A Pilothouse Design Problem - In Old Age As It Were . . . . .

[grey beard]

A Pilothouse Design Probllem

When Pilothouse trucks are assembled, the pickup beds are already complete units, which are attached directly to the vehicle frames using six ½ x 6-inch long carriage bolts. These six bolt heads are visible inside each pickup bed floor, where they stick up from the outermost floor boards, three on each side..

The problem this assembly method causes is that these six ½-inch bolt holes are factory drilled into the vehicle frame flanges – the horizontal portion of the frame that should never be drilled or welded. Any good automotive design engineer would tell you that the proper way to secure these beds to the frame rails would be to rivet a bracket to the frame web – the vertical portion of the frame proper - and then bolt the bed to these brackets.

Imagine my surprise when I was installing my fuel tank and looked over at my driver’s side frame rail and saw a major crack in the frame. This crack originated directly through this 1/2 –inch hole in the flange and continued more than half way down the six-inch vertical face of the frame web. The truck had been operated in this fashion long enough that the two edges of the crack had overlapped at the top of the crack, causing the entire driver’s side frame member to sag at this point – immediately underneath the front bged crossmember at the left front corner of the bed.

When I put a piece of cribbing underneath this crack and jacked the vehicle at this point, the frame flexed noticeably and then made a loud “pop” as the overlapping ends of the crack came apart. After we clamped the crack into proper alignment, my newly-installed running board on that side had a huge hump in it from where I had shimmed it to keep it level – the rear running board bracket was actually half an inch lower than it should have been due to this crack and the sag in the frame rail. Now if I pull these shims out, things will be much happier in this department.

We will repair this crack with a mig welder operated by an experienced man – not myself – and then add a ¼-inch thick steel plate inside the frame. This support will be bolted directly into the frame web and a hole will be drilled for this front bed attachment bolt to pass through the patch flange as well. Normally frame patches are never drilled at the flange points, but this one is already in position. The patch will be keystone shaped to avoid any square corners that might cause stress to an already-weakened frame rail. Since this truck will likely do little heavy hauling in the remainder of its life, this should suffice.

Just wondered how many other Pilothouse trucks are running around with this same problem – cracked frame rails - with the owners ignorant of the possibility. The cracks could occur at any of the six bed attaching bolt hole areas where the frame flanges are drilled. Mine just happened to take place where I was able to see it. Next time you crawl underneath, your beastie, might wanna’ scope out these six bolt points on your frame rails. JMHO

[Merle Coggins]

The frame on my truck is OK, but the parts truck that I have does have a repaired rear frame. It cracked at the front spring mounts, on both sides. This truck is a cab/chassis and probably had some sort of flat bed at one time. There was nothing on it when I got it. Someone did a poor job of repairing it, but I don't care as I have no plans to put this one back in operation.

[Don Coatney]

Years ago when I was fresh out of High School I worked for International Harvestor at there truck sales processing center. This center was responsible for customer custom modifications. We did several truck frame length changes. We were instructed to never under any conditions drill any holes in the top and bottom frame rails. When we did frame modifications we always used a "fish" plate to give the frame extra strength. Suggest you might do the same to make the crack repairs. Cheap and easy to do.

[Young Ed]

Broken frames seem to be somewhat common in the 39-47 trucks too. I've heard its more common with the prewar trucks and that postwar the frames were beefed up a little. Dads 40 had a huge I beam thing bolted under one side of the frame and when we looked close was broken on the other side. His broke right at the gap between box and cab. After we removed the body parts he cut the U bolts off that I beam and the frame broke in 2. Now the replacement work truck for the cabin a 46 pickup has a break in the frame too. Dad bolted a piece of U channel to the bottom of the frame with the bottom of the U against the bottom lip of the frame. Its been holding for years and we pile that truck to the roof or higher with brush and logs etc. So your plan sounds great for fixing that crack.

[JoelOkie]

Co-incidentally I am currently cleaning up the frame on my b1b, and I have also noticed two small "stress" cracks at the exact location of the frame as the repair in Merle's pic. These cracks are still in the hairline stage (barely perceptible). Given the location of these cracks what would be the correct/best fix? Being situated directly over at the junction of the front of the spring shackle holder and the crossmember there is no way to get a fish plate on the inside, and if put on the outside would space the spring mount out of alignment, plus the plate would also have to have holes drilled. I am left to think it best to simply be welded, and hope for the best. Only other option I see is to weld a thick strap on top, but would that add any appreciable strength?

I have restored a 46 Ford pickup, and have noticed that the steel used in that truck is for lack of a better term, "brittle", especially when compared to a 48 Ford, (which I have also worked on.) and I'm not just talking the frame, as I am not sure about that per se, but the sheet metal to be sure. I suspect that the models just after the War used tin that was largely in content melted down old model T's, and similar stuff. I am new to Dodge truck restoration, and one thing I noticed immediately is that the sheetmetal in this truck welds and works much easier than the 46 Ford pickup. Joel

[woodscavenger]

Mine has cracks that were repaired on both sides.

[Bob_Koch]

Interesting as mine was cracked on the right, just before the spring mount. I thought it was just my truck.

[grey beard]

Welded the frame crack today at the point where the left front bed-to-frame bolt goes through the frame flange. These frames are only 1/8-inch thick. I'm thinking they are the same stuff automobile frames were made of back in the day . . . Hope the rest of you check yours out at these points before you haul very heavy loads. Before we welded this crack the frame really flexed badly at this point if I jacked it anywhere near that area. Imagine what it would do with a load on uneven ground.