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Custom Dodge Ram Performance Mods - Engine - 5.7 HEMI V8 Discuss modifying your Dodge Ram with Performance Parts and Accessories!
Factory Spec: 5.7-liter HEMI® V8 engine - 390 horsepower, 407 lb-ft of torque.


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  #1  
Old 11-08-2011, 11:42 PM
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Default Torque Converter?

What is the difference between a locked tc and an unlocked tc? And what is a lockable tc?
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Old 11-08-2011, 11:55 PM
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All I have heard is that a locked torque converter physically links the impeller and turbine, which changes the converter into a mechanical coupling. The result is no slippage, and virtually no power loss. Most people say there isn't a whole lot of difference on the track but a big difference on a dyno. thats all i know of, hope someone else will have some more/better info.
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Old 11-09-2011, 02:22 AM
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Also how do you know if its locked or not? Or even lockable or unlockable for that matter?
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Old 11-09-2011, 11:30 AM
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Ramtex i wouldnt know too much really if or how u can find out if the tc is locked or not but i know if its locked you will recieve better performance but i wouldnt know by how much either.But i got a question for u Ram tex, did u get better performance after u installed your 90mm tb??
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Old 11-09-2011, 11:55 AM
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I'm hardly an auto tranny expert, but I did get some decent exposure to locking converters and tranny issues because of owning some GM 700-R4 equipped vehicles over the years. On the original question, I'll say that most all modern auto trannies have lockup tc's. These have almost become a requirement due to fuel economy and even a wear factor for reliability. TC's with lockup basically have some kind of clutch mechanism that engages the output from the crank to the drivetrain in a pure mechanical state rather than a hydraulic pressure or fluid drive manner. You can see that a mechanical direct coupling when that coverter is in lockup mode is going to be more efficient than the hydraulic pressure mode. It will also generate less heat in the tranny when the tc is locked up.

Now as to what causes the lockup equipped converter to engage at a given point, I think different factors can be applied depending on design. I think the most common is computer control based on rpm, load, speed, etc. Other factors can come into play of which I'm not as well versed. As far as how you know your converter is locked up or not, some vehicles used to have an indicator in the earlier days and some may still have that. However, on most vehicles today with lockup tc's that I've seen, you almost have to watch the tach to detect or know when it engages and disengages. Lockup tc's have become so common that you don't usually get any indicator for tc lockup.

Again, I'll clearly state that I'm no tranny expert, and some of what I've said does not apply to all vehicles by any means and should be considered somewhat general as it applies to our Dodge trannies.
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Old 11-09-2011, 12:11 PM
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I think just about every modern TC these days has lockup capability
it's the computer settings that control whether lockup is engaged or not.

Factory settings typically engage lockup once you reach a certain speed/rpm (usually after 3rd gear ,depending on load) to maximize fuel economy under fairly light throttle pressure.

Custom Tuning (like Diablo) can allow lockup earlier by programming the TCM tables for any gear/rpm and even under full throttle.
Even the canned Diablo tunes have advanced lock up over stock for better accelleration performance (racing) as opposed to just better fuel economy (stock)

YouTube on How a Torque Converter works, including "lockup"
(and a couple on auto transmissions)



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Old 11-09-2011, 12:13 PM
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The Lockup Torque Converter
Because the only connection between two sides of a torque converter is a fluid connection, there is always a little slippage, running from about 2-8%. To increase efficiency and gas mileage, most modern automatic transmissions also have something called a lockup clutch (aka, torque converter clutch).

It works like this. As the speed of the car nears 40 miles per hour, the highly pressurized transmission fluid is channeled through the transmission shaft and activates a clutch piston. This metal pin locks the turbine to the impeller, in effect bypassing the torque converter. It remains this way until the vehicle slows below 40 mph, at which point the clutch piston disengages and the torque converter kicks in again.

That is excerpt about automatic transmissions from a good source, it does go into more detail here
http://www.edmunds.com/car-technolog...rticleid=43836
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Old 11-09-2011, 12:42 PM
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I've always wondered how lockup was controlled/monitored. The only thing I could come up with was monitoring the crank position sensor and transmission input shaft, and basing it on variations in speed between the two, but I doubt this is correct. According to GT it has to do more with final velocity of the transmission output shaft, but I think load, rpm, etc... matters as well.
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Old 11-09-2011, 01:46 PM
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Quote:
Originally Posted by snrusnak View Post
I've always wondered how lockup was controlled/monitored. The only thing I could come up with was monitoring the crank position sensor and transmission input shaft, and basing it on variations in speed between the two, but I doubt this is correct. According to GT it has to do more with final velocity of the transmission output shaft, but I think load, rpm, etc... matters as well.
Yes, I think as vehicle computers began monitoring more and more inputs with more sensors, the shifting and converter lockup gets more sophisticated. I'm pretty sure my old '89 700-R4 had fewer shift and lockup commands from the computer than my '12 Express. There are definitely still mechanical-only aspects affecting shifting and lockup, but I'll bet a nickel the computer is the biggest factor these days. I'm new to the Dodge pickup, but I read here frequently that the 6-speed auto in my '12 is basically the same 5-speed version in the '11, and that the bulk or all of the ability to have 6-speeds is a software issue and little if any large mechanical change. It's downright scary...LOL!
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Old 11-09-2011, 01:49 PM
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Quote:
Yes, I think as vehicle computers began monitoring more and more inputs with more sensors, the shifting and converter lockup gets more sophisticated. I'm pretty sure my old '89 700-R4 had fewer shift and lockup commands from the computer than my '12 Express. There are definitely still mechanical-only aspects affecting shifting and lockup, but I'll bet a nickel the computer is the biggest factor these days. I'm new to the Dodge pickup, but I read here frequently that the 6-speed auto in my '12 is basically the same 5-speed version in the '11, and that the bulk or all of the ability to have 6-speeds is a software issue and little if any large mechanical change. It's downright scary...LOL!
If you really want to blow your mind then realize that the same "6 speed" transmission you have, that is the same "5 speed" transmission that I have, is actually the same "4 speed" transmission in the early 2000's chrylsers. Identical physically, different programming. I believe they get different gear ratios out of them by using planetary gear systems and combinations.
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