How to Fix Delayed Engagement in 8L45/90 Transmission

by parker
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Delayed engagement is a common issue that can occur in transmissions, including the GM 8L45/90 transmission. In this article, we will discuss the causes of delayed engagement and how to fix it using General Motors’ recommended procedure outlined in their TSB (Technical Service Bulletin).

Understanding Delayed Engagement

Delayed engagement refers to the delay in the transmission engaging when the vehicle is shifted into gear, particularly after the vehicle has been sitting for an extended period of time. This can be frustrating for drivers and may indicate an underlying issue with the transmission.

General Motors’ TSB on Delayed Engagement

General Motors has issued a TSB addressing the problem of delayed engagement in the 8L45/90 transmission. The TSB recommends a specific correction involving the stator support. The stator support is responsible for regulating fluid flow within the transmission and is directly linked to delayed engagement in this case.

The Correction: Adding an Extra Check Ball Capsule

To address the delayed engagement issue, General Motors added an extra check ball capsule as an air bleed in the cooler out passage of the stator support. This modification allows the transmission to pump the converter full more quickly when the vehicle is started, eliminating the delay. The new design of the stator support includes this check ball capsule.

Assessing the Severity of Delayed Engagement

Before replacing the stator support, it is important to assess the severity of the delayed engagement. If the delay is minimal, it may not require a stator support replacement. It could be due to other factors such as a programming issue or a problem with a clutch pack. Replacing the stator support in these cases would not solve the problem, so it is crucial to diagnose the issue accurately.

Checking for Drain Back Issues

One way to check for drain back issues, which can contribute to delayed engagement, is by performing a simple test. Drive the vehicle and then put it on a rack for a short period of time, allowing the transmission to cool down. After a brief period, remove the rubber fill plug from the side of the transmission and insert a piece of coat hanger to check the fluid level. Leave the vehicle overnight and repeat the process in the morning. If the fluid level is significantly higher on the coat hanger in the morning, it indicates a drain back issue that needs to be addressed.

Consider Replacing the Case Cover

The TSB has been revised multiple times, and one of the revisions suggests replacing the case cover as a precautionary measure. While not explicitly required, it is a good idea to replace the case cover in case there are any potential machining issues that could affect the transmission’s performance. This step can help eliminate any lingering morning sickness or delayed engagement.


Delayed engagement can be a frustrating issue in the GM 8L45/90 transmission. However, by following General Motors’ recommended procedure outlined in their TSB, it is possible to address and fix the problem. Remember to accurately diagnose the issue before replacing the stator support and consider replacing the case cover as a precautionary measure. By following these steps, you can ensure smooth operation and eliminate delayed engagement in the transmission.

Thank you for reading, and we hope this article has been helpful in understanding how to fix delayed engagement in the 8L45/90 transmission.

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