Rough shifting Tranny

iggieSeptember 30, 2009

The transmission on my 05 Buick Lesabre started to shift rough the other day, does not slip or bang excessivelt, but where it used to be smooth and the shifts unoticed now a slight bump can be heard and felt. The Fluid and filter have been changed, this stopped the hard shifting for a few days and then it started again, Car has 90K miles and runs fine . Several have said this is nothing to be concerned about, is simply normal. Any advice or opinons will be greatly appreciated. Iggie

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john_g

The PCM learns from driver inputs (operating habits) as well as it learns to compensate for wear. If it detects some slippage from a particular clutch the PCM will attempt to correct for that by increasing the line pressure so the clutch applies quicker and harder. The trick is, sometimes the software gets it wrong and it can cause some harsh shifting when there is nothing that really needs to be compensated for. In those cases the engineers often release software updates that we can reprogram the PCM with to improve harsh shifting concerns. This would be worth having a tech check it out to be sure if it is an indication of a problem be it mechanical or software based. At the least, the tech could reset the learned adaptives and restore the original shifting characteristics.

    Bookmark   October 4, 2009 at 9:25PM
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iggie

Thanks for the post John G, however, I did not state the problem clearly, the tranny does not shift harshly 100% of the time, usually does it after being driven 40 or 50 miles and then if car sits a few minutes it will resume shifting normally. Although sometimes it starts off shifting rough and then clears up. Does not slip. the service manager at a local GM dealer advises just leaving it alone.

    Bookmark   October 7, 2009 at 2:21AM
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