Turns out the Bilsteins that were already installed on the car were the exact same part numbers as the ones we're putting in. We'd feel worse about this if dampers weren't a wear item. New for the win.
Our project BMW came pre-equipped with a useless (to us) 4.10 open diff, and we decided that mounting the new rear anti-roll bar would be easier with no differentials in the way. This was as good a time as any to perform the swap to our class-legal 3.73 OEM limited-slip diff.
Brake pads of unknown origin and questionable usefulness were replaced with Carbotech pads.
For maximum efficiency and some unintentional bling, we installed a set of Carbotech-sourced brake rotors.
We had to swap the vehicle speed sensor from the 4:10 diff to the 3:73 because the plug shape was different. Per seems to want to eat the sensor.
A rear anti-roll bar from Ireland Engineering is much beefier than the wimpy OEM unit.
The rear anti-roll bar mounts are robust aluminum pieces that bolt up to the chassis and include reinforcement plates that drill into the trunk. Unfortunately, our kit came with some improperly-sized bushings; the new ones are on the way, and it should be a fairly easy task to swap the bushings.
With the bar in place, Per muscles the 3:73 limited-slip differential into place with the help of his friend Jack.
Pink hearts, green clovers, red springs, yellow dampers and blue swaybars! They're always after me Spec E30!
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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