Transmission Stumble

[Tim907356]

My vehicle is a 2010 Yukon XL Denali with 129k miles. I think I'm the first one to tow with it, but we bought it used from a street lot, so don't know anything about its history. The hitch looked new when we first hooked up our 5000 lb. travel trailer. It's only been towed 3 times.
I'm on a long trip now, 550mi. away from home (no trailer on this one) but I noticed the transmission sort of stumbles when the engine first applies a load to it. For instance, I can be coasting downhill without pressure on the accelerator, at say 55mph. The tach would read 1300rpm's. When at the bottom, I first begin to apply pressure, the engine will rev to 1450-1500, and then lightly stumble until it fully engages, and the tach drops back to ~1350 or 1400. It happens on every occasion that the accelerator is applied; from stops, around corners, etc.
I just noticed this happening, so it may have been all along, and I haven't paid any attention. We have a long trip ~1400 miles, of pulling the trailer, so I wanted to know whether the transmission is good to the task, or if I should have it looked at immediately.
Thoughts?
Thanks.

 

[drakon543]

to your knowledge has the transmission ever been serviced? does the truck have the aux factory transcooler? should be able to see it through the grill or if you pop the hood and look infront of the radiator. a slight stumble like that i dont think your in any imminent cause for concern. however 5000lbs and if it doesn't have the transcooler could be heating up a bit much. also if you haven't had the transmission serviced i would have suggested to have it serviced a month prior to the trip.

 

[Tim907356]

It has the trans cooler, but the last time we pulled through the mountains of NC, it overheated to 240(max). The engine also overheated when this occurred. I’ve flushed the coolant, and have ordered a tru cool 40000, but it hasn’t arrived yet. I doubt the tranny has been serviced. Is that just a fluid and filter change? I thought I’d do that when the cooler arrived.

 

[swathdiver]

It has the trans cooler, but the last time we pulled through the mountains of NC, it overheated to 240(max). The engine also overheated when this occurred. I’ve flushed the coolant, and have ordered a tru cool 40000, but it hasn’t arrived yet. I doubt the tranny has been serviced. Is that just a fluid and filter change? I thought I’d do that when the cooler arrived.

The fluid should have been changed, especially after the high temp towing episode. The fluid is probably shot and has or will take out the transmission soon enough if not replaced.

If yours were mine, I'd whip out the Tech-2 and check out the transmission readings and maybe even run some diagnostic tests/functions. It may be time for the solenoids in the TECHM to be replaced.

 

[Tim907356]

No tech-2 but I’ll take it in.

 

[GreyStone]

If you enable tow/haul mode on the gear selector does it run any better/different?

 

[Tim907356]

Yes. It shifted earlier and stayed out of 6th. I used it in the hills, but it didn’t change the overheating situations with either the engine or tranny.

 

[swathdiver]

The engine overheats too huh? Well, that's a whole other diagnostic regime and one I would do first.

 

[Costal_Cat]

Yes. It shifted earlier and stayed out of 6th. I used it in the hills, but it didn’t change the overheating situations with either the engine or tranny.

Hey, so a couple of things for you do and or consider depending on your skill level.

I have a 2012 Denali XL and had very similar problems when I got mine towing my trailer. I would do these things some of which you can do yourself.

• