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Discussion Starter #1
I've noticed something odd with my tachometer, when I'm driving, and it doesn't seem to matter what gear. If I let off the gas a little and let it drop about 100 rpm, then give it gas again, it jumps up about 300-500 rpm, then drops back down to about where it started.

On the highway it's real easy to do, I just let off a little then ease back into it and it jumps.

But I've noticed it when getting on the highway under moderate acceleration and also at other cruising speeds. Under harder acceleration it's less noticeable, but I've seen the needle fluctuate up and down a little.

I'm not sure if it's in the engine, its hard to hear the minor rpm change, I'll have to hook up a separate tach and see if it's there also.

I do hear some noise from the tranny under load when cruising though as when I shift to neutral it goes away and giving it gas doesn't make it come back. Put it back in gear and I can hear it again, more so when I give it gas.

Steven
 

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Sounds like the torque converter might be going out of lockup when you apply the gas, thus some apparent 'slipping' and the slightly higher revs until it locks up again.

I've seen some vehicles do that quite regularly. (seem to recall our old Chevy S-10 Blazer behaved like that) You can get used to it or change your driving style.
 

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Sound like torque converter unlocking and locking. Sounds normal to me.

I actually momentarily lift my foot on the gas pedal after every acceleration to help the torque converter lock up earlier for better mileage. I've found that by watching the instantaneous gas mileage readout, I'm better able to judge when to lift my foot a twitch and get it locked up. I'll be watching, mileage reading is 16-17 mpg, lift the foot for a second, mileage jumps 5 mpg. Resume pressure on the pedal and mileage holds at the higher number. I find this easier, than trying to watch the tach to detect the converter locking.

It's a game of keeping it locked as much as possible for best mileage.
 

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This is definitely an effect of the lockup clutch in the torque converter. I've never had a vehicle where it was so obvious as to when it's locked and unlocked. Accelerate to highway speed, and after a moment in 6th you'll see a 200-300 rpm drop as the converter locks. It's almost like having another gear.
 

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Discussion Starter #5
OK, then is what's going on normal? Or abnormal?

I've never had a vehicle with an automatic and a tach do such a thing.
 

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It's completely normal for a modern auto trans.

It wants to be locked up when the system is transmitting power whenever it can, for better mileage, less heat in the transmission, etc. It wants to be unlocked below a certain speed to do its torque-converting when starting off from a stop, and it wants to be unlocked during gearshifts to smooth them out. Normally the torque converter is left unlocked in the lower gears for smoother operation.

It unlocks when coasting and particularly when the brakes are applied, because there no need for it to be locked (there is no fuel to be saved by locking it) and it is smoother that way. If you slow down enough to warrant a downshift when you begin accelerating again, having the torque converter unlocked allows that shift to be done promptly without waiting for it to unlock first.

If you coast or brake for a bit (converter unlocked) and then you re-apply accelerator, it leaves the torque converter unlocked for a moment to allow the engine to take up the load without an annoying jolt. Converter lock-up has to be done progressively to avoid another jolt, this is why the revs go up a bit (unlocked) then come back down (locking).

These modern transmissions are much, much, MUCH smarter than the old skool transmissions that left the torque converter unlocked all the time unless it was in top gear above a certain speed ... and it's part of why a lot of automatics have better fuel consumption ratings than manuals do.

You can see more of the smarts at work if you accelerate to around 70 km/h (45 mph) then ease off to a steady speed. It spends a couple seconds in 5th gear - converter locked. Then you see the revs rise for just a moment - converter unlocking - then it does the 5-6 gearshift together with locking the converter and the revs come way down, and it does so very unobtrusively.
 

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Discussion Starter #7
Hey Brian,

Thanks for the detailed explanation, I was thinking about the same thing, just never experienced it. And your right, I'm used to a trans that just locks up in the final gear, not every gear.

Will say though, it did bang once, can't recall how or why as it surprised me.

Steven
 

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You can sometimes catch it out if you do something with the accelerator at the very moment that the transmission controller is in the midst of doing something else.

Also, the 2-3 shift can sometimes be awkward. More techy stuff follows ...

At its heart, this transmission is a glorified 4-speed automatic that has had an extra planetary set so that there are 8 possible combinations, a "low" and "high" in each of the 4 possibilities for the main gear set ... but it only uses 7 of them. Two of the combinations work out to be the same ("4th underdrive" is the same as "3rd direct") so obviously one is not used. There are two possible 4th gear ratios ("2nd direct" and "3rd underdrive" if you will) that are very close, and it will pick either one depending on circumstances but it won't shift through both of them. Essentially the 6 (7?) useful combinations of the main 4-speed box together with the underdrive set are "first underdrive", "first direct", "second underdrive", "second direct" / "third underdrive" (depending on circumstances), "third direct", "overdrive direct".

