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Old 08-24-2009, 02:19 PM   #1
KathyandDave
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Duramax/Allison shifting problem

Several times, after multiple stop-and-goes in traffic or multiple smaller hills, in tow/haul mode, the transmission will not shift up until we pull over and idle for a while. The only telltale is the transmission temp, which gets up to 86-94 degrees C (187-201 degrees F). No lights or warnings. The CGVW is within spec for the TV (per manual). Speed is low. Outside temperature varies, but never above 90F. Any ideas?
 
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Old 08-24-2009, 03:29 PM   #2
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Sounds like your transmission is going into the LIMP MODE. It will do this if it detects something wrong in order to protect itself from further damage. You will not necessary see any lights. The engine will do the same. When my fuel filter starts to clog the engine detects that and will not go over 2000 RPM. However no lights will show. If that is what is going on your dealer can read the codes that say what is wrong.
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Old 08-24-2009, 03:44 PM   #3
flstf
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Dave,
A few things to consider:
(1) Replace the fuel filter. You did not state how many miles are on your truck, but a dirty filter affects shifting due to loss of power and is felt more in tow/haul. 15k is about the life of filter (many variables impact this), but if you picked up bad fuel recently try draining the water from the filter. Follow the instructions from the owners manual.
(2) Any codes? You will need a scan tool that reads engine/body control/transmissions (such as OTC genisys). Advance Auto cant do this.
(3) Reference the miles, did you service the transmission at 5k and again at 25k (if applicable)?

Let me know the miles, whether the fuel filter was indeed changed recently, and if you have any codes and I will try to help. I am also on the diesel place.
take care,
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Old 08-24-2009, 03:45 PM   #4
KathyandDave
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Mudchief, the dealer did get the code LIMP MODE. I should have said so. On the basis of that, we replaced the fuel filter and are currently at 91% life remaining. The problem continues.
flstf, the mileage is 16,000 (26,000km). Water in the fuel is something I haven't considered. Would it have been obvious to the service tech when the filter was replaced? I don't know if the transmission was serviced at 5,000 miles (8,000km). I have naively assumed that the dealer did the requisite maintenance checks when I had it in at 10,000km (6,200 miles), but I should check this.
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Old 08-25-2009, 02:53 AM   #5
Mudchief
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How does it shift if it is not in the tow/haul mode when pulling your unit?
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Old 08-25-2009, 03:59 AM   #6
JimF
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Hope you are in the Las Vegas area, my son is a GM master and does all the Allison transmission repair there. From what he says they keep him real busy and are keeping his kids in college. It's time for school to start again sooo, Mr Allison helps him out.
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Old 08-25-2009, 04:11 AM   #7
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Ohhhh Don't say the Allisons have a problem.....they are suppose to have a reputaion of holding up real good. I hope mine is one of the ones that Good Reputation are made of. Chuck
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Old 08-25-2009, 06:02 AM   #8
Devildog
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Looking at your signature, I don't see a listing for a programmer or tuner on your vehicle. If you are running one of those, they will cause the tranny to go into limp mode when it detects consistent slippage in the torque converter. Also, if transmission is filled right up to the top of the hash mark on the dipstick, it will run hotter than normal and can sometimes cause a limp, if you are not moving or not getting alot of air. But the fan will come on alot before this happens. I have had this happen to me. Allison trannies like their fluid in the middle of hash mark range.

I just reread your post at the top, and everything is pointing to heat with multiple stop and goes or a lot of smaller hills. You should be hearing that annoying fan start up on all of those before you go into limp mode. If you're just wanting to throw parts at it, I would change the tranny filter, which is a spin on filter and pretty cheap. If you change it, which is easy, you don't even have to change your fluid, don't forget the magnet that is in the top of the filter. And that may not be a bad idea anyway, as you will see a post on dieselplace showing an aftermarket filter that the inlet holes for the fluid are not lining up properly and was not allowing fluid to circulate properly.
And as an add on, I was having my airconditioner serviced two weeks ago, and the tech stated all was correct, but the head pressures were too high. he recommended cleaning the condenser. I pulled the grill off the beast, and sprayed a foaming coil cleaner on the condenser, transmission cooler, intercooler and radiator. You would not believe the dirt that came off. And that is just from two years.

Good luck with the issue.

