Torque converter lockup/unlock question

exit395 · 05-22-2005, 07:32 PM

We took a trip to the beach this weekend towing our 4000lb trailer. I kept tranny in 4th and had tow mode on the whole trip. I was under the impression that in 4th gear that the torque converter would stay unlocked but it seems that when I would come to a hill, the engine would start to bog down then finally the rpm's would raise about 500 and I could start maintaining speed again. At one point coming home, the transmission was hunting in and out of lockup and the transmission temp gage came up significantly. I downshifted to 3rd to see if it had actually downshifted into 3rd by it's self but it was still in 4th gear. So, I guess what I'm asking is if it is normal for the torque converter to lock/unlock while in 4th gear. By the way, I discovered that you have to be in 5th gear to engage tow haul mode. While experiencing the lock/unlock situation, I took it out of tow haul mode to see if it had any effect. It would not lite up the button again until I put transmission into 5th gear.
I did a search on torque converter lock up and basically heard not to tow in 5th gear because your torque converter will lock/unlock too much causing overheating. Does anybody have the difinitive answer as to 4th gear and locking/unlocking? Thanks guys.

**loufish** · 05-23-2005, 08:50 AM

The trans will converter will unlock while in 4th gear, but it will take more throttle then in 5th to do so. If I'm running up a hill in 4th and the converter unlocks, and I'm near the top. I'll let the converter do its thing, but if the hill is long, or it's a headwind, then I'll drop it down to 3rd, and let the converter lock back up. I was a little bummed to have to shift all the way down to 3rd sometimes, then I remembered it's a 5 speed, so it will shift more often then a 4 speed....Duh!

Austin · 05-26-2005, 11:35 PM

This chart will help you:

travism · 05-27-2005, 05:46 AM

I think loufish gave a good answer that it will lock/unlock more frequently in overdrive than 4th. Although I am constantly confused on if we want the torque converter locked or unlocked. Some people say that in forth gear the converter will stay unlocked, others say it's locked in 4th. I just know the locking/unlocking frequently is not good. I've always thought that having it locked was the way to keep the tranny temp down.

The only other thing I'll add is that the tow mode only engaging in 5th is only for the column shifter I believe. Those with the console shifter can engage tow mode in any gear. I don't know why, but it makes me happier that I went with the console.
Edit: Check this thread from post #27 on for discussion about the column shifter/console shifter differences.
Towing

PrerunnerGreg · 06-02-2005, 08:05 AM

Since I got schooled on my last tranny posts, ill be sure to post good info this time. The tranny will only lock up the converter in the "final" gear selected. Only 5th if you select 5th only 4th if you select 4th. The convertor wont lock thrid though if you select 3rd. And wont lock in 4th if you selct 5th. Also, i tow alot and never use the tow mode, you can see from the charts that is bearly makes a diffence in shift points and only at 1/2 throttle. If the truck sounds like its working too hard, throw it down a gear and/or slow down.

Justintoxicated · 06-02-2005, 09:43 AM

Wait so on the console shifter tow mode only works in 5th but your not supposed to tow in 5th? Who is making this **** uP?

Austin · 06-02-2005, 09:57 AM

Quote:

Originally Posted by Justintoxicated

Wait so on the console shifter tow mode only works in 5th but your not supposed to tow in 5th? Who is making this **** uP?

Where in the world did you read that?

Tow mode changes the shift points from 1->2, 2->3, 3->4 at less than full throttle operation. That's all tow mode does. Tow mode works if you have 2nd, 3rd, 4th gear or D selected.

travism · 06-02-2005, 09:58 AM

Tow mode works in all gears. On the column shifter, it was said that you can only engage tow mode when it is in D, but then you can shift into any gear after that. I can't confirm since I have the console shifter.

ptgarcia · 06-02-2005, 05:50 PM

Quote:

Originally Posted by travism

Tow mode works in all gears. On the column shifter, it was said that you can only engage tow mode when it is in D, but then you can shift into any gear after that. I can't confirm since I have the console shifter.

This statement is correct. I have the column shifter and this is how it works on my truck.

**loufish** · 06-02-2005, 10:01 PM

Maybe I'm a little confused, I hit a button located under the radio marked "Tow Mode", I do this before I pull out of park, and can feel the shift points raised....why does it matter if I have a column, or console shifter?

travism · 06-03-2005, 04:57 AM

Sounds like you have the console/captains chairs then. I don't know why it works differently between the two shifters, it just does. Doesn't the column shifter have a manual upshift/downshift switch on it or something? Maybe it has to do with that interface.

ptgarcia · 06-03-2005, 08:18 AM

Quote:

Originally Posted by travism

Doesn't the column shifter have a manual upshift/downshift switch on it or something? Maybe it has to do with that interface.

Yeah, the column shifter has a button on the end that locks out the 5th gear (its labeled "manual shift" or something like that). In order to use the Tow Mode, you have to depress the Tow Mode switch BEFORE pressing the 5th gear lockout (manual shift) button. Otherwise, Tow Mode will not engage.

Once you press the "manual shift" button you use a paddle-like switch on the end of the column to manually go through the gears.

SickWhip · 06-03-2005, 08:25 AM

I have the Floor shifter and it just has different gates to shift from 1st-4th. There is no button to push.

electricjohn · 07-12-2006, 11:43 AM

The ECM looks at speed, vacumm, engine temp, and throttle position to detemine when to activate the torque converter clutch. On my last chevy the TCC would activate in 2nd,3rd,or 4th gear as long as I was doing 45 mph. With the nissan, I don't know about the final gear thing you are talking about.

StuntDriver06 · 07-12-2006, 01:05 PM

yeah TC wont lock until tranny is in gear you select with shifter... and takes a bit to lock in 4th... and wont lock under 4th... it would be best to have TC locked all the time for tranny heat, TC creates heat as a by-product of the slippage it allows... going in and out of locked would create lots of excess heat in the titan because the TC goes "half-locked" before it goes to full lock... the dodge i had would lock TC in 3rd 4th and all the time in tow mode but wouldnt allow 5th (4th and 5th were both OD)