I had Detroit Spring make me a set of four, 1 3/4" wide custom springs.
I had to weigh the truck in " as driven condition ", meaning all the weight it's going to have on the tires when going down the road, including fuel, the driver, passenger, and any luggage. I used race car, four wheel digital scales for super accurate measurements. The weight was split 50/50 front to back and only slightly heavier on the left then the right, had I been building a race car I would have been pretty happy with the measurements!
I then put the truck frame on stands and unhooked the rear shackles and shocks so the axle was back on the scales. This weighed the axle, tires, brakes, shocks, half the leaf springs, and half the driveshaft. I then moved to the front and did the same thing. The spring shop needed to know how much weight the springs were holding up and how much was unsprung weight ( everything below the springs). Doing a little math I figured out how much was above and below the springs.
Next I removed one front and one rear spring. I places a small round axle or bar in the ends of each spring, added bearings to the bars so the axle would roll with no drag, think of a skateboard. I had my Toyota truck jacked up in the rear so I could get the springs under the back of it. I placed the spring centered under the trailer hitch of the Toyota. I placed one of the scales between the hitch and the spring, then slowly lowered the truck down till I compressed the leaf spring one inch, measuring off the garage floor, read what the scale showed to see how weight it took for one inch of compression.. This gave me the spring rate of the spring I had been using. I have the numbers wrote down somewhere, but the new spring have a rate about half of what I was using. Factory '37 front springs are something like 490 lbs per 1 inch of compression.
The new springs are much softer, had the same ride height, have teflon buttons on each leaf, and they supplied all the correct attaching hardware. This was quite a while back, 10 years maybe, so cost has likely gone up. My total bill was around $1200 after shipping was added, spring averaged $250 each.
I had two choices, sell the truck and buy something that rides better, or fix what I had. New springs were the cheaper option. I am real happy with how rides now, '37s are short wheelbase and don't weight much, so it rode like a Jeep with heavy springs and shocks ( a lot of front to rear bucking ). It's now much closer to a car than truck, so hauling loads is out, but I never intended to haul gravel anyway. I did add a front sway bar since the truck was now softer riding, it tended to lean more in corners then I liked. The bar helped restore the stability.
No matter what springs you use, you need to know how much weight they are going to hold up. Sprung weight and unsprung weight is a must know item. The guys at Detroit spring were super helpful, ask a lot of questions about what I wanted, then came up with springs that worked. I can always send mine back for service if needed, they keep good records and can replace, repair, or update pretty easy.
