View Full Version : Transmission Trouble ??
I was pulling my travel trailer (10K loaded) up a moderate grade using tow haul a week ago when all of a sudden the transmission downshifted with a bang into 3rd gear and the check engine light came on. I continued up the grade in 3rd gear and pulled over at the top. Trans fluid was okay and was only 170 degrees when the downshift occurred. Finding nothing wrong I cycled the key a few times and pulled back out onto the highway. (With 1000 miles to go) The worry some part is the transmission had not downshifted back to low gear when I stopped and it started out from a dead stop in 3rd gear. Easing it along I drove a few miles (still locked in 3rd gear) keeping rpm around 2200 and transmission temperature under 200 degrees. After driving about 30 miles in this condition I found a large parking lot and pulled into it. Again fluid level was a little higher but not over the full mark. I again cycled the key about 5-6 times, but let the truck sit for about 20 minutes. This time when I pulled back out on the highway the transmission shifted normally and started out in 1st gear, but the check engine light was still on. After an overnight stop, the next day the check engine light was OFF and the transmission shifted normally for the rest of the trip home.......Trans sump fluid and filter were changed 5k before this occurred. 152K on transmission.......Any idea what happened. Shift solenoid ??
DmaxMaverick
10-09-2015, 20:52
The 3rd gear lock was limp mode. Something was amiss to cause that. Are you using any power-adder (Edge, etc.)? What you described is the same as when I get an overboost or tranny slip. You need to read the code to know what it was. It will remain in history for a while, even if the SES lamp isn't on. Most simple code readers will only show P0700 if it's a TCM code (which only means there is a DTC in the TCM, and it commands the MIL/SES). You'll need a more sophisticated scanner (Tech II, Snap-On) to read the TCM. Most modern shops will have one.
I have an Edge EZ (kept in #1) that's been on the truck for 125K miles. I never thought to look at my ISO boost gauge when it happened and I do have a Kennedy Boost stick, although I have pulled many steeper grades than the one on which the fault occurred. I don't own an OBD II, but will buy one even if it's for a future occurrence.
maverick_935
10-10-2015, 07:37
long story but when mine did that i put it in to the tranny shop and the end result was the torque converrter had failed. apparently common on the 05's
a5150nut
10-10-2015, 11:52
Roy, Does your Edge read your engine/trans codes?
It is unfortunate, but these boxes with "slip protect" seem to have a tendency to degrade the transmission's holding capacity over time. I have also found that with the Boost Stick added the power increases significantly so I suggest that you back down the Edge at least one power level.
My Edge EZ is already operating on #1 (the lowest level out of three).
Last one that I dealt with that had this combo and this issue we went to my 50HP tow tune direct in the ECM and he's been tickled pink ever since.
More Power
10-12-2015, 14:29
I'd want the code(s) before doing anything.
I have an appointment with a Tech II Tuesday morning.
The Tech II scan tool showed a TCM PO735 fault (Gear 5 incorrect ratio). The technician and I agreed that unless it does it consistently that we could be chasing goblins. I have pulled a 10K trailer 1000 miles since the fault occurred. Next trip is to Talladega, so we'll see what happens then.
P0735 is the slip in 5th gear that is common when the transmission's capacity is tested/overcome. It will very likely do it again and it will get worse the more that it happens. It's kind of a death by 1000 paper cuts deal.
DmaxMaverick
10-13-2015, 09:55
It slipped in OD. Edge + stick + (load conditions) allowed that to happen. Simple as that, and not a goblin. Either lock out OD or downgrade the power enhancers the next time you have a similar load on a similar grade. It's very likely that if you repeat the conditions, you'll repeat the result. Each slip gets more likely (the next time), at lesser loads.
Funny thing is, when working directly in the ECM we can make it more responsive, pull stronger, run cooler and still not limp the trans. There's something about the way the fueling comes on (delay then rush) and the fact that the ECM is not in direct control of it that tends to get under the Allison's skin.
Locking out overdrive when pulling even a slight grade makes sense. Thinking back to the conditions when the fault first appeared, it was probably a 5% grade, but I had lugged 5th gear down to 55 mph (just before tow haul would have caused a downshift) while pulling the 10K lb travel trailer. I'm hoping the fault won't reappear when driving unloaded.........Thanks for all the assistance in working this thing out.
The reason my 2006 is bone stock and staying that way. It tows plenty strong for me and gets 12.0 +/- 0.5 mpg towing my fifth wheel. When not towing at a steady 62 mph it gets 21.5 and has 155,000 on the odo.
I'm a happy camper and heading to Talladega next Wednesday.
We'll be in site 807. Stop by,
So you are in West Park B?
I will be in East Park, but I don't know the site # yet. I am a Shriner and will be doing some volunteering while there. We will be driving around on golf carts transporting fans that have problems walking distances. I should know my site # in couple of days.
When are you arriving? I will get there at noon'ish on 10-21, but will be on the night shift for the first couple of nights.
I'm in Geico Green in the infield between turns 3 and 4. We'll be arriving 5pm Wednesday.
I will definitely see you then. I will be helping work the north tunnel entrance to the infield starting Wednesday evening. I'll make sure I stop by. I will be just outside turn three, but I don't know my site number yet.
Locking out overdrive when pulling even a slight grade makes sense. Thinking back to the conditions when the fault first appeared, it was probably a 5% grade, but I had lugged 5th gear down to 55 mph (just before tow haul would have caused a downshift) while pulling the 10K lb travel trailer. I'm hoping the fault won't reappear when driving unloaded.........Thanks for all the assistance in working this thing out.
