started up after being gone a week for t'giving...ses lite came
on :eek: ...after letting engine warm up, put in gear...VERY sluggish move off...same response from stop lites...no acceleration from dead stop, then drove ok...

when parking in restaurant lot, it wudn't go into reverse...had to have it towed to $tealer :( ...they've always done good work in the past, and opined that (they hoped) it was a bad module, and NOT the transmission Censored ...i've not heard from them yet :confused:

any opinions?

Converter drain back is the culprit. GM is well aware and there is corrective measure.
If you dealer is unaware check the TSB forum there was a copy there.

Good Luck!

Mackin is correct.
To explain briefly, in automatic transmissions there is a check valve (usually in the front pump assembly) to prevent the torque convertor from draining back into the transmission while not operating. As the torque convertor is fluid driven on the trans side, & the trans pump (which supplys the fluid) is driven by the torque convertor, you can imagine the troubles that a lack of fluid in the convertor would create (ie-no fluid in the convertor to drive the pump properly=insufficient pump operation to supply fluid to the convertor-a catch22 of a sorts). Apparently there must have been a design flaw with the Allisons as this seems to be a common problem with them (already had mine repaired under warranty), the problem usually occurs when vehicle is parked over time. Your perfect description of the symptoms you experienced should clearly indicate the problem to anyone familiar with auto transmissions, if the dealer can't seem to locate the trouble, tell him yourself were it is (I had to)
Hope this helps you.

Had a similar situation with a 200l 8.1 with Allison. Truck sat for a few days on level surface. Would not go into reverse when started up. Moved it forward a bit, tried reverse. No Joy. Got on On-Star to get a tow. Fired up once again and got some backing movement. After a short time all cleared up. Never had the problem again. Had truck in dealer to change out alternator that had bearing problem and tech said he heard a abnormal sound in torque converter. Replaced it. May have been cause of original no reverse problem. Don't really know.

is there a recall on the allison to correct the problem? I don't want to get stuck somewhere because I let the truck sit for a few days.

NO recall..........but a TSB for a problem tranny........

Transgo addressed the problem in the rebuild with a new spring assembly......

If you are out of warranty and need to go in the tranny then upgrade the tranny while it's out.

T:cool: NY

Torque converter drained back on mine after sitting 2 weeks. Doesn't cause a problem if I drive it at least once a week. Is there any damage can be done if this is not fixed? Seeing that mine is no longer under warranty, the stealer wants $800 to repair.

Had it happen to me also. Has not happened for about a year now. I am not sure if it is related to how one drives or just a spuratic case.

IF your out of warranty, then the fix is easy. Start the truck and let it run for 3-4 minutes after sitting that long. That will be enough to fill the circuits back up and no problems.

Hopefully it's not as bad as mine was.
I let mine run (idling that is, wouldn't do much but slip in forward gears at first, no reverse at all) for over a 1/2hr & it was not much better. Had to wait about an hour, & I still had to drive it (still slipping slightly) for at least another 15min until it seemed o/k. Light didn't go out until 2nd restart.

That truck was getting driven straight back to Dealership on it's own steam no matter what. No way I was gonna put the new +40k chevy truck I'd been bragging so much about on the bed of one of my wreckers for all my furd luvin' friends to see. I'd never be able to live that one down. No sir, I'd burn it before I did that.

& after all that. Dealer's advisor calls me later that afternoon & tells me "We can't find any problem" - yeh right. He must have just been lazy because that exact problem is discussed in Automatic Trans class 101 in the first week, everywhere. No way those techs wouldn't have known.

Mine started at approx. 800 miles but, I ignored it thanks to forums like this, until about 33.5k miles (decided to get it fixed under the original factory warranty). Never had a problem if I drove it every day or so and, over half of this mileage was towing a 9000# travel trailer.
Richard

my old 79 Dodge Ramcharger 4X4 (lake truck) has the same issue with its 727A torqueflite transmission. The trick is to put it into neutral and allow it to pump up the transmission circuits for about a minute and then put it into gear. If you leave it in park it WILL NOT pump up the circuits on the torqueflite. Maybe the allison is the same and it needs to be put into neutral to allow the circuits to fill up.

