5l40e transmission question

[Spykem4e]

Hello guys! I'm not very used to that transmission and since I have the car, I always questionned the transmission. On my 05 cts 3.6l, there's a 5l40e transmission drive-by-wire.

My question is this: Is this normal that when hitting full throttle, there is a delay between the 1st and 2nd gear? I dont think the transmission is slipping because it would cause the engine to over rev a bit but thats not the case. Between the 1st and second gear shift, you can see the rpm drop and there is like what it seems a second delay before the transmission kicks in (feels like a manual transmission).

That was my first question and the second one now:

Again with the transmission... When hot outside and when ONLY the a/c is working, coasting downhill between 70-90 km/h, the tcc seems to unlock and lock (only once). (the rpm goes to 1900 rpm to 1000 rpm and just go back to 1900 rpm). At 70 km/h, the engine and transmission when coasting down a small hill try to maintain the speed I guess but you can see the rpm drop from 1500 to 900 and then go back to 1500, drop back to 900 and so on (only when at that speed). It stops if I go lower than 70 km/h or higher than 80 km/h. All that without the foot on the accelerator. During winter time, I dont use the A/c so the transmissio doesn't act like that.

Thanks a lot and hope to find some answers here!

P.S: its still a clue for the caddy forums.

 

[JTK]

The delay you describe sounds like the typical torque management you'd find with any newer vehicle, especially those with electronic throttle control. The vehicle's software and electronic hardware will take away spark, fuel or deaden throttle plate movement to reduce shock to the drivetrain. I too have owned some GM products with throttle by wire that behaved the same way. It was very noticeable on our 2005 Trailblazer. My cheapo Cobalt doesn't have ABS or traction control, yet it's 'system' will NOT allow you to spin your wheels out of control when stuck in snow/ice. It's just takes throttle control right away from you. I have no idea how it works on my Cobalt seeing as it has no wheel speed sensors.

Joel

 

[440Magnum]

Originally Posted By: Spykem4e
Hello guys! I'm not very used to that transmission and since I have the car, I always questionned the transmission. On my 05 cts 3.6l, there's a 5l40e transmission drive-by-wire.

My question is this: Is this normal that when hitting full throttle, there is a delay between the 1st and 2nd gear? I dont think the transmission is slipping because it would cause the engine to over rev a bit but thats not the case. Between the 1st and second gear shift, you can see the rpm drop and there is like what it seems a second delay before the transmission kicks in (feels like a manual transmission).



Torque management in action. Modern vehicles with "throttle by wire" (where the actual throttle position is controlled by a servomotor under computer control) will actually close the engine throttle while the automatic transmission is shifting, which limits the heating the transmission clutches have to absorb. Back in the old days, big block v8s were backed by beefy 3-speed automatics and a wide-open upshift would dump a big spike of heat into the clutch packs as the clutches dragged the engine down from high RPM to low during the shift, all while the engine was delivering near its maximum torque. Those transmissions were tough and reliable (Mopar Toqrueflite, Ford C6, GM TH400), but big and heavy and drew a lot of "parasitic" power from the driveline to move the big internal parts. During the early 90s, manufacturers moved to much lighter internal components for automatic transmissions, which results in much greater efficiency. The cost was that they don't tolerate abuse as well. Transmission life and reliability was *greatly* improved by simply using the computer to cut the engine power during upshifts, with no other mechanical changes to the transmission. Cars that don't have throttle-by-wire still may have torque management in the form of cutting fuel injection pulses during upshifts. The first vehicle I owned that had torque management was my wife's 93 Chrysler LH series, and it used fuel injection shutdown. Newer systems are much nicer and result in smoother shifts, but you can hear them working more and as you say it seems very much like a manual transmission being shifted quickly and precisely.

 

[Win]

1. Yes. The 5L40E A5 in my G8 also has torque management (LOL, it's only about 255-260 ft-lbs) and you can definitely feel it on the 1-2 shift, although it is not as severe as you describe.

2. Don't know, doesn't sound normal.

You might want to have your dealer see if the firmware for the transmission needs to be updated.

 

[Spykem4e]

Thanks guys for the quick answers! 440Magnum, thank you or explaining the way it work and its exactly how the transmission/engine are working! I cant ask more for an answer!

Win, for the tcc lock unlock problem, no dealer can find anything wrong with the transmission. They see it act, but can't figure out and can't find any firmware or update or new program for my transmission. I'm out of idea now and getting very tired of this!

 

[Spykem4e]

bump!

I think its not TCC related because I can see the rpm drop when applying the brakes pedal.

What could cause the transmission (you feel the the gear releasing, engaging, releasing, engaging) to pass from 1500-1750 rpm and drop to 1000 rpm and then back up to 1500-1750 and drop back to 1000 and so on when I'm between 70mk/h and 80 km/h, coasting down a hill with no foot on the gas pedal (HVAC on only).

It does the same thing but only once when releasing the gas below between 80-90 km/h. 90 km/h and more, no problem so I dont thinkits the transmission itself the problem. I'm just looking for what could be causing this.

Right now, its winter so the air conditionning is not working so I dont have any problem with the rpm drop. It happened once this week because the A/C was running once. And All summer last year.

I just want to figure out if its hurting the transmission and if I can try to fix things.

 

[mstrjon32]

Originally Posted By: 440Magnum
Those transmissions were tough and reliable (Mopar Toqrueflite, Ford C6, GM TH400), but big and heavy and drew a lot of "parasitic" power from the driveline to move the big internal parts.


