There are many reasons the E90 Brake Booster belongs in an E30, for the same reason a 24-valve BMW straight six belongs in them. The E9X booster is compact, powerful, abundant and affordable. Because the E9X is a much larger and heavier vehicle, this booster assembly packs a punch. They made over 3 million units of these cars, these boosters are littered in the market, making it a very cheap acquisition. Being from a newer generation, the booster and master design are also superior to the original equipment or other Porsche inspired conversions. It’s compact size really frees up critical space in the BMW E30’s engine bay.
Another benefit of running a BMW alternative part is that it bolts right up through the firewall and onto the original pedal-box assembly. You just need a custom pin to match the width of the newly introduced clevis from the E90 part, as it is wider. I sell the Custom E90 Brake Booster Clevis Pin in my store. Now you can clear the intake manifold to a 24-valve BMW engine. *As long as it does not have individual throttle bodies; S54 engines require more clearance in this region and unfortunately the booster needs to be slightly relocated. Half an inch (0.5”) over to the driver’s side plus 1.25” downward is the amount that you will have success with. Results may vary due to some variables like engine mounts used and tolerance stack-up, so make sure you test fit everything to ensure all components are happy and have ample space – however these relocation values have worked for over one hundred of my customers.
Brake Master Cylinder:
The outputs on the E9X master cylinder are inconveniently on the opposite side. Easy solution though, grab yourself a first-gen (E83) X3 master cylinder. A euro E9X booster will also give you the same result. The brake line fittings have effectively been changed from M10x1 thread to M12x1 relative to the original equipment. Keep that in mind when planning out your bubble fittings on your newly created brake lines. The output closer to the driver will go and T-off to meet FL and FR calipers. The other output goes to the rear. T-Fitting Product Listing
If you are running ABS, this fitting above will not be necessary.
Miscellaneous Parts:
Doing a remote reservoir for the braking system is also another step of the process, a clean mounting solution on the driver side’s strut tower is in my store: E30 Brake Reservoir Relocation Bracket. It is intended for the 2002 (E10) Brake Reservoir (#34321112399). Alongside some small fittings that are listed here: Misc. Parts for BMW E30 Braking Conversion
*S54 Specific Information:
The relocation may seem daunting but its pretty straight forward, stick to the guide and it will work out like a breeze. The pedal box bracket will need to be extended on its bottom side to accept the change in position of the holes.
It is recommended that you weld up the now useless large hole that was previously used by the booster and bellows boot specifically, on both the pedal box bracket and firewall.
Now that the booster is relocated, the attachment point of the booster to the pedal must be relocated as well to compensate. A small steel cylinder can be welded on the brake pedal to suit the new geometry of the E90 booster clevis. Note that the other fork of the clevis sits on inside of the pedal.
The Blue arrow shows where the E30 booster originally mounted, the Orange arrow shows the newly welded feature that will now connect to the E90 booster's clevis.
If you have any questions or concerns, please Contact Me. Thanks for the visit!
-Pasha