BTW, the trans pump is driven by the outer shell of the torque converter (not the inner turbine which drives the input shaft to the transmission) which is mechanically coupled (bolted) to the engine. Think about it, when you come to a complete stop with the engine running, the input shaft to the transmission comes to a complete STOP. This is because the fluid coupling effect is low enough at idle to allow the inner turbine/stator (term ?) to stall, while the outer one (part of the outer shell of the torque converter) to continue to rotate. IF the trans pump were driven by the inner turbine/stator and the input shaft, it would stop pumping and loose all pressure in the transmission :eek: . How do I know you ask...... I've rebuilt so many of them in my younger days I can rebuild a torqueflite in my sleep now (used to race and abuse them pretty hard back then).

Now if you ask, why don't I fix the Ramcharger??? Well it stays up at our lake house and is only used to drive about 1/4 mile down a trail to the beach. It gets about 300 miles a year put on it so its really not worth the time to drop the valve body and replace the check ball and spring that keep the fluid up in the torque converter. If I ever blow the tranny, then that will be the time to fix this little issue.

Next time it drains back, try putting it in neutral and see if it pumps back up vs leaving it in park.

Excellent description Searay90 :ro)

So I think we can agree that with insufficient fluid in the convertor (due to drainback), fluid coupling would be severly reduced (if present at all) limiting pump operation (which operates via fluid coupling) thereby reducing both supply & pressure. :)

It's been my experience that the amount time & the degree of incline these vehicles are parked, determines the severity of the symtoms. :(

Have a great holiday everyone.

Point of clarification: Fluid coupling has nothing to do with the pump operation, its driven by the outer shell of the torque converter.........not the input shaft. The transmission could have absolutely no fluid in it and the pump would still operate at the same RPM as the engine. That the danger about starting an automatic tranny with no fluid in it, you WILL Burn up the pump in a matter of seconds. But if the allison is like the torqueflite when in park all it is doing is curculating the fluid back to the pan and not pumping it thru the torque converter and trans circuits. This makes sense to me as you DON'T want the torque converter and or any clutches doing anything when she is in park !! Now when the torqueflight is in neutral, it IS pumping fluid thru the torque converter, but the cluthes are not engaged so you still don't "move", but fluid it being pumped thru the torque converter, and the innner turbine is moving. Hopefully someone watching this thread will try the "run in neutral" trick next time this happens and see if it works.Excellent description Searay90 :ro)

So I think we can agree that with insufficient fluid in the convertor (due to drainback), fluid coupling would be severly reduced (if present at all) limiting pump operation (which operates via fluid coupling) thereby reducing both supply & pressure. :)

It's been my experience that the amount time & the degree of incline these vehicles are parked, determines the severity of the symtoms. :(

Have a great holiday everyone.

Mines did't reverse eaither, but I was driving the truck for an hour already when it happened, i was going to park and the reverse didn't work any thoughts on this?

Searay90

Go back and ask the guy that gave you that info to repeat it. You did not get that stuff out of a book. Input shaft never stops turning. Your explanation of how the automatic trans works is like an act of God. I have a hard enough time fixing them when they are designed and made by man. I am not near good enough to handle His design.):h
mike

Mike, Don't understand your question. :confused: "Go back and ask the guy that gave you that info to repeat it. You did not get that stuff out of a book. Input shaft never stops turning"

Maybe we have a disconnect on the term "input shaft" ? I am refering to the input shaft to the transmission. The one termed "turbine output shaft connects to transmission" in the picture below.

http://static.howstuffworks.com/gif/torque-cutaway.jpg



When you are in drive, and stopped at a stop light, "the input shaft of the transmission" does in fact stop turning. If it didn't stop turning you would not be able to stop the truck without stalling the engine. Think of it like a manual transmission. If you don't disengage the clutch when you come to a stop, the engine stalls. In an automatic, the torque converter coupling "stalls" which allows the outer shell (which is mechanically coupled to the crankshaft) to contiune to turn. The input shaft to the tranny stops turning because the fluid coupling stalls (the analogy of pushing the clutch in on a manual transmission). An automatic transmission does not put itself into neutral when you step on the brake and come to a stop. When you are in any forward or reverse gear and come to a complete stop, the ONLY thing turning inside an automatic transmission IS the PUMP, nothing else moves. Not the input shaft, the planetary gear sets, clutchs, or the output shaft. Now if you put the truck in neutral, the input shaft will in fact turn, and the planaterys gear sets will start turning, but the planaterys are allowed to "over run" each other because a clutch (or band depending on trans design) is not locking up one part of the planatery. Thus no transmission of power thru the planatery gear set.

