THEN I made my cut lines between the reference lines. After the 18" was removed I had the reference lines, that were now 6" apart, to use to line everything back up. To keep as much accuracy as possible, use a sharp scribe, not a chalk mark. A scribe line is so fine that it's real easy to get a good measurement off it. It took a while, but I got a straight frame when I was done. I used a cover strip on the outside of the frame, did a full penetration weld from the inside, then ground off the backer strip, gouged out the root pass and welded up the outside, then ground that flush and added a cover plate that was as long as I could fit between the crossmember rivets ahead of the cut to the spring shackles. I clamped the cover plate in place, drilled bolt holes (used as many existing holes as I could) then took the plate off, painted both it and the frame and then bolted it up solid. This gets a little more stress than a pickup frame would, it's on a GMC 5500, 19,500 GVW, and so far it's still together.

75
05-07-2001, 10:03 PM
Alan's described the right way to make a splice connection in a channel (your frame) - here's a true story describing what can happen if you don't do it right:

About 8 years ago I worked for a company that did a lot of structural steel. We were installing headers above the window openings on an addition to existing building. These were made of, as I recall, 8" or 10" channel which weighs around 12 pounds a foot. They were about 15 feet long.

I went to put one up, got one end bolted and climbed up on it to walk across (crane had a hold of it) and sat down to connect the other end.

Next thing I knew, I was on the ground 12 feet below in total surprise. The channel had snapped in half just ahead of where the crane was hooked up. :eek:

Turns out it was spliced together out of 2 pieces in the shop. :mad: No root gap, welded with hardwire (and probably not hot enough either) then all the weld was ground down smooth. There was practically no fusion around the joint. The red oxide primer was providing most of the strength. Without looking closely, you never would have known that channel had been spliced.

Until 170 pound me caused it to break, of course. Fortunately, I landed on soft dirt so I wasn't injured and I didn't see the shop guy who had spliced it until the next day so HE wasn't injured! (I had calmed down by then)

I know this wasn't a truck frame, but the point is that splicing pieces together is serious business - a frame sees a lot more stress than that channel ever would - so make sure it gets done right the first time.

BTW, not too long after that episode I quit & went truck driving for a few years. When I decided to go back to the welding field I did NOT go back to work for the same outfit!

Good luck with the project - keep us posted on progress!