I would not expect it to happen unloaded, BUT some have reported this when pulling out to pass at around 60 mph.
DmaxMaverick
10-15-2015, 08:56
I would not expect it to happen unloaded, BUT some have reported this when pulling out to pass at around 60 mph.
I've seen this as well, but only with cruise engaged. The delayed downshift allows it to stay in OD long enough to get overrun when the boost comes up quickly, before ground speed increases. It happens very quickly. To prevent this, disable cruise and let it downshift (or downshift manually) for passing-type situations.
Thanks for the warning /advice. Actually I drive like an old fart and can't remember the last time I hit passing gear. I have enough power that a downshift really isn't necessary when passing. I'm hoping that after the fault resolved itself and I continued to drive another 1000 miles under load without a repeat occurrence that maybe I had encountered "the perfect storm" when I lugged overdrive.
DmaxMaverick
10-15-2015, 14:30
Thanks for the warning /advice. Actually I drive like an old fart and can't remember the last time I hit passing gear. I have enough power that a downshift really isn't necessary when passing. I'm hoping that after the fault resolved itself and I continued to drive another 1000 miles under load without a repeat occurrence that maybe I had encountered "the perfect storm" when I lugged overdrive.
This is the primary contributor, even if once in a while. If you are loaded and need to speed up, for passing or whatever, force or let it downshift. Although the power may be greater at higher RPM's, and the shaft-torque is about the same, the torque-distance is less, as the same torque is spread over the higher RPM's. This, for the same reason Diesels use up gasser trannies. Even though they may have similar HP and TQ ratings, the Diesel is doing it with about 1/2 the shaft rotations. This results in near double the input torque, per revolution.
Add to that, with the TCM adaptive learn process, lazy old fart driving may make the TCM a little slow on the uptake when you do lay on it out of the blue. Perhaps the last piece of the perfect storm puzzle.
When towing on the interstate, I set the cruise control on 60 mph and plug along. Question: At that towing speed do you think I'd be better off locking out overdrive and living with the increased rpm and reduced fuel mileage or just permanently remove the power adders ?? Tow haul of course.
rapidoxidationman
10-16-2015, 08:49
IIRC 65mph in overdrive puts my engine at its happy place for torque and efficiency of 1900rpm (best mileage too). If your gear ratios are similar, maybe bump up 5mph and see what happens?
Or just set your speed to whatever spins the engine at 1900....
DmaxMaverick
10-16-2015, 10:03
I do not recommend locking out OD with that load at that speed. I only suggest allowing it to downshift when you hit a grade, then engage OD once it's behind you. Nothing wrong with leaving the power adders in, but the additional power will require a little more attention to keep everything happy. I do the same, with 2-4K more in tow, quite a bit more power, and a taller gear ratio (33" tires), still on the (healthy) OEM tranny. I still get an occasional overboost, but that's my fault for letting it get there. Almost everywhere I go (camping) requires 7%+ grades, and none are a problem unless my attention wanders.
Yes, we have traveled the Rocky Mountains occasionally (live in Florida) and have pulled some of those 7% 5 mile long grades with this truck as outfitted. It's hard not getting a small grin when passing 18 wheelers and motorhomes in the slow lane.
I think I now have a pretty good grasp on how to handle this situation in the future. Many thanks to you and John Kennedy for all your advice.
Roy Wires
Question: At that towing speed do you think I'd be better off locking out overdrive and living with the increased rpm and reduced fuel mileage ...Tow haul of course.
please excuse the nube question, but with my '04 I thought being in tow/haul gave me overdrive lockout by default? if not, how would I do it, when, and why? many thanks.
I can't speak for the '04 models, but on my '05, you push the tow haul button in and hold it in for a second or two, and it locks out overdrive. An additional icon will appear on the dash next to the tow haul icon indicating overdrive lockout is selected. Regarding when to use it........I would refer you to all the comments from Dmax Maverick and John Kennedy in this thread.
thx.
so using tow/haul then only modifies shift points? and requires an additional action on the same button locks out OD?
(times like these I wish I could get a hold of the "diesel supplement" that didnt come with my used truck purchase)
rapidoxidationman
10-17-2015, 19:06
Didn't jbplock send you a copy of his? Unless you have a later '04(LLY, it should be virtually identical to the '03(LB7?)...
At any rate, I'm pretty sure the operation of the tow/haul and OD switch is covered in the plain old owner's manual - not the diesel supplement. The Allison transmission is also used on the 8.1L gasser.
DmaxMaverick
10-18-2015, 00:43
thx.
so using tow/haul then only modifies shift points? and requires an additional action on the same button locks out OD?
(times like these I wish I could get a hold of the "diesel supplement" that didnt come with my used truck purchase)
With 2003 and later models, the T/H and OD lockout are a function of the button at the end of the selector stalk (shifter). Previous models require a wired-in mod and a switch.
T/H only modifies the shift points and torque converter engagements. It does not inhibit OD, but it does delay OD engagement during normal driving.
Didn't jbplock send you a copy of his?
crap, yes, found it filed in unintuitive location on computer
thx for the reminder :-)
and it turns out there wasnt anything there about tow/haul as you surmised, its all in basic manual; duh on me.
a5150nut
10-18-2015, 11:37
I sure like the TH mode on my 06. Use it to descend hills and additional slowing when needed. Or once in a while to confuse some idiot that has to ride my bumper.
Reminds me of the 7 speed autos used in CAT scrapers.
I will be putting my '06 to work tomorrow morning. Heading to Talladega for a few days for some racing and crowd watching.
I'm close enough it it is only 95 miles, but still good to get off of this home base site for a few days.
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