It is the outer shell of the torque converter that drives the pump "within" the transmission (the one that powers all the hydraulic circuits within the transmission), NOT THE INPUT SHAFT OF THE TRANSMISSION. The input shaft to the transmission is FLUID COUPLED to the outer shell of the torque converter via the use of stators, turbine wheel, and the AFT fluid itself. When you stop the truck in drive, the Turbine stalls because it is mechanically locked to the input shaft via the input shaft splines. The outer shell of the torque converter (and its stator) turn at engine speed. The two stop turning together and stall, this is what generates heat when you are stopped. One turning, the other not. Torque converter stalls, heat is generated.

BUT the pump in the transmission never stops pumping fluid because it is driven by the outer shell of the torque converter. If you have ever replaced a torque converter you know that the hardest part of getting it lined up in the tranny is getting the notched neck on the torque converter properly lined up with the tangs on the pump itself. You can only get it lined up in two positions which are 180 degrees apart. The input shaft has numerous splines on it and will engage in any of the 360 degrees you can line it up at. Same with the transmission side stator (the larger hollow shaft on the transmission side that the input shaft sticks out of). It is splined and will engage in just about any position you rotate the torque converter to.

Take a look at this if you still don't understand what I'm trying to get across.

http://auto.howstuffworks.com/torque-converter2.htm

"Act of GOD" design??? come on........... It's one thing to be able to fix a transmission, it's another thing to understand how it actually works and what each of the components within the tranny are doing at a given time to provide you with multiple forward gears & reverse. I've studied diagrams of the hydraulic circuits that are not contained in your average transmission repair manual. I didn't design the automatic tranny, and my hats off the to folks that did....... it's impressive. But i have studied what they did and I understand how it works (long before the internet put up sites like the one I listed above).

Searay90

Go back and ask the guy that gave you that info to repeat it. You did not get that stuff out of a book. Input shaft never stops turning. Your explanation of how the automatic trans works is like an act of God. I have a hard enough time fixing them when they are designed and made by man. I am not near good enough to handle His design.):h
mike

Allow me to rephrase, what I meant to say was that these trannys seem to lack the proper mechanisms (decent check valve) to hold fluid in the converter (probably also in the pump). It is this lack of fluid which is responsible for the symtoms described in this thread. I have not had the opportunity to disassemble an Allison1000 yet, so I do not know if it is possible for the pump to lose it"s "prime" & have a diminished capability when fluid is not present but that is sure what it feels like to me. As I said before, time & incline seem to determine severity, which seems to determine the rate of recovery.

Sorry for the previous sloppy description (I was very tired) & the incorrect reference regarding fluid coupling & pressure pump operation. I must have had my brain stuck on the converter pump (impeller)

Yes Searay90, you are right about the converter housing driving the pressure supply pump (see below), but without fluid in the pump itself (ie-faulty check valve), what would create the initial pressure required for proper/timely pump operation? certainly not the "air" it would be sucking. Wouldn't this be similar to an event in which an engine oil pump with a faulty check valve loses it's prime & is then unable to recover on it's own in a timely fashion? (at least not in a sufficient amount of time to be certain no damage may occur if undetected)

Any thoughts please.




<B><BIG> </B>
<B><BIG>Oil Pump</BIG></B>

The transmission oil pump (not to be confused with the pump element inside the torque converter) is responsible for producing all the oil pressure that is required in the transmission. The oil pump is mounted to the front of the transmission case and is directly connected to a flange on the torque converter housing. Since the torque converter housing is directly connected to the engine crankshaft, the pump will produce pressure whenever the engine is running as long as there is a sufficient amount of transmission fluid available. The oil enters the pump through a filter that is located at the bottom of the transmission oil pan and travels up a pickup tube directly to the oil pump. The oil is then sent, under pressure to the pressure regulator, the valve body and the rest of the components, as required.