Another good resource online is dieselplace.com, which is a site for owners of duramax/allison diesels. Have a whole section on just the Allisons, with some good resource information and technicians that view and answer issues and problems.
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Old 08-25-2009, 06:49 AM   #9
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I would definitely go with the Allison OEM filter. We ran into problems on my son's truck when we tried another brand. Like mentioned, the magnet covered the outer holes. Those Allison filters are too cheap from the Allison dealer to use anything else. Just be sure to take the part number as some dealers won't or can't lookup the GM trucks.
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Old 08-25-2009, 11:16 AM   #10
KathyandDave
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Devildog, we haven't heard the annoying fan. Maybe it's not starting up, so the transmission isn't being cooled or maybe its coming on too late, so we're confusing it with the sound of the engine revving? One adviser said that the transmission and the engine share the coolant, yet the engine temp gauge stays dead centre while the DIC display of the transmission temp climbs rapidly. thanks for the pointer to dieselplace.com
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Old 08-25-2009, 04:02 PM   #11
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Will-- Do you have the part # for that filter incase I need to have the filter changed while I'm on the road? I'm assuming you are talking about the inline filter instead of the ban filter. I normally have the inline filter changed before any long towing experiences but incase I start to have problems....... The dealer told me we don't have to change the pan filter unless you have some reason to drop the pan. If you change the inline filter regularly and you don't have any problems with the Allison you may never have to change the pan filter in the tranny itself.
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Old 08-26-2009, 02:18 AM   #12
SlickWillie
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Quote:
quote:Originally posted by Rondo

Will-- Do you have the part # for that filter incase I need to have the filter changed while I'm on the road? I'm assuming you are talking about the inline filter instead of the ban filter. I normally have the inline filter changed before any long towing experiences but incase I start to have problems....... The dealer told me we don't have to change the pan filter unless you have some reason to drop the pan. If you change the inline filter regularly and you don't have any problems with the Allison you may never have to change the pan filter in the tranny itself.
#29539579
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Old 08-26-2009, 07:53 AM   #13
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Dave,

The engine fan makes a great roaring sound when it engages. And I think you pointed out one of your clues: Trans gauge doesn't vary that much, but the DIC shows it climbing fast. Engine fan is, don't know if I'm saying this right, but you'll understand it anyway, Hydrostatically activated. What I mean, is even with the serpentine belt turning all the accessories on the front of the engine, the cooling fan activates the clutches in it's own pulleys by an electrical or thermostat signal that will signal that it needs to come on to provide additional cooling. I hear mine every time it comes on when towing up continuous hills. It usually is on first thing in the morning when you start up, unless the hood is facing the sun, as the cool are gels the fluid in the clutches and it is drawing air until it warms up. it draws so much air, it makes a roar (best I can describe).
And your tech is somewhat correct. Coolant does not go into the transmission, but the cooling lines holding fluid for the transmission travel through the bottom of the radiator core either before the auxillary cooler you see behind your grill, or just after the cooler. Some vehicles are designed a little different, and I can't remember which one GM does. But, it is essentially a cooler and a warmer. During summer and hot temps, it brings the fluid temp to same temp the radiator is, hence if you are running hot on your engine temp, you will run hot on your tranny temp. And during the winter time, the radiator helps warm the fluid for better performance of the tranny. Think about it when it is real cold outside, seems like it takes a couple of miles of driving before the transmission feels like it is shifting regularly. It is trying to warm up by holding the gear.
So, check your fan activation and ensure that all is clean in front of your radiator, and the tranny cooler. Remember also, that using tow/haul changes the shift points to better allow the transmission to keep from upshifting and downshifting too much, and also increases your transmission fluid line flow, moving the fluid through the cooling parts more often, the assist in cooling the tranny.
Sorry for the long post, but I think you are looking in the right direction. Tranny is getting hot, slipping, and going into limp mode. Check that fan and all the other temp controls.
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Old 08-26-2009, 08:18 AM   #14
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http://www.edmunds.com/maintenance/select.html?zip=


http://www.edmunds.com/maintenance/r...b&serviceType=




this may help use your own zip code
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Old 08-26-2009, 12:38 PM   #15
KathyandDave
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cmp-shooter, that's an amazing link. I couldn't find a specific reference to our problem. Devildog, your explanation was very clear. I will look at cleanliness/obstructions to the cooling and listen for the fan. One difference from your explanation though. The engine temp gauge is reading straight up, while the tranny temp on the DIC is going like a yo-yo. In another MOC forum, somebody mentioned that a manufacturer (maybe Ford) programmed the gauges to read nice unless there was a real problem, sort of like an idiot light of old, except now it's an idiot gauge. I wonder if the engine temp gauge runs this way?
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Old 08-26-2009, 04:25 PM   #16
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I was told by a Allison mechanic at a dealer that the transmission temperture should never be higher than the engine temperture. I have found that the engine usually remains the same while the Allison temps have a range.
Hugh
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Old 08-27-2009, 05:03 AM   #17
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Hush, I agree with the range. Usually never see my engine temp move around, but tranny temp will move when ascending or descending a hill, long hard pulls, and can even see it cooling off when the fan comes on.
I also have a boost gauge and a exhaust temp gauge, to see if I need to let off when putting a hard strain on the engine. When exhaust temp is up, tranny temp will rise, but never above 205.
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Old 08-27-2009, 06:01 AM   #18
Mudchief
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Mine does the same as Devildog.
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Old 08-27-2009, 06:50 AM   #19
KathyandDave
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205F is the max I've hit (displayed as 96C).
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Old 08-27-2009, 07:28 AM   #20
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You have a truck under warranty...why fool with it, take it to the dealer, let him fix it.
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