Other Articles - December - 2020

Get in Line! A Machinist’s Look at the 6L80/6L90 Pump Alignment

The 6L80 and 6L90 transmissions have been in the aftermarket for over a decade. By now, most transmission shops see these transmissions regularly. One common issue that brings these units to your shop is torque converter failure, which also destroys the pump. With this in mind, many shops are prepared to replace or repair the pump assembly as necessary. Since these units are so popular now, many shops have opted for the repair path for a solution. This requires a machine shop to restore the pump pocket and stator surfaces. Realizing this is a delicate process, I decided to visit my local machinist to get some tips on installing a machined pump assembly.


In order to get the details correct, I took a trip to see Mike Tilley, who owns his own machine shop (Arizona Transmission Machine Inc.) since 1988. He walked me through the details of repairing the damage that commonly occurs in the pump due to torque converter failure. I will get further into the details on a follow up article!

It was amazing to see the number of pump assemblies waiting to be repaired! Mike advised me that the 6L pumps are the most popular machining repair in his shop today. Most of them arrive at his shop as matched assemblies, however, some come as pump bodies or stators alone.

The shop is set up for one purpose; machining parts! While the shop is not a large footprint, every square inch of the operation has a definite function for this one-man operation.


Realizing that Mike used to be a transmission builder prior to becoming a machinist, I asked him about pump alignment on this unit. Mike said, “The best way to do it is the way the OEM recommends; using an alignment tool.”

Pump alignment is critical to the survival of this unit. GM recommends Kent Moore tool #J-46664 to perform this job. Mike showed me his version of this tool, which is available at www.ez-driver.com. The article in the October/ November 2020 edition of Gears magazine titled “Did You Know” shows this tool in use. Also in the article, mention of using alignment dowels was made, but is not supported by the OEM. Even though the holes referenced have a unique fit relative to the remaining bolt holes, there is enough variance in the finished diameter of these holes that cause an alignment issue. Measuring the diameter of these holes in different stators ranged from 0.247” to 0.250”. The most frequent measurement was 0.248”. The TAAT valve body bolts measure 0.246” (6.25 mm), which leaves some wiggle room.

While using these holes as a guide gets you close, the alignment tool is always the best way to ensure alignment is correct, using alignment dowels may leave you off center. Also, the assembled Arizona Transmission Machine Inc bell housing can be installed in the unit with no abnormal amount of effort, even if it is slightly off center. This can lead to premature stator bushing wear.

There is always more than one way to perform different build procedures in transmissions. As new units phase into becoming common units, the procedures and short cuts become more numerous. Always take a moment to validate your end result relative to the recommended procedure. In the end, if it works for you and you have success, use it!