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Discussion Starter #1
I realize that nobody here ever answers my questions about the auto tranny, but I'm game for another try.

Do we have lock-up torgue converters? What are they and how do they work?

I looked through the shop manual last night, and cannot find the phrase anywhere. My knowledge of auto trannies is next to nil.

I'm curious mainly because (and I've seen someone else mention the same thing) I notice that when highway cruising in 4th gear and the car is finally warming up about 5 minutes after starting, there comes a point when the engine suddenly drops a few hundred RPM while maintaining the same road speed, and from then on, the engine always runs at a slightly lower RPM for any given speed than it did when the engine was still cold.

I'm just curious for an explanation of what's happening when the engine decides to drop its RPM like that.
 

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Andrew,
I don't know anything about Mitsu Automatics, but I do know a quick way for you to tell if you have a lock up converter. Get cruising at around a steady 60mph (when it is in high gear) and lightly touch your brake pedal for a second. If the car shifts down(increases revs) you have an electronic lock up since it is designed to unlock when you hit the brakes.
Hope this helps,
Steve
 

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Yes we do have a lock-up torque converter. I know since mine has been rebuilt twice already. I will find out more about them the next time I go to get my tranny adjusted since it was just rebuilt. I should have an answer by next week if I can find someone to put in my new water pump for me since I am a little under the weather right now.

Have fun driving,
Hans
 
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Yes, you do have a lockup converter. The converter has a clutch inside that activates when you reach a certain speed which causes the tranny to act like a manual transmission having direct drive. This increases fuel economy and decreases tranny temp. A torque converter is an assembly that has two turbines inside it, one is driven by the engine, fluid is between the two and the force of friction of the fluid between the surfaces is what causes a force to be transmitted to the transmission and finally to the wheels. The lockup clutch locks both halves of the converter so that they are moving at the same speed when you are on the highway. I know that this is an over-simplified explanation but that is basically how it works. This concept is why people buy higher stall converters for their cars. The higher stall allows the car to rev up higher into the powerband before the force of the fluid between the turbines reaches a sufficient level to prevent the car from revving higher without allowing the rear wheels to rotate. This higher launch RPM gives you more pull out of the hole because your car is making more torque at the higher RPM. Hope that this helps.
 

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Discussion Starter #5
Yes it does. But not completely.

> The converter has a clutch inside...

(1) And this clutch makes a physical connection, engine metal to tranny metal (or whatever material it is), as opposed to metal-fluid-metal?

(2) Is my engine dropping its RPM when (or, more properly, because) it is engaging the lock-up converter?

(3) Why does having the engine driving a metal-metal connection allow a lower RPM to keep the same MPH compared to a metal-fluid-metal connection?

(4) On our cars in particular, what conditions cause the lock-up to engage? (vehicle speed, time since startup, engine or tranny temperature, engine RPM ...)

(5) What conditions cause the lock-up to disengage? (ditto)

(6) Does this apply to all gears, or just 4th?

(4) and (5) really mean "what can I do to cause it to engage sooner, that I might get better MPG".
 
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Hi Andrew, I enjoy your posts! Here is your answer. I just bought my SL a month ago and the dealer game a 30 day warranty. After driving for a couple days I noticed all sorts of bumping in and out of gears going on. I took it to a reputable transmission shop and lucked out and found someone who actually knows the insides of our trannies. I will skip all the technical jargon and cut right to the chase. Our trannies are 4 speeds, not 3 speeds. The overdrive is the 4th speed and should be used MOST OF THE TIME. By not using it, the transmission will run hotter. (Thats what kills them). We DO have "lockup" torque converters and basically provide a mechanical linkage rather than a fluid linkage to the drivetrain,(the fluid linkage has been explained in this post earlier and is never 100% efficient. There is always some "slip" happening) and it happens IN EVERY GEAR if you let it. (If you feel really close, you actually have 8 speeds in your tranny!) The "lockup" happens when you are maintaining speed or decelerating. To get the best mileage, just be light on the throttle, keep it in ECONOMY mode and keep the overdrive ON.
Although, I must admit, I've done some experimation with mine...fast, slow, heavy foot, light foot, econ mode, power mode, etc, etc...I get 20mpg no matter what!
Anyway, the "bumping" in and out of gear is the lockup that you are feeling and is quite normal.
Another thing that the guy at the transmission shop told me is that if you want this particular transmission to REALLY last a long time, change the fluid annually instead of every 60,000 miles or whatever the book says. Hope this helps, I'm no pro but thats what I know so far!
Randy
 

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I'm not a tranny god, and this isn't specific to 3SIs, but generically speaking...


