A big drawback of the pre 1960s NAPCO trucks is that the frame was designed for 2WD front suspension. When the 4wd NAPCO axle is installed: the front suspension loses about 1.5" of up travel due to the leaf spring plate/bumper on top of the axle. Combine this with saggy old springs and you're left will less than 1" of suspension travel. Not cool for washboards or any type bumpy driving.
So, I'm thinking about notching my frame by 1.5-2" and have done a lot of thinking about how to reinforce the notch.
Geek alert!
... the computer is helping me think
Attached pictures show the two strategies I'm considering:
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https://imgur.com/nZhKwa4[/img]
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https://imgur.com/etd3Odp[/img]
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https://imgur.com/3nA5uDX[/img]
It turns out that the 'arch' design with reinforcement on top is stronger for suspension bottoming (on a bumper in the notch) yet weaker under normal conditions.
The 'fishplate' design without upper reinforcing is stronger for normal conditions, but is much more stressed during suspension bottom out.
I'm leaning towards the 'arch' design since I think the loads will be much harsher in the bottom out condition.
Note that the stress numbers and loading is purely comparative between notched and stock chassis an aren't totally realistic.
However I think its a reasonable way to compare the chassis reaction to the different load situations.
Let me know what you guys think!
