Kool Stride help

[nlg8479]

I bought a used Kool Stride double jogging stroller, and I can't seem to figure out how to reassemble it. I have the two pins placed that secure the rear frame, but there is a U shaped hook with a pin on both sides. I can't figure out what it is supposed to do, and I am afraid to run with the stroller until I work it out because I don't want it to fall apart . . .

Help please!

Much thanks.