Helper Springs
 

I was looking at the Jeg's catalog, and they have helper springs on special for leaf spring trucks. But, the design looks like they could put additional stress on the trucks leaves. These sit on top, and a U bracket loops from the helpers to the underside of the stock springs with a flat piece of steel and nuts.
The helpers I had in another F150 I had literally bolted to the top of the axle and the brackets bolted to the frame just below the box. As the truck started to sag, the brackets made contact with the leaves and helped keep the sag at a minimum. I don't know if those helpers I had were factory or not, but they worked great when towing. I'd love to find another set like that for my '89 Ext. Cab.:thumbsup:

What you had before were overload springs.

I had the factory overload springs on 2 F150s. Pic is from my current:

https://cimg4.ibsrv.net/gimg/www.f15...922e1c429a.jpg
https://cimg3.ibsrv.net/gimg/www.f15...40957b7129.jpg

Gotcha. Can you still get these? Or are they discontinued? If not, I guess I'll go to air bags.