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Old 02-28-2014, 05:29 PM   #253
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Hmmm?

I don't know what that means in any useful way. I watch the tach all the time.

Maybe I would ask it this way. When I am going upgrade and holding the car in 3rd gear for miles, is the TC locked? The whole time? What would make it change states?
Depends entirely on load at the time...and it varies by make, I assume. I'll tell you how GM works though.

TC can lock in 3rd - 6th gear, but it is dependent upon load and corresponding throttle opening. TC engagement feels like a very light gear shift. You have to be sensitive to it.

On the tach you'll see about a 50 - 150 rpm rise upon disengagement (again dependent on load) and it may not be a totally smooth tach needle movement, as many TCs are not "on/off", but rather PWM. Application will show a like drop in RPM. With an 8 speed, it might be difficult to tell the difference between TC and a shift, due to the close ratios of the gears.....I've not driven one yet.
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Old 02-28-2014, 05:47 PM   #254
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Hmmm?

I don't know what that means in any useful way. I watch the tach all the time.

Maybe I would ask it this way. When I am going upgrade and holding the car in 3rd gear for miles, is the TC locked? The whole time? What would make it change states?
As far as I understand transmissions, you want the TC to be locked. It's when there's slippage that problems can occur, correct?
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Old 02-28-2014, 06:03 PM   #255
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As far as I understand transmissions, you want the TC to be locked. It's when there's slippage that problems can occur, correct?
That's my understanding. Locked generates less heat. But, it's not totally clear to me how to control it. I have been assuming that if I hold it in a low gear, like 3 or 4, it will stay locked if I am on the gas, and might unlock if I let off on the gas.
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Old 02-28-2014, 06:14 PM   #256
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With all the gears that thing has, it will probably just downshift and relock the TC. The scangage will tell you the slip. If it is less than 1 it is slipping. Slipping amplifies torgue and generates heat. Temp rise is usually a sign. All the gears are to save gas.

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Old 02-28-2014, 06:20 PM   #257
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Although this isn't technically what is actually happening, it can be useful to think of a torque converter unlocking as driving a manual transmission car and holding your foot slightly on the clutch so that the RPM's go up but the clutch isn't totally disengaged. The clutch is at that time "slipping" and heat as well as wear-and-tear dramatically increase. Although the torque converter in an automatic works nothing like this, it is a good way to THINK of how a torque converter slipping will affect RPM's and heat/slippage. A fully "out" clutch would be seen as equivalent to a locked torque converter; a "half way down" clutch would be seen as equivalent to an unlocked torque converter; slipping, but still propelling the car at higher RPM's.

Apples and oranges, but you get the idea.
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Old 02-28-2014, 07:31 PM   #258
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Totally unrelated to mstephens overheating issue.

ggoat described torque converter locking and unlocking and compared it to a manual transmission clutch. I'm NOT challenging his analogy but PLEASE PLEASE PLEASE do not use the a manual transmission clutch pedal as an attempt to increase torque, HP, passing power or anything. The only time the clutch can be used in a partial slip mode is during the initial standing start to get the vehicle in motion and maneuvering as in backing into your site. For maximum clutch life, minimize the amount of time a clutch is being slipped. This time is easiest described as the time that your foot is coming up off of the floorboard but the clutch is not yet fully engaged (foot completely off of the pedal), RPM in (from engine) is GREATER then RPM out to transmission.

Clutches create tremendous heat if only partially engaged, easily over 1000 DEG F is easily possible and very damaging to the clutch.

I claim no special knowledge of the inner workings of an automatic transmission. I do claim knowledge of automotive and pickup truck clutches, it is has been my sole profession for over 30 years.

Wishing mstephens a successful repair.

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Old 02-28-2014, 07:36 PM   #259
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Originally Posted by ggoat!!! View Post
Although this isn't technically what is actually happening, it can be useful to think of a torque converter unlocking as driving a manual transmission car and holding your foot slightly on the clutch so that the RPM's go up but the clutch isn't totally disengaged. The clutch is at that time "slipping" and heat as well as wear-and-tear dramatically increase. Although the torque converter in an automatic works nothing like this, it is a good way to THINK of how a torque converter slipping will affect RPM's and heat/slippage. A fully "out" clutch would be seen as equivalent to a locked torque converter; a "half way down" clutch would be seen as equivalent to an unlocked torque converter; slipping, but still propelling the car at higher RPM's.

