Lately, I have been back on pondering about how to make my 257 heavy duty enough to handle the 15 ton rollback. One of the specs that Jerr Dan recommends for the 15 ton rollback body is the frame must have an RBM spec of 3,000,000 in lbs. I did some search on frame rails and found a place called P.G. Adams located in Burlington, VT. So far, they are eager to help me in determining the proper frame rail. We've gone over few scenarios over the phone and then they quickly fax out drawing with specs of the rails.
Of the scenarios we came out with so far, they are all double frame. We were speculating that grade of the original frame was (at most) 80,000 psi steel. It was recommended to stay with the same grade.
Using grade 80 steel would have to be 3/8" thick and 10 3/8" tall on the outer rail. The inner rail with a height of 9 5/8" is closer in dimension to the original frame which is 9" tall. Grafting might be a problem. A bigger problem will be doubling the frame with the inner rail as the main. The outer rail is 3/8" thick which will move out my spring hangers and such by that 3/8" on each side. I'm sure more problems will arise if I were to go this route. The RBM of this set-up was 3,040,000 in lbs.
Using grade 100 steel she was able to meet 3M RBM and have a height of 9 1/4" on the outer rail. I think this would graft to the original 9" frame much easier as it will only have an 1/8" step on the top and bottom. In this scenario the main frame is the outer rail which will not disturb suspension mounts and other component locations. The one issue that had come up with using grade 100 steel is it's compatibility with the lower grade of my original frame. She said when combining grades the figure of the lower grade must be used to calculate the RBM. The RBM would be too low if we used grade 80 with these dimensions. I mentioned the remaining section of original frame will only comprise about 1/8th of the total frame length. The majority of the truck is going to be grade 100. She said she could only go as far as calculating RBM and recommended calling one of the truck frame specialists that they do a lot of business with to ask for some advice on mixing grades.
The sections of frame that I am planning on installing will be about 30 feet long. It makes the most sense if I am going to have the cab off the truck to go as far forward as possible with the new double frame. About one foot in front of the front leaf spring's rear hanger looks like a good place to cut. A little ways ahead of that area the frame begins to taper. In the picture below, the cut will be somewhere between the air brake hose and the pitman arm bracket. This will leave about 4 or 5 feet of original frame.
I feel having the double frame going far enough forward to have the spring hanger bolted though both rails would be much stronger than grafting behind the cab.
I know double frame needs to be able to twist and have some flex so you cannot weld the rails together. But, for long sections where no hangers or anything are mounted, would I need to install bolts and nuts to hold the faces of the rails together? Is it worth trying to paint between the rails before they are assembled together? Any idea on spacing between crossmembers to determine the correct number of crossmembers?
Anyone have recommendations or know where I can find some literature in properly setting up this frame project?
thanks in advance,