The initial inspection turned up a Swiss-cheese rear sub-frame. A little rust is to be expected on a 17 year old car, but this was “returning to nature” type rust, not just some surface problem. Fortunately, good used parts are readily available and the whole thing is really held in place by only four bolts. Since you have to lower the rear sub-frame to replace the rear sway bar — which we planned to do anyway — replacing the sub-frame wasn’t that much more of an effort. The bigger question is what else should you replace while you’re at it?
When building a trackable street MINI, we like to start modding with a bigger rear sway bar. The Alta 22mm adjustable bar is a good compromise between price and performance. For a stock sport suspension, use it on its softest setting (which is still 100% stiffer than stock), and go stiffer once you have more negative camber in the front, otherwise all that grip you shift to the front just goes into chewing up the outside edges of your front tires that much faster. It is usually a good idea to replace the end-links at the same time, especially if they’re the original ones that came on the car.
We want to eventually replace the stock suspension with height-adjustable coilovers. With both the first and second generation MINIs, if you lower the car significantly, you will need to adjust the rear camber to prevent eating the inside edges of the rear tires. To get enough adjustability, you will need to add adjustable lower control arms (often called camber arms). There are two main variants of these on the market. The lower price arms have heim joints. These have screw-in metallic or semi-metallic bearings at either end of a long center rod. They offer simplicity, but often have quite a bit of noise. Better are they type with larger rubber bushings and a smaller center knuckles design. They tend to be beefier and less prone to squeaking under load. That’s what we went with. You only need adjustability on the lower arms, so the stock upper arms are retained. Since we were refreshing everything else, we just got a pair of OEM upper arms from FCP Euro along with some new mounting hardware.
Pelican Parts has a couple of good DIY articles for replacing the rear sway bar and replacing the control arms. Though they don’t specifically address the replacement of the subframe, those two articles capture 90% of what you need to know for the job. You will need to support the gas tank as it attaches to the subframe too and those bolts must be removed before lowering it. The remaining bit to research is about disconnecting (and in our case replacing) the rear brake lines. This last bit is important, and don’t proceed with the project if you aren’t comfortable with what it will take to do that. MINI hard lines can get corroded and too much twisting pressure can make them snap. Let soak with penetrating oil first and proceed with caution.
