Designing the new rear end

Progress! Well, design-wise. I’ve taken all the tied up pieces off the truck, and started to take it apart further. The first major project will be the rear drive set-up. The rear now looks like this:

Back to front: the rear bumper bar is missing, then there is the first cross member, then we see the axle, then the second cross member. The first and second cross members are mounted at the location at which the current leaf spring suspension is mounted to the frame. Yesterday I measured a lot and made a sort-of template of the frame to copy to CAD. I first cut a piece of cardboard to fit around the suspension mounts:

 

This cardboard I mounted to the frame:

 

 And with a black marker I traced the frame:

 

I did both the left and right hand sides, because it seems the truck is not perfectly symmetrical. You can see the left hand side tilts inward, I measured 8 degrees:

The right hand side only tilts in 3 degrees:

This means the new sub frame will also need to be a-symmetrical to fit right, and to have the IRS unit mounted central to the main frame.

At home, I transferred all dimensions and the traces to CAD:

So, here’s the first sketch of what I am going to build as a rear axle sub frame:

I will make a simple new rear bumper bar. Both original cross members will be replaced, and mounted to the frame with flanges using the original holes to which the leaf spring suspension was mounted. There will be a new third cross member, to which the IRS diff will be mounted. The cross bars I hope will add a lot of strength / rigidity to the frame. Because currently the frame is very flexible. All cross members and bars will be sheet metal, U shaped.

Please feel free to comment.

Hugo