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A triple transmission threat

These transmissions can throw problems at you from several directions. You need to be ready with a good defense.
Friday, February 28, 2014 - 09:00

In the late 19th century, gridiron (grid – iron) football emerged here in North America, a deviation of both rugby and association (soccer) football. Nowadays, we simply call it football. But back in the day, in addition to playing defense, a player in the gridiron game could be referred to as a “triple-threat-man” if he excelled at kicking, running and passing. He was the team’s utility man and a big threat to the opposing team.

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What does this have to do with transmissions? Well, it’s just my own personal viewpoint of how I observe a problematic transmission. I call it a “triple-threat-trans,” for it can oppose you on any one of three fronts, or a combination thereof: mechanically, hydraulically and/or electronically.

I find by breaking the transmission down into these three basic categories contributes to the diagnostic process. The computer calls the plays; the electrical solenoids receive that command, which in turn, directs hydraulic pressure to operate mechanical parts to complete the play. Each play begins with a command based on computer programming ending with a controlled gear transition. Besides the initial command and the achieved shift, there are many things that can go wrong in between. With some causes being less thought of than others, to mention a few of these overlooked points might be helpful.   

Starting with programming (Figure 1), there can be challenges in determining a problem in this area affecting the direction one would take in the diagnostic process. At times, manufacturers might not develop the cleanest software affecting the quality of a shift and/or shift scheduling. Premature failure of the transmission occurs during the warranty period prompting reprogramming repairs. As a result, these types of failures do not regularly show up in aftermarket repair facilities.

But when it does, a transmission comes in with just 15,000 miles on it for example, yet one or two clutch assemblies are totally destroyed with no visible signs as to why. The fluid isn’t burnt, no bushing failure, sealing ring failure or rubber seal failure can be found anywhere. In fact, you stack up the assembly with new steel and friction plates and it pressure checks perfectly. Usually, at this point, the valve body and/or solenoids become suspect when all along the route cause is really a programming issue.

The opposite also is known to occur. For fuel economy purposes, a perfectly good program is written for what is commonly referred to as a “neutral idle stop.” The computer commands off the driving clutch during “in gear” idle stops, such as stopping at a red traffic light. As soon as the brake pedal is released, the computer engages the clutch before the accelerator pedal can be depressed. In time, valves in the valve body wear into the bore hydraulically compromising the task resulting in a flare-bang engagement.

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