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Extending the life of a Honda converter clutch

Monday, April 28, 2014 - 07:00
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Figure 2There are three operational states for the converter clutch: fully applied, partially applied and fully released. All three states must work correctly, or the converter is in trouble.

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Fully applied — The main concern with full lockup is that there is sufficient flow to and pressure in the converter to provide sufficient clamping force to prevent clutch slippage under load. For example, an Odyssey loaded with people on the freeway pulling a long hill relies on good converter charge with sufficient pressure to prevent clutch “creep” from superheating the front cover and lockup clutch lining on the damper plate.

Partially applied — Partial lockup is less active on heavier class vehicles, but on the light stuff, like Accords and TL’s, it can be very active, especially at lower speeds, lower gears and lower rpm. Because partial lock is controlled by duty cycle applied to one of the linear solenoids, which in turn acts on the lockup control valve, the amount, or percentage of lockup can be controlled.

Concerning these first two states: When the whole vehicle is in new condition, the full and partial lock system just barely operates well enough, but as the vehicle ages, many things begin to change, such as:

• The condition and quality of the ATF drops drastically. Even with regular services, all the fluid does not get replaced unless the cooler return line is removed and you keep pouring new ATF into the trans while it runs until it pumps the old ATF out of the converter. Few do this, since they don’t want to pay for 15 quarts of new ATF, some of which will be discarded.

• Linear solenoids don’t regulate as precisely as when new because the internal springs can fade, and valves and bores wear.

• Valves and solenoids begin to stick because of particulates in the ATF.

• The pump gains clearance as it ages and expands from heat and pressure, and pump volume output and efficiency drop.

• The converter clutch lining loses holding capacity as the coefficient of friction changes.

• Overall internal hydraulic system leakage increases through varied amounts of wear here, there and everywhere. It’s not huge at any one place, as much as it is cumulative in effect.

• Resistance in old wiring and connectors rises.

• Engine performance declines with changes in cam and valve timing, as with a host of other things, and the sensor inputs used for lockup control are not at optimum. So the computer does not control the trans and regulate pressures in the same way as when everything was new.

Looking down this list, one might think, “Well, many of these things can be and are replaced when the transmission is rebuilt!” Yes, that certainly is true. But look again at the last three in the list. Transmission repair centers do not sell a new timing belt and valve adjustment with the trans rebuild to get the computer working the way it did when the vehicle was new. And these are significant factors beyond what most people realize. Now add to this some mismatch oddities among dynamic functional characteristics, and programmed operational parameters.

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