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Discussion Starter #1
Just wondering if anyone know if the torque convertor locks up in third. I have a no fear titan that came with 2.94 gears and 35" tires. The wife and I bought a travel trailer which weighs 5500 loaded. I noticed tha truck likes 3rd gear (2800) at 55mph than 4th gear(2100) at 55mph, i just do not want to heat up the tranny. Thanks
 

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No it doesn't lock up in third...BUT it works out alright because the gear ratio has dropped enough that the torque load isn't too excessive and the rpm is higher resulting in more fluid flow thru the trans fluid cooling system....
 
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It can lock in 3rd. At least on my 08 it does. You have to keep an eye on the tach. You can see when it locks in 3rd and also when it breaks free and starts to slip, thats when you need to slow down or down shift and if you do not, the trans temp gauge will start to move. You should not have to much trouble with that weight.
 

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Discussion Starter #5
interesting, I will look closer next time, just seems like when I tow at 55 (CA limit) in 4th that the convertor is locking and unlocking a lot.
 

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I was just watching the tcc solenoid the other day with a scan tool. The tcc does not lock in 3rd gear.
 

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From the 2007 Service Manual:

The torque converter clutch solenoid valve is activated, with the gear in D4 , D5 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 1/8) 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.
I don't know much about Automatic Transmission internal operations. I can find stuff in the manual but I don't always know how useful or relevant it is.
 

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I'm going through a process right now of teaching myself about automatics. Doing it for free on the Internet is difficult, and I don't even have a garage yet, let alone something to tear apart.
I will say this, whoever designed the first automatics, they were geniuses.
 

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From the 2007 Service Manual:



I don't know much about Automatic Transmission internal operations. I can find stuff in the manual but I don't always know how useful or relevant it is.
I can assure that it locks in 3rd. At least on my 08 it does, also the programming Nissan does
changes from year to year, maybe some other years do not lock up in 3rd. Alot of this early lock up is also for mpg ratinigs. When towing my trailer say up a hill in 3rd locked up, the trans temp stays normal, as soon as it unlocks the gauge starts climbing. Same thing in 4th gear, best way to fry your trans is tow with it slipping, avoid that all cost unless its for a very short period of time.
 

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I'm pretty sure I've seen the same behavior in 4th. Possibly in 3rd. There are times I wish I had a manual transmission.

If what I found and what you're saying is true then the rule of thumb to tow in 4th isn't much better than towing in 5th. At least that's my take on it.
 

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Discussion Starter #11
now I'm completely confused! My truck is an 06, any idea regarding this model years programming? As I do not have a trans temp gauge I hate to guess! Thanks
 

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I still don't believe it, sorry.
 

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I'm pretty sure I've seen the same behavior in 4th. Possibly in 3rd. There are times I wish I had a manual transmission.

If what I found and what you're saying is true then the rule of thumb to tow in 4th isn't much better than towing in 5th. At least that's my take on it.
Of course 4th is better. 5th gear is an overdrive gear. Not ever a good idea to tow in an overdrive gear.
 

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Right. 4th is better than 5th, no doubt. But if the torque converter unlocks in 4th then your transmission temperatures will shoot up.
 

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4th gear is a 1:1 ratio in the re5r05a. Your trans output is spinning at engine speed when the TC is locked.
With a 2.94 axle and 35 inch tires you should probably never use 5th gear at any speed with any cargo or lack thereof.
 

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Never tow in 5th. The simple way to do this is to watch the tach, it will tell you what is going on, try this, when towing up hill put it in 3rd and use a steady pedal, dont try this with a heavy load. Try a steady speed with rpms about 2k, then push on the gas, not hard or it will downshift, it will break free of lock up and start to slip. It does the same in 4th. I always change my fluid at 30k completely or partial at 15k. I tow heavy, much easier to see all this with a heavy load.
 

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I drive over a lot of mountain passes with steep grades. There have been times going up these passes that even in third my transmission temperatures won't come down. Shifting to second gear takes care of that. I've seen this happen towing and not towing. Only once have I had to pull off and let things cool down. That was when I got stuck behind a slowpoke.
 

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Never tow in 5th. The simple way to do this is to watch the tach, it will tell you what is going on, try this, when towing up hill put it in 3rd and use a steady pedal, dont try this with a heavy load. Try a steady speed with rpms about 2k, then push on the gas, not hard or it will downshift, it will break free of lock up and start to slip. It does the same in 4th. I always change my fluid at 30k completely or partial at 15k. I tow heavy, much easier to see all this with a heavy load.
I'll be looking at it tonight in the FSM for 2008. I've been thoroughly reading the 2007 FSM already. If you're right I'll gladly accept it with a smile on my face....knowledge is power.

Until then, I have to ask....Do you have a scanner that reads transmission? Can you watch exactly what the TC clutch is doing and when it's doing it?
 

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Just for kicks and giggles, today I tried to get my TQ converter to lock in 3rd. Couldn't seem to get it to do so. 2006 BT 2WD.
 
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