What is the algorithm of torque converter lock up? Does it only lock up in the 5th gear? Does it lock up in lower gears? What about soft/medium/hard acceleration?

 

Maybe dependent on year. But for some it appears to do lockups based on speed and gear selection. Seems to be at least 4th and 5th with some 3rd gear involvement.

 

This is from the 07 manual (I added the mph values since it would not copy and paste):

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TORQUE CONVERTER CLUTCH SOLENOID VALVE

'• The torque converter clutch solenoid valve is activated, with the gear in D3, D4, D5, M3, M4 and M5 by the
TCM in response to signals sent from the vehicle speed sensor and accelerator pedal position sensor (throttle
position sensor). Torque converter clutch piston operation will then be controlled.

• Lock-up operation, however, is prohibited when A/T fluid temperature is too low.

• When the accelerator pedal is depressed (less than 1.0/8) in lock-up condition, the engine speed should not
change abruptly. If there is a big jump in engine speed, there is no lock-up.

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and

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Vehicle Speed at Which Lock-up Occurs/Releases

Lock-up - Closed Throttle 31-36 mph

Lock-up - Half Throttle 86-91 mph

Released - Closed Throttle 29-34 mph

Released - Half Throttle 65-70 mph

• At closed throttle, the accelerator opening is less than 1/8 condition. (Closed throttle position signal OFF)
• At half throttle, the accelerator opening is 4/8 of the full opening.

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Again this is for an 07 and is somewhat hard to follow.

 

Thanks a lot, pfarmer! It is not easy to follow, indeed... It looks like they put incomplete information in the manual.

I was hoping to understand what happens in MM when you go from 2nd into 3rd under more than half throttle. This is when transmission sends a jolt through the whole car when it engages the 3rd gear. I thought it could be the result of TC lock-up at the time of engaging and imprecise rev-match. My thinking was that if it happens without a lock-up it should not be as harsh.

 

The TC also has a "slip-lock" function. It removes much of that annoying driveline thud you feel when the converter locks/unlocks and is much the reason why so many report that their TC never locks up. Additionally, the slip-lock function can allow partial slip and lock, dependant upon throttle and load. This can improve both efficency and acceleration.

 

The other day I was taking off on a dry concrete and when I shifted into 3rd going about 50mph, I felt the usual jolt or thud and the "SLIP" light came on for a second. I think this is only possible if TC locked up immediately after the gear change while the engine speed was higher than what's needed at this vehicle velocity and 3rd gear.

Does this make sense?

 

EDIT: TC only locks up in 4th and 5th gears. I just read that in the manual, but I don't remember at which speeds for each gear.


Get the Transgo shiftkit and you'll feel the transmission a lot more