Apples and oranges, but you get the idea.
Well, I see what you are trying to say, but the real problem with this comparison is it does not address the fact that when a TC is "unlocked" it is acting effectively like a lower gear, as it actually multiplies torque.
Slipping a clutch in a manual does not in itself multiply torque, although the increase in rpm would potentially ( likely ) result in more torque.

I have not driven one of these eight speed wonders either, but I am willing to bet it is going to be darn near impossible to tell when the TC is locking and unlocking with this trans. And since this design does not have a "tow mode" I doubt you have any practical tools at your disposal as a driver to control the TC lock/unlock.

EDIT: my comment about tow/haul mode is in reference to pickup truck trans like our 5R110 Ford that have that feature. Engaging tow/haul enables the TCM to alter the way the torque converter locks and unlocks, with the purpose being, as mentioned, to help keep trans oil temps lower. Tow/haul does other things also to the shift program.
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Old 02-28-2014, 08:05 PM   #260
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In 3rd gear and 3200 RPM doing 55mph, it would not seem like TC would unlock to multiply torque. That is nearing the peak torque of the engine.

This is a very interesting subject to me. Maybe there is an tech at Chrysler corp that can spell it out. if the scangauge type device indicates lock, thats a super reason to have one.
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Old 02-28-2014, 08:34 PM   #261
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not sure I understand about replacing the heads--if the problem was because of the design of the heads, and they're going to replace with the same thing...itsn't the problem just going to come back? Or do we not really know the root cause of the problem?
I've been browsing Durangos...most have the same 6, but a 5-speed trans. I wonder how different that is? The Hemi models have a 6 speed....starting 2014, they're both getting an 8. Would that be the same one you already have in the 300?
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Old 02-28-2014, 08:39 PM   #262
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The Durango also has a fairly high tow rating on that engine - over 6000lbs.
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Old 02-28-2014, 09:07 PM   #263
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Quote:
Originally Posted by GCinSC2 View Post
Totally unrelated to mstephens overheating issue.

ggoat described torque converter locking and unlocking and compared it to a manual transmission clutch. I'm NOT challenging his analogy but PLEASE PLEASE PLEASE do not use the a manual transmission clutch pedal as an attempt to increase torque, HP, passing power or anything. The only time the clutch can be used in a partial slip mode is during the initial standing start to get the vehicle in motion and maneuvering as in backing into your site. For maximum clutch life, minimize the amount of time a clutch is being slipped. This time is easiest described as the time that your foot is coming up off of the floorboard but the clutch is not yet fully engaged (foot completely off of the pedal), RPM in (from engine) is GREATER then RPM out to transmission.

Clutches create tremendous heat if only partially engaged, easily over 1000 DEG F is easily possible and very damaging to the clutch.

I claim no special knowledge of the inner workings of an automatic transmission. I do claim knowledge of automotive and pickup truck clutches, it is has been my sole profession for over 30 years.

Wishing mstephens a successful repair.

Gary
Hi Gary...

I definitely wasn't inferring that anyone should ever partially slip a clutch; I was trying to point out, as you did much more eloquently than I, that slipping a clutch was a BAD thing...and I used the inherent "badness" of slipping a clutch as an analogy to letting a torque converter constantly slip. Both generate tons of heat; both are BAD.

Thanks for clarifying,
Jeff
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Old 02-28-2014, 09:13 PM   #264
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The Durango also has a fairly high tow rating on that engine - over 6000lbs.
Which engine ? The V6 or the Hemi V8 ?
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Old 02-28-2014, 09:18 PM   #265
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The V6, the Hemi has 7200 or 7400 depending on 2wd or 4wd.

But remember, the Durango is marketed as a tow vehicle. But I digress to another towing thread.

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Which engine ? The V6 or the Hemi V8 ?
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Old 02-28-2014, 09:34 PM   #266
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A torque converter is designed to multiply torque. When the TC is locked there is no torque multiplication. A locking torque converter is there ONLY to save fuel at cruising speeds under light torque demand. You WANT torque multiplication while towing much more of the time than when solo. If heat is a concern, due to high torque demand, consult someone for the proper cooling mods.
Remember, before the early 80's there were no locking converters, and we did fine....just wasted a lot of fuel.
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