Is it Necessary to Align the Bellhousing for a Transmission Swap?

Q: I’m installing a new 5-speed transmission and bellhousing in my 1993 Mustang. A friend of mine asked me whether I aligned the bellhousing. All of my parts are new, so is it actually necessary to align the bellhousing?

Yes—Bellhousing Alignment is Essential

A: Bellhousing alignment is essential for proper clutch function and making sure all related components are working properly.

Aligning the bellhousing is simply getting the transmission input shaft centerline and engine crankshaft centerline in perfect alignment with each other. The manufacturing tolerances of engine blocks and bellhousings can vary. Misaligned input shaft/crank centerlines cause the following problems:

  • Hard shifting
  • Pilot bearing wear
  • Transmission main shaft bearing wear
  • Clutch disc hub failure
  • Loss of horsepower to the wheels

Engine machine work, such as the line bore or hone can also affect alignment.

Determine Bellhousing Alignment in 3 Steps

To determine whether the transmission input shaft and engine crank fall within allowable specifications, follow this procedure:

1. Install the flywheel (only) on the assembled engine, then install the bellhousing on the back of our engine using your existing factory bellhousing dowel pins.

2. Attach your dial indicator to your flywheel and adjust the plunger until it’s in contact with the register bore of the housing. It doesn’t matter where you start.

3. Rotate the engine, noting the dial-indicator reader. Misalignment is one half of the indicator reading with a .005-inch maximum runout allowance. If runout exceeds .005 inch, you’ll need to install offset alignment bushings.

The good people at Lakewood assembled this offset dowel sizing chart to help you order the correct offset dowel pins you’ll need to achieve proper bellhousing alignment. All Lakewood dowel pins come with detailed instructions on how to achieve perfect alignment.

Total Indicator ReadingOne-Half Total Indicator ReadingDowel Size to UseLakewood Offset Dowel Pt.# GM .625″Lakewood Offset Dowel Pt.# Ford/Mopar .500″

For steel bellhousing applications that are routinely removed for clutch service, Lakewood offers fixed weld-on dowel pin kits for GM and for Mopar/Ford. These pins permanently locate the bellhousing to prevent the need for realigning it every time it’s removed.

transmission being raised up into a tunnel
(Image/Travis Jones)
Author: Dave Matthews

Dave Matthews was a mechanic for the U.S. Army, a Ford dealership, and served for many years as a fleet mechanic for construction companies. Now a technical content producer at Summit Racing, Dave has spent decades working on everything from military vehicles to high performance race machines.