Since we had to replace the rear differential at some point and since the rear anti-roll bar is situated above said differential, it made sense to pull the diff, install the rear anti-roll bar and then install the new diff.
With most of the interior work completed, it was time to start swapping out the parts that you can’t see with the wheels on. The bulk of the work we had to do involved the rear suspension on the car, so we decided to start with the back. Our box of goodies included springs, dampers, anti-roll bars, brake pads and rotors, and an OEM limited-slip differential.
Spec E30 rules dictate exactly what Bilstein dampers are legal (Bilstein Sport P36-0335 or P30-0334 for the front, and B36-2027 for the rear). Ireland Engineering makes some nice upper mounts for these units, so we installed these along with the dampers (these are currently on sale for $75).
The springs are also specified by the rules as H&R Race Springs part number 50404-88. The nice thing about race springs is that they’re shorter than the OEM units, so the cute little coil beehives popped right in to place without any spring compression struggles.
Our BMW 325is came with an open 4:10 differential from a 318 already installed. The class rules require that we run a 3:73 OEM limited-slip differential, which will be better for our needs anyway. Since we had to replace the rear differential at some point and since the rear anti-roll bar is situated above said differential, it made sense to pull the diff, install the rear anti-roll bar and then install the new diff.
While Per wrestled with the diff, Scott swapped the generic-looking brake gear for some trackworthy pads and rotors sourced from Carbotech. Once the diff was out of the way we installed the Bilsteins and the rear anti-roll bar, which required a bit of drilling since the Ireland Engineering brackets have reinforcement backing plates that mount into the trunk. It’s a much stiffer bar, and you wouldn’t want it tearing through the OEM mounts under load.
The rear diff went in with a pretty standard amount of stubbornness for a huge lump of iron, but at the end of the day we had a Spec E30 that was moving under its own power again. Also, it’s riding kind of low in the back right now. The front suspension and brakes are next on the list.
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