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Transmission TECH/TALK

Keep an eye out for 6L80/90 defective oil pumps

The complaint

After replacing the pump assembly in a 6L80/90 transmission with a new GM pump the vehicle returns with symptoms that would appear to be caused by a low fluid condition: it falls out of gear at a stop and has low line pressure. Upon further inspection the sump filter, which was also a new replacement, is found lying in the bottom of the pan.

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The cause

Figure 1.

Some new GM pump assemblies have been mis-machined as seen in Figure 1. The machining process that creates a step and smaller diameter bore for the filter pickup tube was not performed. This causes a loose fit of the filter neck in the bore even with the booted seal on it.

When purchasing a new 6L80/90 pump assembly, be certain to check the filter pickup tube bore for the step that creates the smaller diameter part of the bore as seen in Figure 2.

Figure 2.



Transmission Digest