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Extending the life of a Honda converter clutch

Monday, April 28, 2014 - 07:00
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Programmed operational parameters

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Here is where this whole scenario gets real interesting. While doing research on these transmissions, we road-tested several Acura 3.2TLs with pressure gauges attached to line pressure and cooler line, and also a gpm flow meter on the cooler. We discovered that there are times when, at low rpm in third gear between 32 and 34 mph, the computer will command LOCKUP ON (often with PARTIAL lock activated). Yet unfortunately for the transmission, the low pump speed (at about 950 rpm) was insufficient to make 125 psi. We were in traffic, low speed cruise, with only 110 to 115 psi on the pressure gauge. This meant that the PR valve was closed, and converter feed was cut off. This was not a good situation. With lockup commanded ON, but converter feed shut OFF (insufficient pressure/flow to the converter), the only thing holding the damper plate against the front cover is the centrifugal weight of the ATF as the converter spins.

But when we would toe into the gas pedal ever so lightly (so as not to kick off lockup electronically), we could get the converter to slip until finally released. When we observed this, it became all too clear why these TLs and several other models suffer repeat converter failure: It was the result of discord between the dynamic functional capabilities of the system, and the programmed operational parameters. The OE system was no longer adequate. New technology had to be created to bridge this gap.

Fortunately for transmission rebuilders everywhere, I was able to reengineer the whole PR system, and our new Sure-Cool® PR valve (patent-pending) extends the range of active converter feed down to 95 psi so that any time lockup is commanded on, the converter receives a steady and reliable supply of charge. But now this brings us to the third operational state:

Fully released — One might think, “That’s easy enough. Lockup is off. That’s no work at all!” But such is not the case. Interestingly, one of the times the lockup clutch can take a hit is when stopped at a traffic light in D. Remember that when these things get real hot, and idling in D at a stoplight, line can drop as low as 65 psi. Of course at this point, even the Sure-Cool PR valve must be closed. Yet there is a special built-in metering system to provide as much converter feed as possible without adversely affecting hot idle pressures.

Of course, if one were to steal too much flow from the mainline, the pressure could drop out the bottom and engagements can suffer. Therefore, there is a lower limit beyond which we cannot go. But as in the above scenarios, this is where some other dynamics come into play. Here is why:

Any time lockup is commanded OFF, there must be sufficient converter charge to the cover side of the damper plate. Typically in non-lockup mode (and this applies to all lockup transmissions), fluid is directed down the input shaft and delivered in front of the damper, where it flows between the cover and clutch lining to hold the clutch released. Pressure on the release (front) side must always be greater than on the apply (rear) side, for if it is equalized, rear side fluid can centrifugally drag the clutch on the cover. You don’t have to be a trans rebuilder to understand that this would not be good. It would be much like sitting at a stoplight with a manual shift trans and letting up on the clutch pedal just enough to start to drag the disc.

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