</BIG>

If the fluid level is correct in the tranny, the pickup for the pump (the tranny filter) will always be submerged in ATF. The pump is a positive displacement pump and it will self prime itself just like an oil pump on a car (which is not submerged in oil, but sits up above the oil level in the oil pan).

The check valve we are talking about keeps gravity from emptying out the torque converter when you turn off the engine. I don't know the exact capacity of our torque converter, but I would say about 2 gallons at least. So when it "drains down", about 1/2 of the torque converter is empty of fluid.

So now you have a torque converter that is turning at 750RPMs that is foaming up with 1/2 ATF, and half air. Not good for providing a "fluid coupling" environment. So it is up to the tranny pump to fill up the torque converter and flush out the mixture of "air entrained ATF" that is in the torque converter upon start up.

As mentioned in one of my earlier posts I know how the old 3 speed torqueflite transmission accomplish this. It WILL NOT HAPPEN with the transmission in park!! , it will only fill the torque converter back up with the tranny in one of these positions R,N,D,2,1 If you use any position other than N, you are making the clutches, bands, torque converter "slip" because there is not enough pressure and oil flow to make them work properly. So on my old 79 Ramcharger, I just put it into N with the engine running and let it idle for about a minute or so, then put it into R,or D and the tranny works perfectly because when it's in N the pump will fill up the torque converter and all the hydraulic circuits in the transmission.

NOW the BIG question is wether or not the Allison behaves in the same manner........... ?? Does it behave like the torqueflite in that it does not pump up the torque converter while in park? Does it try to self protect itself when you put it into a drive position and it sees that pressures are low, or that it is sensing "slippage" and goes into some type of self protect mode??? I don't know :(

All I am SUGGESTING is that the next time someone has this problem, Do the following to see if it works.

1) Immediately shut down the truck.
2) Turn off the key.
3) Wait 30 seconds or more
4) Restart engine and immediately put the truck in Neutral
5) Allow it to idle for at least 2 minutes
6) Put in R or D and see if the issue is solved (ie the truck moves/drives normally)

If the above works, then the allison has the same fix as my old torqueflite does for torque converter drain down and the owner can decide if they want to pay the money (assumed your out of warranty now) to fix it, or just use the method above when it happens to you.

Now if this does not work, then it's probably due to the "computer controlled/electrically actuated valves" nature of the Allison vs the "Mechanical" nature of the valve body in the old torqueflite.

I hope someone comes back to this thread at some time and lets us all know if the procedure above actually works or not :)

This board is all about learning from each other, and helping find solutions to problems that GM won't address. I have learned quite a bit about the uniqueness of the DMAX/Allison on this board and look forward to reading new things on it every day.

searay90,
It has been my experience that most so called "self-priming pumps" (such as gear type positive displacement) do not self-prime adequetly (if at all). Most all of the oil pumps i've encountered contain a residual check valve of some type to prevent drainback & the subsequent loss of prime-if they were truly self-priming, why would they need a check valve? (the pump that is)

Any literature on engine machining/rebuilding that I have ever seen will instruct you to "prime" the lubrication system before intial start (before powered engine primers became available, we used to prime engines by packing the pump cavity with vasoline-a pure petro jelly, it harmlessly disolves in other petro products-in order to achieve pressure immediatly). I have seen many a rebuilt engine damaged by peoples failure to prime the lube system beforehand. These engines all had gear type positive displacement pumps with residual check valves. Harley V-twins seem especially prone to this type of trouble (ie-people failing to prime the system after rebuild with premature engine failure being the end result)

As I do not have experience rebuilding Allisons, my question was; could the same drainback problems concening most mechanical pumps i've encountered also occur in the Allison, causing a more "extended" time interval between the intial detection of the issue & the recovery? :confused: (we already know the effects of reduced fluid presence in the converter)
I am pondering on why it takes so long to recover.
Is it possibly due to fluid "foaming" in the converter from the cavitation caused by reduced fluid presence? or is it a loss of prime in the pump itself?
I would like to know if anyone has the answer please?

Have a nice holiday.