Shift Pointers
- Author: Wayne Colonna
- Subject Matter: Vibration
- Issue: Mounts could be cause
Malfunctioning mounts are notorious for causing a wide variety of vibration complaints including what is often thought of as a converter clutch vibration, judder or shudder; particularly so with vehicles that perform cylinder deactivation for fuel economy.
The mounts used can be liquid filled that are either electrically (figures 1 and 2)
or vacuum controlled (Figure 3) to dampen the effects of an engine not running on all of its cylinders.
When these mounts soften or lose their liquid and collapse (figures 4 and 5), they transmit the cylinder deactivation through the vehicle. This of course gets misinterpreted as a converter clutch problem as deactivation occurs near the time a converter clutch may apply.
With a wide variety of car manufacturers utilizing this type of strategy, it is good to keep this in mind when fighting what is thought to be a TCC issue when it is not. What can be a tip-off that the mounts are the problem and not a torque-converter clutch issue is the shudder occurs at the same time deactivation is taking place. Some manufacturers inform the driver that deactivation is taking place by way of an indicator light. An ECO light in a Honda is one such example. This too can aid in a quicker diagnosis if one pays attention to this detail.
This does not eliminate non-liquid filled mounts as being problematic. Non-liquid filled mounts malfunctioning in vehicles that do not perform cylinder deactivation are also prone to being misdiagnosed as a converter clutch shudder. An excellent example is 2006-and-later Dodge Chargers using the NAG1 behind a Hemi in police packages. A complaint of a driveline vibration or a shudder is felt coming to a stop. But when Autostick is enabled the vibration goes away. This immediately causes one to think TCC issues because when Autostick is not enabled, the TCM provides a “partial” electronic modulated converter clutch (EMCC) strategy on the downshift. When Autostick is activated, it delays EMCC strategy and no longer partially applies the clutch on downshift. For this reason the converter clutch is blamed. But what is really happening is the bad spongy mounts are transmitting the partial EMCC strategy through the vehicle.
Although only a couple of examples were cited in this article, the idea is to remain mindful that mounts are one possibility to what may be thought of as a TCC shudder problem. It’s always good to start simple before getting overly invested in time and money chasing after the wrong cause to a problem.
