In any language, "the point of no return," comes through loud and clear for most of us, although the mental images it inspires may differ greatly. You might picture standing up to a bully, or stepping out into your first sky dive, or simply firing up your cutting torch. Regardless of the image, regardless of the language, one thing is clear. There is no going back.
Now that you have this serious mental image in your mind, use it to avoid making a simple mistake. No going back can be the same as not being able to back up. Sure, having no reverse is not as serious as the possible consequences involved with the mental images above, but do you really want to have to tear back into a transmission because of a simple and easily avoidable mistake?
2004 and later 4F50N or AX4N units have a new design for the gasket between case and case cover. Changes in the Neutral/Reverse accumulator area required a small change in the opening for the accumulator. The 1.490" diameter opening previously used on 2000- 2003 units was increased to 1.810" in 2004.
Although the difference is quite noticeable when the two gasket options are shown side by side, it is not easy to spot when you grab one gasket and drop it onto the case. If a 2004 gasket is installed on a 2003 or earlier unit, it will create a slip in reverse or no reverse at all.
Next time you go to install that gasket on one of these units, make sure you are not reaching that "point de non-retour".
Serge Martin is Technical Director of Matech BTA Inc., Quebec and a member of the Sonnax TASC Force® (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax technicians.
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