Buying an older vehicle to turn into a race car usually means that you're buying a car with old, worn out parts. No matter how old your car is, it's absolutely vital to be as thorough as possible when looking over the car prior to racing it. Inspecting things such as the rear subframe and its bushings is important because they are critical components that support the differential and rear suspension. On an E36 BMW, it is common for the factory rear subframe bushings to deteriorate causing the rear subframe to shift and clunk under load.
This shifting and clunking can result in alignment problems, added stress on suspension components, drivetrain vibrations, cracks in the subframe, and worst case scenario, the sheet metal where the subframe mounts to can actually start to tear. To rectify the latter, BMW came up with reinforcement plates that get welded onto the body where the subframe mounts. Most E36 M3's came with these reinforcement plates already installed from the factory with the exception of some early '94 models. All non-M E36 models did not come with these reinforcement plates and it is highly recommended to have them installed if you plan on racing the car in any fashion.
The rear subframe also houses another item that needs to be closely inspected, the front differential mount. The front differential mount is pressed into the subframe and like all of the other bushings, it goes bad over time. When the front differential mount wears, it puts extra stress on the front differential bolt. This stress can lead to the bolt bending and even completely breaking if left ignored.
Another concern with the rear subframe deals with where the sway bar mounts. The sway bar is mounted to the rear subframe with two tabs out towards the rear corners of the subframe. The tabs on the subframe are known to tear due to the stress put on it from the sway bar. There are aftermarket Rear Sway Bar Reinforcement Plates available to strengthen the tabs so that you can run any size sway bar that you want without a worry.
The subframe in my E36 M3 had almost every issue listed above. Upon inspection, I found several cracks in the subframe, torn sway bar tabs, and a bent front differential bolt. I had Adam at Final Fabrication and Repair fix all of the cracks and install the sway bar reinforcements before I installed AKG Motorsport poly subframe bushings, and poly front differential mount. With a new front differential bolt from FCP Euro, this subframe is ready to be reinstalled!
