If you’ve ever rebuilt a manual transmission, chances are that the rebuild kit came with an input shaft bearing. On the tried-and-true Chrysler A833 four-speed, it was a run-of-the-mill roller bearing. However, if you were to tear in to a more modern gearbox, that might not be the case. The stick shift specialists at American Powertrain (AP) are well aware of this critical component and what effects it can have on transmission performance, especially if the bellhousing to crankshaft centerline alignment is off.

“Newer transmissions like all the TREMECs use a taper bearing on their input shaft,” AP explains. Since taper bearings work best when they are evenly loaded against the bearing race, proper alignment is a key element of this bearing’s lifespan. “If you don’t indicate your bell when you’re installing a TREMEC transmission, your warranty is void. That’s because we know that if your bellhousing is not centered, it’s going to ruin this input shaft bearing.”

Dial indicating the bellhousing is a simple process as long as AP’s detailed instructions are followed. Generally, all that’s needed is a magnetic base indicator, the flywheel, and the bellhousing. With these parts installed, it’s just a matter of turning the crankshaft and working some simple math to make the proper adjustments for centering. Sometimes, offset dowel pins are necessary to get it within the specified tolerance of five thousandths of an inch. “Once you’re done, your bellhousing will be centered forever and your transmission will have good, long service without any problems.”