With the frame completed, the first dynamic parts could be constructed. Assembling the rear suspension requires welding the upper and lower control arms, welding the rockers, preparing the used Miata uprights, welding on brackets, and bolting it all together.
The rear upper control arms consist of two curved 1-inch tubes, one gusset, and one bent bracket. After over-cutting and bending the tubes, they were placed on a 1-1 scale printout.
Using the layout, the tubes were cut to the right size and angle. The gusset piece and bent bracket were jigged, tacked, and welded. Tube-end weld nuts were welded on and rod-ends were screwed on. Finally, the bolt that interfaces with the upper bushing on the rear upright was added on.
The rear lower control arm was fabricated similarly: bending tubes, cutting to size, and welding according to a printed layout.
The polyurethane bushings and brass sleeves were left in the freezer overnight to make install easier. A C-clamp was used to slide them into the 1.5″ ID tubes on the lower control arms. Rod-ends and jam nuts were screwed into the weld nuts. To link the control arm to the upright utilizes a long 9/16″ steel rod instead of a bolt. After cutting the blank rod to length, a 9’16”-18 die was used to thread the last 3/4″ of each side. The upright’s 14 mm holes were bored out up to 9/16″ and a couple jam nuts were added on each side, as to allow adjustment tightness against the bushings.
With both control arms done (with exception of the brackets for the pushrod and sway bar), the old Miata uprights were to be prepared. They started dirty and rusted with unnecessary dust covers and grease-oozing bearings. After pressing out the old hubs and bearings with an arbor press, the dust covers and bearing seals were removed. The uprights and hubs were sandblasted to remove the dirt and heavy rust and then wire-wheeled to clean off any further corrosion.
After a washing with soap and water and then acetone, the uprights were painted with a coat of enamel primer and two coats of metallic silver, making sure to mask off the inside face into which the new bearing will slide.
When pressing in the new bearings, a steel tube with a diameter a little smaller than that of the bearing was used to keep the load on the outer race and prevent pitting of the ball bearings. After replacing the internal C-ring and adding a new inner seal, the sandblasted hubs were also pressed on, using a bit of oil to prevent seizing.
The pushrod and rocker arm were fabricated next. The pushrod consists of a short piece of tubing capped on both ends by a weld nut and rod-end. The rocker arm was constructed from 4 waterjet-cut pieces. The parallel plates were bolted together before welding to ensure that the bolt holes would line up. The completed rocker arm can be seen below.
Using measurements from the CAD model, the waterjet-cut suspension pickup brackets were tacked and welded to the frame. Also, the brackets for the rocker arm and damper pivot were tacked on. Once the control arms were bolted on and attached to the upright, the pushrod, rocker arm, and damper were installed. The wheel was installed to check clearances. At this point, all components of the rear left suspension are tacked in place, with the exception of the sway bar.
The same process was repeated for the rear right components. After a measurement and symmetry check, all brackets were welded into place.
PH-571 