What should be done if the companion flange nut is tightened too much when setting "crush" in a differential rebuild?

In a differential rebuild, setting the "crush" on the collapsible spacer is crucial for ensuring proper bearing preload and function. If the companion flange nut is tightened excessively, it can lead to over-compression of the collapsible spacer, which could permanently deform it and result in improper alignment or function of the differential.

Replacing the flange is appropriate when the nut has been overtightened. This is because, once damage occurs, simply backing off the nut or adjusting the cap would not resolve the underlying issue, as the spacer may already be compromised and unable to provide the correct preload characteristics. A new flange would help restore the correct relationship between the components, ensuring the differential operates smoothly and effectively.

In contrast, backing off the flange nut or loosening the cap adjusters would not rectify the problem caused by overtightening. They might adjust tension, but they wouldn't correct the damage already done to the assembly. Similarly, replacing just the collapsible spacer alone without addressing the flange could lead to continued issues, as the flange may still not seat correctly. Thus, the most effective solution in this scenario is to replace the flange to ensure the proper setup can be achieved without further complications.