Aluminum Differential Upright
The stock steel uprights supporting the rear of the rear lower control arms have been replaced with an aluminum plate. My reasoning for this was my attempt to organize and simplify this part of the car. The stock uprights, I felt, were less than adequate for the racing usage I was wanting, plus, I wanted to eliminate the differential support that bolts onto the differential cover, and crossed both of these uprights and attaches to the chassis via rubber bushings. In addition to this, I also wanted to provide a means of attaching a rear swaybar to the uprights, instead of to the body ahead of the axle, behind the seats. To be able to do all these things, and simplify it, I needed to make a single part for all the above items to be attached to (differential, swaybar, and rear lower control arm).
The piece I made is made from aluminum plate, that replaces the steel uprights, by using the same attachment points as the existing steel uprights did. The top of the plate has 1" angle aluminum welded to it to allow the plate to be bolted to the chassis with the original four 8mm bolts used to attach the factory uprights, plus I used two 14mm bolts that the rear differential mount used, to reinforce the outside ends of this plate, for a total of 6 mounting bolts. I then attached the factory steel crossover brace to the bottom of this plate, again using existing factory located holes and bolts, and then simply attached the lower control arms to this brace just as I would have if I had used the factory steel uprights. Also the spacing came out so well, that I was then able to solidly bolt the differential (cover) to this aluminum plate (no rubber bushings) in the factory (fore/aft) location, thus eliminating the spring steel rear differential mount and rubber bushings. I wish to note here, that I raised the differential 1" to lessen the angularity of the halfshaft U-jounts caused by the lowering of the ride height. I wanted to raise the differential even higher, but the chassis crossbrace directly over the differential case caused interference to any higher raising of the case, unless this crossbrace was cut out, which I chose not to do this for concern of the unibody rigidity. See the "Halfshaft" section for further comments about the halfshaft's potential problems and their remedies.
Lastly, I attached the rear swaybar brackets to the outside edges of this plate (This plate is wider than the original distance of the original uprights, by 4" per side, to make the most use of a custom made swaybar; see "Swaybars"). With the front differential mount solidly bolted to the chassis, the plate now has much more lateral and longitudinal strength than the factory setup did. The aluminum also acts as a great differential heat sink if holes are cut in it allowing air to flow through the plate. I only saved about 2 pounds with this modification, but gained great rigidity in this area of the car, and greatly simplified the way this was put together.