How To Build a Model A Hot Rod Chassis

 

I decided to utilize a complete 1950’s “Dago” Dropped axle with “juice” (hydraulic) brakes and split wishbones I had stashed away. I removed the cobbled together front spring and installed a nice reverse eye dropped “Super Slide” spring from the guys over at Posies Rods and Customs. They were nice enough to make me a set with the ends rounded and hidden super slide pockets so that once they were painted up they could pass as an old modified part with the performance of their high end springs.

I also mounted up the desired size wheels and tires I wanted to run on the car. These items MUST be decided ahead of time so that you can mock everything up correctly before making any major changes. On this build I’m running 750-16 in the rear and 6.00-16 in the front.

How To Build a Model A Hot Rod Chassis

How To Build a Model A Hot Rod Chassis

How To Build a Model A Hot Rod Chassis

With the back half of the chassis on jackstands and leveled out I dropped the body over top of the chassis and rolled the complete rear axle with the cross member mounted to the spring under the body. This allowed me to fine tune the amount I wanted to channel the body over the frame. I then temporarily mounted the drivetrain to weigh the front end down to get an idea of the final front ride height. This allowed me to set the rake on the frame and body without it changing too much once the car was assembled.

How To Build a Model A Hot Rod Chassis

Now that the body height was set and the rear wheels were sitting where I wanted (in my case I didn’t need to block them up), I took measurements from the top of the frame rails to the top of the rear cross member. This gave me a measurement of how tall my rear frame step was going to be. I also stood back and checked to make sure the wheel base looked good and did some minor adjustments to get the wheelbase measuring what I wanted (just slightly longer than a stock ’32 Ford V8 wheelbase). I noted all of these measurements and took everything back apart so I could mount the chassis back on the table.

How To Build a Model A Hot Rod Chassis

How To Build a Model A Hot Rod Chassis

How To Build a Model A Hot Rod Chassis

After setting the chassis back on the table we used mechanics wire to cross measure where we’d be cutting the back half of the frame for where the rear step would start. I chose to make it start just behind where the rear firewall would be so that when the car was closed up you wouldn’t see the large step (but we did lose most of our trunk space).

I cut 45 degree angles into the rails at these measurements and tack welded the entire chassis to the table so it would’t move during this process.

How To Build a Model A Hot Rod Chassis

We then took our frame rail to rear cross member measurements and built a fixture that put the top of the cross member at the exact height we wanted and tack welded the cross member to the fixture. We then set the rear cross member so that it matched our wheel base and cross measured from the front cross member to the rear cross member to make sure the wheels were straight.

The fixture was then welded to the table to lock in the rear cross member. This step is important to do two or three times to make sure the vehicle drives straight and doesn’t “crab” down the road!

How To Build a Model A Hot Rod Chassis

How To Build a Model A Hot Rod Chassis

How To Build a Model A Hot Rod Chassis

At this point it’s as simple as connecting the dots to make your rear frame step. I first measured out the shape of the end of the cross member into a piece of tubing and notched out the bottom of the tube so it fit over the cross member.

I then took the drops from our rear 45 degree frame cuts and clamped them in place so I could lay another piece of tubing across the cross member to see how long the leg of the step needed to be and where the pieces intersected. This allowed me to draw out the 45 degree cuts for these two pieces.

How To Build a Model A Hot Rod Chassis

I then beveled all of the joints and clamped the pieces in place. I adjusted them one final time until the steps were even and square on both sides. With everything measuring correctly I fired up the MIG 175 and welded the rear step up and finally to the rear cross member. I will be adding wedges or braces to the corners of each joint when we tear the car down for final welding and paint prep.

How To Build a Model A Hot Rod Chassis

How To Build a Model A Hot Rod Chassis

With the chassis all welded up we could cut it free from the chassis table and assemble the suspension. Of course admiring the frame only lasted for a short time before we HAD to mock the body and engine back up to really get a good look at how the car was going to look!

How To Build a Model A Hot Rod Chassis

I’m really happy with how it sits and with some small adjustments as we build the floor, I think it is going to have a really great stance!

Now that the body and drivetrain are mocked up I can start making cross members, engine/transmission mounts, and radius rod mounts for the frame.

This tech article is meant to inspire and give you a jumping point for building your own chassis. Every car is going to be a little different in measurements and execution, so be sure to think it all through before you start.

Also make sure that you’re confident in your welding skills before tackling a project of this magnitude, the aim is to build a strong AND safe vehicle! Keep an eye out for future tech pieces as I build up this little A Coupe this winter.

— Matt / Eastwood 

Source: https://garage.eastwood.com/eastwood-chatter/hot-rod-chassis/