Ugh. I hate modern cars.

Those were the days, 3-speed automatics that you could beat on all day, and if by some chance you did break one (maybe by say, downshifting it into 1st on the highway to do a nasty burnout) it was easy to remove and cheap to rebuild.

I promise, one of these days I'm selling my car and buying an old project car.

 

[JTK]

Originally Posted By: Spykem4e

What could cause the transmission (you feel the the gear releasing, engaging, releasing, engaging) to pass from 1500-1750 rpm and drop to 1000 rpm and then back up to 1500-1750 and drop back to 1000 and so on when I'm between 70mk/h and 80 km/h, coasting down a hill with no foot on the gas pedal (HVAC on only).


First of all, it's a 5spd auto. They tend to be busier than most with regard to the amount of gear changing. 2nd, all the 5L40's that I'm aware of have pulse width modulated solenoid control for the torque converter lock. The SLIGHTEST load change or throttle position change to the engine will cause the TC to unlock and drift back into lockup (pulse-width style). A/C compressor cycling will cause load/throttle position to change, prompting your trans to downshift, unlock/re-lock the TC, etc.. It's sounds all normal to me.

Joel

 

[Win]

Originally Posted By: JTK
Originally Posted By: Spykem4e

What could cause the transmission (you feel the the gear releasing, engaging, releasing, engaging) to pass from 1500-1750 rpm and drop to 1000 rpm and then back up to 1500-1750 and drop back to 1000 and so on when I'm between 70mk/h and 80 km/h, coasting down a hill with no foot on the gas pedal (HVAC on only).


First of all, it's a 5spd auto. They tend to be busier than most with regard to the amount of gear changing. 2nd, all the 5L40's that I'm aware of have pulse width modulated solenoid control for the torque converter lock. The SLIGHTEST load change or throttle position change to the engine will cause the TC to unlock and drift back into lockup (pulse-width style). A/C compressor cycling will cause load/throttle position to change, prompting your trans to downshift, unlock/re-lock the TC, etc.. It's sounds all normal to me.

Joel


That's sure not how the 5L40E in my G8 reacts.

It does not hunt for gears at all, and, frankly, it does not need to, nor does it need to unlock the convertor very often. The high feature V6 has a lot of torque, spread over an extremely wide powerband.

Notwithstanding its modest displacement, it's really a little torque monster.

 

[JTK]

But it's a different vehicle from the OP's 2005 Caddy.

Joel

 

[Win]

Not so much.

Same transmission, AFAIK. The high feature V6 has had some running changes and improvements since 2005, but nothing that would account for the OP's odd behavior.

Or, HydraMatic has made enormous strides in just three model years, because the type of erratic and mediocre performance you are suggesting as normal simply could not be farther from the truth in my experience, based on the 5L40E in my G8. The ZF 6HP26 in my wife's XJ8, a design that is now nearly six years old, doesn't act crazy, either.

 

[Spykem4e]

Well.. after couple of days of research, I can only say thank you guys! I've read everything and I've searched the net for my kind of transmission and find out that bmw uses this transmission. I went at a bmw dealer and the tech said that is not normal. He test drove the car and saw the weird rpm droping and increasing at 70 km/h.

He said that he saw that thing once on a bmw and it was the programming that was wrong when there is xx % of load on coasting. I took an appointment and he'll put his scan and try to find what is asking for too much load and reprogram the transmission with the new load range.

 

[Spykem4e]

is there a way to change the data or to reflash the ecm or the a/c ? I mean even the bmw dealer couldn't change the weird behavior.

Is there somewhere, if I take a tech2, that I can see why only when the a/c is running, the transmission will unlock and lock between 70 and 85 km/h? With a tech2, if there's a table where I can change the information regarding the tcc and the load when coasting.

We did a lot of road tests and even with the front and rear defrost + heated seats on etc everything is alright. The problem occurs only when the a/c is on and you take your foot off the gas pedal between 70-85 km/h.

 

[Spykem4e]

okay, I'll try something else hehe

Could a bad idle speed sensor valve be the reason why the tach bounce? Let say the idle speed sensor valve or I'm not sure how to call it, was not fast enough to do its job when the a/c is cycling on/off.

I'm searching on the net and saw some problems with that sensor and MAF sensor.

 

[toyota62]

ECU/TCM Software upgrade?

 

[Spykem4e]

Toyota62, I've done all the update upgrade from GM. Unfortunately no one knows what is going on. From the CTS Forum, I'm not the only one with the issue and no one seems to have an anwer for that.

I did some other testing like putting the car in neutral position when going downhill and the rpm's goes to normal operating revolutions (650 rpms) and stays there.

What I found out is this: when I put the DIC on inst. mpg reading, Usually when coasting (foot off the throttle) it says 0L/100km (normal) but between 40-55mph with the a/c on (to make the bouncy tach) the rpm goes to 0 L/100km and and when it bounces back up, it reads 5-6L/100Km and so on.

Could a bad idle speed sensor would be able to do that if it was faulty just a little bit with only the a/c on?

I dont know where to search anymore. Is there voltage I can check to see where is the problem seems to start?

At Canadian Tire, there's an OBDII that I want to get for 299$ and it tells you throttle % etc. I dont know if it can help or not.

If you say no it wont, I'm gonne borrow a tech2 from a GM friends very soon.