With this month’s issue of POWERTRAIN PRO focusing in on reprogramming on-board computer systems, it’s good to be aware of the manufacturers increased use of this procedure with which to manage warranty issues. And at times fix or enhance the actual written program inside these modules. To search out OE bulletins to inform you of a problem that is resolved by programming is nothing short of helpful.
But then there is a whole other dimension, or should I say, let’s swing the pendulum to the other side. How about a bulletin that describes a problem that isn’t a problem? In other words, you took in a vehicle with a legitimate customer complaint thinking you are going to fix it. And you do everything you can to fix it but you never do. Only to discover the problem is inherent to the design and is considered to be operating correctly.
Such is the case with GM’s bulletin 01-07-30-042G dated Sept. 22, 2011. Their 2012 and earlier 4L60/65/70-E transmissions used in passenger cars and light duty trucks experiences a 2-3 up-shift or 3-2 downshift clunk noise. They describe the cause as follows:
During a 2-3 up-shift, the 2-4 band is released and the 3-4 clutch is applied. The timing of this shift can cause a momentary torque reversal of the output shaft that results in a clunk noise. This same torque reversal can also occur on a 3-2 downshift when the 3-4 clutch is released and the 2-4 band applied. This condition may be worse on a 4-wheel drive vehicle due to the additional tolerances in the transfer case.
The fix: This is a normal condition. No repairs should be attempted.
Perhaps this bulletin/newsletter needs to be posted on the wall as a reminder. You cannot fix what isn’t broken.
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