First awkward side effect ... Second and third (or "first direct" and "second underdrive" if you will) are close together, the overall ratios are around 2.8 and 2.2. That alone makes the 2-3 shift a bit awkward.

Second awkward side effect ... To make that shift, it has to shift the main 4-speed box from first to second, and it has to shift the underdrive box from direct to underdrive, and it has to get the timing right. Might not always happen perfectly.

It avoids a similar awkward side effect during upshifting by selecting "second direct" as the 4th-gear in that situation (avoids shifting the underdrive box), and it avoids it during downshifting by selecting "third underdrive" as the 4th-gear in that situation because that avoids possibly having to do a subsequent awkward downshift.

Another awkward side effect is that whereas 2nd and 3rd are too close together, 5th and 6th are too far apart.

The 9-speed ZF box that Chrysler is using in some other models isn't a glorified 4-speed automatic, it was designed to have that many speeds. But it has its own idiosyncracies. It uses two dog-clutches without synchromesh. Upshifting is not an issue because that involves disengaging the dog-clutches, but the 8th-to-7th and (I think) 5th-to-4th downshifts are awkward because it has to rev-match using the engine to let the dog clutches engage. If you are cruising in 8th and mash the accelerator to the floor, it could very well have to synchronize both dog clutches to get (say) 4th or 3rd in one step. Meanwhile ... you wait! I haven't driven a car with that box, can't say how much a bother it is personally.
 

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Man! Good stuff.

To be honest, the trans is my one niggle about the pm. It feels clumsy, it masks a good engine, and it can be easily confused. Cruise control or not, the trans seems always eager to engine brake on big hills. I know its doing this to save the foot brakes, but its annoying.

I was assuming that over the next couple of years the chip programmers and tuner crowd would come out with a box that allows reprogramming the shift points.

Ewww i just got inspired. When it comes time for a rebuild, have it converted to a full manual valve body, and then shift it with two sticks like a dumptruck driver with a two speed rear. Suicide shift!
 

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Man! Good stuff.

To be honest, the trans is my one niggle about the pm. It feels clumsy, it masks a good engine, and it can be easily confused.
Was it that way from day one, or did it get worse with age?

I ask because mine is so smooth and nice, but I've only got 3000 miles on it. If it turns rough later on, I'll do my usual trick that fixed my Ford trucks. Change the fluid at 30,000 miles. After that they were like new again. It cured 2 Fords.

Or maybe they tweaked the tuning of the tranny on later production. Mine was build on 6/14.
 

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I think it is the nature of the beast. I'm in tune with vehicle calibration because I have the misfortune of being a mechanical engineer who works in the auto industry (although I'm on the automation/robotics/tooling side of things), and also my motorcycle roadracing hobby has me doing a fair bit of "calibration" on the bikes ... so I notice things that other people might not, but also often understand why something was done a certain way.

The 62TE does work well for what it is, and I understand why it was built that way. The 4-speed main box started out as the Chrysler "Ultradrive" some 25 years ago ... and it did not have a good start. The simplest way for Chrysler to get with the trend of more speeds in the transmission about 8 or so years ago, was to add that range box to the existing gear set. Transmissions tend to not change much over time and no one wants to re-invent the wheel, particularly for such a hidden-from-view system. It has some good features, including progressive control of the lock-up clutch, it isn't simply "on" or "off", that helps with shift smoothness.

As for glitches ... There is not a single automatic transmission out there, that can not be "caught out" because the driver did something that the transmission controller was not expecting. CVT doesn't solve this ... actually, they're often the worst offenders. I suppose you can argue that the single-speed gear reduction that most electric vehicles use can't be caught out because there's nothing for it to be caught out by. The Prius drivetrain is somewhat similar; it can use the EV part of it to overcome it if the engine is off or running at the wrong speed. They're also the most dull vehicles that can possibly be imagined.
 

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Stuck at low gear

Hi all,
My PM had an engine light on and a message on the dashboard said need engine check. The dealer ran diagnosis and replace a sensor in the transmission, he test drove to make sure all gears shift smoothly. Then I got the PM back and drove for one 1hr trip. The next day I start drive again, the transmission stuck at low gear, push the gas pedal, the engine rpm roar to above 4000rpm and the speed only 40mph on the flat road. I stop and tried to engaged all the gears but still stuck in low gear when in D. Then I turn off the engine wait for 5 minutes then start again, the engine check message come on, and luckily the D gear is working as normal again, I can drive back home safely. I bring the PM to the dealer for service.

My question to the forum is if anyone has experienced this problem before? Is it serious defect in the transmission? Since it still under warranty should I request to replace the transmission or not? I am worrying if I am on the road trip and the transmission fail again then it will be a big problem and it ruin my summer vacation.

Any opinion would be appreciated.
Tuan
 
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