The untimely demise of my old 128 has made me VERY wary of the structural integrity of the unibody, particularly when driven as hard as I drive mine. My old 128 had a nasty habit of spitting the axle out of the differential when cornering hard, or even when downshifting from third to second gear. After I put the car to rest and stripped it of all mechanicals and wiring, I discovered a nice big crack where the "frame rail" goes into the firewall. This was allowing the unibody to flex enough that the axle would pop out of the differential.
In order to help alleviate some of the stresses on the unibody while cornering, I designed a strut tower brace for my second 128. The brace is designed to keep the strut towers from flexing toward each other under load. Repeated movement in metal can cause failure due to fatigue, which is quite undesirable when that metal holds the front end of your car together. Also, if the unibody is flexing, it isn't allowing the suspension to do its job properly so the car will handle worse.
I set about coming up with a design that would be light, rigid, and fit in the confines of a 128 engine bay. In order to have a solid bar go from strut tower to strut tower in a 128, you have to get around the air cleaner, heater box, and spare tire. Additionally, there is not much clearance between the hood and the strut tower tops when the hood is closed.
A small free-flow air cleaner is a must in order for the brace to fit. There simply wouldn't be any way to fit a bar between the stock air cleaner and heater box. Even with a free-flow air cleaner, the space is still restricted, so I had to be careful about where I had the brace run across the engine bay. I decided to use 2x1 inch rectangular aluminum tubing (1/8 inch wall thickness) for my bar. 1 inch round tubing would probably be easier to use, but since I was using aluminum I wanted it as big as I could get. Plus rectangular tubing looks cool :) The spare tire had to come out because the brace would hit it otherwise (like I said, not much clearance under that hood).
With a bunch of clearance measurements and strut tower angles in hand, I set off to the computer lab to design the bar in CAD. Designing parts with CAD software is great because it takes a lot of guess work out of the design/fabrication process. Throughout the whole process I never had to make any additional pieces due to a poor measurement. The only flaw in my design was not leaving enough space for one of the bolts (I wanted to be able to remove the brace w/o removing the brackets from the strut tower tops) to clear the heater box, so I had to cut a small piece out of the box. The brace is incredibly light! Everything is aluminum (polished so that's why it's so shiny) except the bolts, and though I haven't weighed it, it's about the same weight as the plastic grille on my car.
Here is a pic of the brace and the design drawings:
 |
 |
 |