> The converter has a clutch inside...

(1) And this clutch makes a physical
connection, engine metal to tranny metal
(or whatever material it is), as opposed to metal-fluid-metal?

Yes.

(2) Is my engine dropping its RPM when (or, more properly, because) it is engaging the lock-up converter?

Not exactly.... see below

(3) Why does having the engine driving a metal-metal connection allow a lower
RPM to keep the same MPH compared to a metal-fluid-metal connection?

The whole idea of the torque converter is to replace the clutch in a manual tranny with a "fluid clutch" or Viscous Coupling that will allow a bit of slip when changing gears or sitting still, since there's no clutch to push at the proper time, and this is a lot easier than any kind of system of pulleys and such to "automatically" work a manual clutch. Because they're designed to slip though they are not all that efficient. Some of the torque from the engine will be lost as the driven side will always be turning slower than the driving side, and the engine must run faster (at any given speed) to make up for the slippage. When the lock-up engages the slipping stops, and the full load of the car is transferred to the engine causing it to rev slower, kind of like the added load of the AC slows the engine down when you turn it on.

(4) On our cars in particular, what conditions cause the lock-up to engage?
(vehicle speed, time since startup, engine or tranny temperature, engine RPM...)

In the old daze, when all this was strictly mechanical, the lockup was triggered by a centrifical clutch in the torque converter and would engage by engine speed in top gear only. Now-a-daze they are controlled by the transmission computer. I'm not sure exactly what drives it now but the computer looks at things like throttle position, brakes (on or off), engine speed, and MPH.

(5) What conditions cause the lock-up to disengage? (ditto)

(6) Does this apply to all gears, or just 4th?

Usually just 4th, because you still need the slippage to shift up to 4th.

(4) and (5) really mean "what can I do to cause it to engage sooner, that I
might get better MPG".

Just the stuff you already know. Smooth steady acceleration, get to 4th ASAP, don't jam the brakes unless you need to, ect.
 

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In my vette, the 1990 700r4, with TCC (torque convertor control-lockup), when the convertor locks up, engine rpms drop at a given speed by a couple of hundred rpm, due to the decreased slippage. I only know of this feature working in final drive/od - OEM. I do know of guys with this transmission who have incorporated a simple ground loop switch to manually lock up the TCC, for racing purposes. The effects of this are disputed, as some argue that this is extremely abusive to the transmission internals. Others use it happily. Lock up on these trannies are typically controlled by the main ECM, older models can be controlled by vacuum, and other variables.

[This message has been edited by Diablo (edited December 29, 1999).]
 

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Discussion Starter #9
I got a good answer via email from someone who, while not explicitly requesting anonymity, shall be so granted it.

Although, gimme a kiss and I might tell.

***************************

1) The connection takes place inside the converter. The clutch, located on the back of the turbine (the driven member) is forced into contact with the cover of the converter. The clutch face that contacts the cover has friction material on it and the area is contacts is machined. The answer about the impeller and the turbine locking together was not entirely accurate, although that is in effect what happens.

2) Yes.

3) Before the converter locks up, there is slippage because it is a fluid connection. The engine is turning at a slightly higher speed than the input shaft. When the converter locks up, the engine and input shaft are effectively locked together 1:1, thereby reducing engine RPM. MPH doesn't change, engine speed does.

4) Engine temperature, vehicle speed, and steady throttle position.

5) Vehicle speed, acceleration, deceleration, braking.

6) 3rd and 4th.

7) Not much, except maybe getting the car up to operating temp. before getting on the freeway and keeping your foot fairly steady on the throttle when possible to prevent it from continuously engaging and disengaging.

Try this web page for a basic explanation of lock-up converters. Look around it to find some good information on automatics in general. http://www.thegrid.net/thedrivetrainpa e/tcc.htm and http://www.thegrid.net/thedrivetrainpa e/lockup.htm. The second one has a simple animation as a visual aid that works quite well.
 
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