So I noticed with the 3 speed auto tranny in my 2000 TJ that when I am running down the highway and I tap the brakes with my left foot that the RPMs go up just a little almost like the transmission is disengaging. Is this what is happening? Is it doing this through an electrical contact for the brake lights or is it some type of pressure switch. I am sure someone out there knows.
12-21-2012 08:45 PM
That is the lockup torque converter disengaging. That is what 'locks' the torque converter once you're at a cruising speed so the transmission runs cooler on the highway and so the torque converter doesn't slip and cause a loss in highwy mpg.
That is also what fools some into thinking their 3-speed automatic is a 4-speed... but that 4th "gear" they think they have is really just the lockup torque converter engaging which drops the engine RPMs a tad. :)
12-21-2012 09:53 PM
Thanks Jerry. Is this a pressure switch or just a basic electrical switch? I am thinking electrical, but cannot find anything on it.
12-21-2012 10:05 PM
The torque convertor clutch is electrically controlled (via a valve body solenoid controlled by the PCM) and hydraulically operated. Engagement occurs only in third gear and is a function of speed, coolant temp and throttle position.