Torque converter lock-up...

[Dano]

Anyone know when the TC should lock. I have an '06 SE,KC, Off-Road 4x4 and the tach and speedo seem to sync around 50 mph. The tach appears to "float" below this point. It would seem to make sense that the mpg would be a little better if the "slippage" ended at around 40 mph. Comments....?? By the way, I'm getting about 11 mpg in town/17mpg on the road. I have have 1200 miles on this ride.

[sudden urge]

Originally Posted by Dano

Anyone know when the TC should lock. I have an '06 SE,KC, Off-Road 4x4 and the tach and speedo seem to sync around 50 mph. The tach appears to "float" below this point. It would seem to make sense that the mpg would be a little better if the "slippage" ended at around 40 mph. Comments....?? By the way, I'm getting about 11 mpg in town/17mpg on the road. I have have 1200 miles on this ride.

Mine locks up at 40-45 mph if the motor and trans are at operating temperature. If it's not at operating temperature, it won't lock till after 50 mph.

[Carbeaux]

Originally Posted by Dano

Anyone know when the TC should lock. I have an '06 SE,KC, Off-Road 4x4 and the tach and speedo seem to sync around 50 mph. The tach appears to "float" below this point. It would seem to make sense that the mpg would be a little better if the "slippage" ended at around 40 mph. Comments....?? By the way, I'm getting about 11 mpg in town/17mpg on the road. I have have 1200 miles on this ride.

What you state here is pretty normal. You might be able to push that mileage to almost 18, but you better have a really light foot and drive slowly. No 85 mph highway speeds. Your TC is locking at the same point as the rest of us from what I've read.

[titan814]

this may be a dumb question but how do you know its locked up?

[pop]

Originally Posted by titan814

this may be a dumb question but how do you know its locked up?

I'm glad you asked that question. I've wondered for a long time myself.

[Mr. B]

Also, you can "feel" it when it locks up .... the motor get more of a load on it .... and with my MagnaFlo, I can hear the motor change tones...... the wishy-washy TC in our trucks is one of my only complaints ..... I'm sure there's a reason that they designed it that way .... probably to protect the tranny or something, but any slight adjustment in your speed while traveling at hiway speeds causes it to unlock and slip a little ..... our trucks also downshift much too easy ..... I look forward to somebody coming out with an aftermarket computer chip or reprogramer that will allow us to modify the TC lock-up.

[Thrust_Titan]

Vehicle Speed When Performing and Releasing Complete Lock-up.
.
At closed throttle, the accelerator opening is less than 1/8 condition.
At half throttle, the accelerator opening is 4/8 of the full opening.
.
Throttle position Vehicle speed km/h (MPH)
Lock-up “ON” Lock-up “OFF”
.
2.937
Closed throttle 74 - 82 (46 - 51) 71 - 79 (45 - 49)
Half throttle 188 - 196 (117 - 122) 136 - 144 (85 - 90)
.
3.357
Closed throttle 65 - 73 (41 - 46) 62 - 70 (39 - 44)
Half throttle 168 - 176 (105 - 110) 118 - 126 (74 - 79)
.
.
Vehicle Speed When Performing and Releasing Slip Lock-up.
.
At closed throttle, the accelerator opening is less than 1/8 condition.
.
Throttle position Gear position Vehicle speed km/h (MPH)
Slip lock-up “ON” Slip lock-up “OFF”
.
2.937 Closed throttle
4th 52 - 60 (33 - 38) 49 - 57 (31 - 36)
5th 52 - 60 (33 - 38) 49 - 57 (31 - 36)
.
3.357 Closed throttle
4th 46 - 54 (29 - 34) 43 - 51 (27 - 32)
5th 46 - 54 (29 - 34) 43 - 51 (27 - 32)

[Quad T]

Originally Posted by Mr. B

our trucks also downshift much too easy ..... I look forward to somebody coming out with an aftermarket computer chip or reprogramer that will allow us to modify the TC lock-up.

Well put!!!

There are several what I will call small hills I travel on my way into work. The road has a speed limit of 40 so I'm doing about 45. I know full well with 379 freegin foot pounds of torque there is no need to downshift because I'm very, very light on the gas pedal hoping I can get over the hill without the downshift. And yup, sure enough, just before I get to the top the silly thing downshifts only so it can upshift a few seconds later. This really drives me crazy as this is my first automatic tranny since 1986 and I am so not used to my vehicles shifting on their own.

[Dano]

...not a stupid question...a Torque Converter (TC) is nothing more than a "fluid" coupling (or clutch, if you will) between the engine and the transmission. A clutch, as on a standard transmission, allows some slippage while you're engaging the engine to the transmission. You know, when you let-out the clutch, there is slippage as the vehicle comes up-to-speed. By the time the clutch pedal is all the way out the engine and the transmission are fully engaged - there is no slippage. On the current automatic trans. vehicles, there is a "fluid coupling" (clutch) instead of a manual, foot operated clutch. Because fluid is viscous (slippery), the torque converters of the old days never could quite fully engage the engine to the transmission. In other words, there was always some "slippage" occuring. This inefficiency usually resulted in poorer gas milage and premature fluid decay (from fluid friction). Enter the "locking" TC. Without getting into a very lengthy explanation of actually how it locks, suffice it to say that through an electro-mechanical process, the TC does actually fully engage (locks-up) the engine to the transmission; thereby preventing any slippage. This usually occurs when the micro-processor (computer) senses the right perameters, i.e., road speed, engine/trans. temperature, manifold vacuum, gas/air flow, trans. gear, etc. Now, to answer your question. Unless you have a "well-tuned" ear and can here the engine RPM's drop and remain unchanged relative to accelerator pressure, you can look at the tach and speedo. According to what most are experiencing, watch your tach between 45 to 55 mph and see if it drops to a level (probably about 1500 rpm's -- this depends on the axle ratio you have) regardless of your accelerator pedal pressure. In other words, you'll know when the "lock-up" occurs because slight accelerator pedal pressure does not cause the tach to suddenly bump up to a higher rpm. Instead, the tach and the speedo will stay synchronized. Your speed will increase proportionately with the tach. Now, if you want to see the TC unlock, just press a little harder on the gas pedal and watch the tach immediately jump up a few hundred rpm's. Sorry to be so long winded. OK, so now you can get a job at Nissan fixing Torque Converters...

[pop]

I finally understand TC lockup. Maybe.

[pop]

I've been watching this tread. I am new to towing so I've been trying to figure out how to keep my TC locked (I have an 05XE and do not have the tranny guage). I do think I've got it now though.

[loufish]

According to what most are experiencing, watch your tach between 45 to 55 mph and see if it drops to a level (probably about 1500 rpm's -- this depends on the axle ratio you have) regardless of your accelerator pedal pressure.

Mine won't lock up those speeds unless I'm very light on the throttle..and when it does it will unlock at the slightest increase in throttle. My T/C seems happest over 60 mph.

Does anybody know for sure if the T/C locks up fully in third gear?

[sudden urge]

I said earlier that mine will lock up at 40 mph if it is fully warmed up. That's 1000 rpms when she locks. No big tow on mine. I find it annoying in the city, so most of the time I put it in 4 during city driving.

[loufish]

I find it annoying in the city, so most of the time I put it in 4 during city driving.

I keep mine in 4th also, the T/C will slip all day in town around 40-50 mph...