B48D / B58D Alternator Overrun Pulley

These sold out faster than we expected. We have more in production but won’t be available until roughly Aug 31. If you order one for back order we will ship them ASAP. Please read below about potential early B58 fitment issues. If your alternator has a 24mm nut holding on the stock pulley then this part will not fit. We are coming out with a part that will fit. Please email us a VIN if you are unsure. The Alternator Overrun Pulley for the B48/B58 allows the alternator to freewheel when the engine is trying to decelerate. This has many benefits. It saves your crank balancer from trying to tear itself apart and also makes the engine run smoother and shift more rapidly. Longer writeup coming soon. Also fits the Alternator of the B48C transverse engine in the MINI as well as the B38 however there are many variations of this engine in different chassis so we have not been able to verify every possible variation. There are many variations of the correct alternator but if the following is called out for your car in realoem then it will fit: 12318634167 - B48 and B58D (330i, 340i etc) 12318627125 - F56 Mini and other Transverse B48s We are currently unsure on certain early B58. We know it will not fit alternators of the following part numbers: 12318571357, 12318571358, 12318614276, 12318614278. There is some confusion though as we tested this part on an early B58 and it fit so we are trying to determine the differences. What we do know is if your stock alternator pulley is held on by a 24mm nut instead of a 22mm nut then this will not fit. We are producing a version that does fit and will also fit the S58 alternator. Does not fit any car with a 48V alternator 12318490540 - also known as Mild Hybrid. We are working on a 48V version though. Installation Instructions