Chassis - Chapter 1: Page 6 (April 2001)


Unlike, say, a T-bucket frame, Model A chassis rails do not run straight from front to back: they taper out slightly from the front crossmember back to just behind the A-posts (front door posts), then kick out again at a wider angle all the way back to the rear crossmember.

A nip and a tuck . .The actual angle of this step, about 54" from the front axle centreline, is around two and a half degrees each side: this is achieved with a small pie-cut in the outside edges of the rails. The front section is clamped to the chassis jig, and the back end is spaced up 2", then the joint welded. The actual distance should be 2-1/4", but after the weld cools (we used a TIG-welder for a stronger joint), it shrinks and lifts that extra bit.
Because we are planning to use a '40 Ford-style rear spring that mounts 6" behind the axle instead of over it like an original, we need an extra few inches at the back. We mentioned earlier, on Page 2, that we had allowed an extra six inches or so on the rails for a hefty kick-up at the rear. Now we're keeping the chassis straight, and we can use the extra length to set the spring back (we still had to add a couple more inches to the ends). Original chassis rails would meet the arched rear crossmember about 1-1/2" in front of the axle centreline, so we are making our extensions run parallel to one another from this point back, to keep the overall width within stock dimensions. Another pie-cut, another weld: repeat for the second rail, then they're ready.

. . another nip and a tuck.While mocking up the chassis and checking dimensions, we concluded that the outer ends of the front crossmember leading edge projected too far in front of the axle centreline. This was probably because of the way we tilted back the centre section for the spring mount, and to avoid any clearance problems with the grille shell in the future, we cut a couple of wedges out of the top face, tweaked the front edge back, and welded it up.
In the photos it has been trimmed to the right width for the chassis, and is ready for installation.

This bit bolts on.Model A's didn't come from the factory with a front spreader bar - they didn't need one behind the bumper - but it's almost compulsory for a fenderless hot rod. The chassis is two inches deep at the front of the frame horns, so a length of 1-3/4" diameter tube fits just right: just cut the ends at a slight angle to match the chassis taper, then weld a couple of threaded plates on the ends.
Er, well, it should have been easy. A momentary brain fade caused a slight mis-calcuation, and we ended up with a spreader bar a half-inch too short! We had welded a 3/8"-UNF nut behind each of two 1/8" plates (remembering to drill a clearance hole first), a round one for one side, and a squared-off one for the other. These were in turn welded to the tube, the squared one to prevent the bar rotating inside the rails.
When we realised that the bar was too short, a quick search through the offcuts bin turned up two 1/4" thick discs, just the right diameter to weld to the ends to correct the error. Oh well, you're supposed to learn by your mistakes!

That's it, ready for the chassis now!