05 Impala transmission?

Can anyone explain to me the transmission in my '05 Impala? It's a base model with the 3400. Transmission just feels odd... there's four gear positions on the shifter but I feel four shifts up then if I'm on
the highway and apply really light throttle it kind of slowly drops the engine RPM way down, like there's either a 5th gear or else the torque converter is real loose and I'm feeling the lockup. Which is it? I assume the latter but don't have any experience with GM's any newer than my dad's '73 Chevy pickup.
Also, I assume that this is good for fuel economy but it is practically impossible to maintain this highest gear ratio as as soon as I have to lift off the gas for traffic etc. or have to accelerate with more than a feather touch on the accelerator it "unlocks" (or shifts down) and RPMs go way up again. Any trick to keep it locked into the top ratio? I can't imagine this constant shifting is any good for the tranny either. Would a synthetic fluid be a good idea, if I can't change the operation of it?
thanks,
nate
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That's the torque converter.
"The converter is designed to provide torque multiplication during acceleration and at slow vehicle speed, and lock-up during normal operation for increase operating economy."
Steve

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www.howstuffworks.com says:
In addition to the very important job of allowing your car come to a complete stop without stalling the engine, the torque converter actually gives your car more torque when you accelerate out of a stop. Modern torque converters can multiply the torque of the engine by two to three times. This effect only happens when the engine is turning much faster than the transmission.
At higher speeds, the transmission catches up to the engine, eventually moving at almost the same speed. Ideally, though, the transmission would move at exactly the same speed as the engine, because this difference in speed wastes power. This is part of the reason why cars with automatic transmissions get worse gas mileage than cars with manual transmissions.
To counter this effect, some cars have a torque converter with a lockup clutch. When the two halves of the torque converter get up to speed, this clutch locks them together, eliminating the slippage and improving efficiency.
Steve

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really? feels odd to me, the engine drops in pitch by a fifth or more meaning there's a significant drop in engine RPM. Also kind of oozes into lockup, feels like there's a lot of slippage (potential wear) going on there. Is this how other people's cars operate as well?
nate
(can you tell I don't usually drive automatics?)
Steve Mackie wrote:

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If you had a tach you could see. My car has the 4T60-E, essentially the same as your 4T65-E, and it'll usually drop about 250 rpm at highway speeds. If you hook a scan tool to your car, you can see the "TCC Slip Speed" which is the difference between engine crankshaft speed and torque converter turbine speed.
It's completely normal for the TCC for take 1 to 5 seconds to apply. My 4T60-E is now 10 years old and has 250,000kms on it, with no noticable TCC shudder or slipping of any kind. However, if you feel there is something wrong with your transaxle, go to the dealer and test drive another one and see if it does the same thing.
Steve

the
practically
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Also.... next time you are criusing down the highway, lightly tap the brake pedal while maintaining accelerator position, you should feel the TCC release (engine RPM increase), and then a few seconds later apply (RPM decrease).
Steve

the
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It releases almost instantly on brake application, full release of the throttle, or depression of the throttle past "a hair..." also the change in RPM is really dramatic, like I said the engine note drops at least a fifth or more so since an octave would be 50% of the initial RPM I guess this would be something like 70% or less of the initial RPM? The engine really feels like it's on the verge of lugging although I'm used to driving 4-bangers or alternately older V-8s so I might be mis-estimating. I guess I just don't see how the converter could be this "loose," I have not driven a car with such a dramatic difference between lockup and unlocked, not even my old '56 Golden Hawk which in the shop manual considered the two states to be different ratios.
nate
Steve Mackie wrote:

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N8N wrote:

Part of how GM gets segment leading fuel economy with relatively simple mechanicals is because of all of the controlled tricker going on in both engine and transmission management.
Drive another example to make sure yours isn't doing anything it shouldn't. That said, everything you have described sounds normal.
John
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N8N wrote:

Sounds exactly the way the transmission behaves in our '02 Oldsmobile Minivan. 60k+ miles and no sign of transmission trouble yet.
BTW, don't believe GM's claims for extraordinary transmission fluid change intervals. Our smelled quite bad and was turning brown by 30,000 miles, well before the manual says to change it. Go with a 2 year/24,000 mile maximum ATF change routine to maximize your odds of getting good life out of the thing.
John
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John Horner wrote:

Cool, thanks. I just wanted some corroboration because it feels a little weird. then again, I'm pretty much a stickshift snob, and if I have to drive an automatic I would prefer that it chirp the tires when it shifts :)

I don't :/

Is there any advantage to switching to synthetic after the car has had a chance to break in? I haven't decided yet if I'm going to buy it out when the lease is up; I understand that the deals offered for buying out your own company car are often decent and it would be nice to have a car that a) I'm not tempted to spend lots of $$ hopping up and b) has few enough miles and/or has been maintained well enough that it can be considered dead-nuts reliable...
nate
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Just give it a few years and over 150,000kms, it'll start chirping between gears. Mine does it, been doing it for a couple of years now. Pretty sure it's the common problem I hear other people talking about, but I don't want to fix it. It gives those rice burners a little reality check because sometimes, if I time it right, I can cruise at about 40km/h, give a little throttle so it downshifts to first, gets the rpms up then go WOT so it basically shifts to second at the same time the car launches and she'll let out quite the chirp. Other than that, she'll chirp 1st to 2nd everytime from a dead stop at WOT.
Steve
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Steve Mackie wrote:

"chirp" the tires at WOT? Man, you need a real car. Or more power. It takes two nice hundred foot patches of sticky rubber to make me grin. (or is that one nine hundred foot patch? My old Firebird could probably lay a 900 foot burnout with it's pegleg rear end...)
;)
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"Chirp" between gears, not from a stop....
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My view is that you pick up a little bit of safety margin with synthetic transmission fluid. However, GM recently upgraded the requirements on the conventional Dexron ATF to "Specification H". Personally I use major brand conventional ATF and change it at least once per 24,000 miles using the poor man's flush method of removing a fluid line at the radiator and using idle power to pump out old fluid while adding new. Takes about 1 case of ATF to do this on our Silhouette. I case of Chevron Dexron ATF is about $15 at Costco, so this is not an expensive thing to do.
> I haven't decided yet if I'm going to buy it out

There are some things which maintenance does not ensure reliability of ... like the A/C condenser which is presently being replaced on our '02 Silhouette at a cost of almost $1000 (stealership pricing here in Sunny California).
John
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My 2003 Grand Prix 3.8L has 40k on it and the tranny fluid is still pink and clean. Never has been changed out...

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culfan wrote:

We had made a highway speed trip through the Rocky Mountains into Colorado when our acquired the burnt smell, so perhaps those demanding driving conditions had something to do with it. Also, the 3.4 L powered minivan is quite a lot harder on the drivetrain than is a Grand Prix all other things being equal. More weight, higher revs required to get power from the engine, more wind resistance and often much higher passenger + cargo loads. Minivan service for passenger car drivetrains is really pretty hard on the components.
Personally I feel that spending $15 once every 18 months or so to replace the ATF plus around $10 for a transmission filter is a bargain basement bit of maintenance to do. Heck, it costs almost $50 to fill the fuel tank on our Silhoette. One of the reasons I enjoy doing my own routine maintenance is that I can maintain the vehicle more agressively than by-the-book while still having out of pocket expenses much lower than those who pay to have the work done.
My experience is that automatic transmission failures are more common on modern vehicles than are engine failures, and the cost of replacement is very high. But hey, do whatever you want!
John
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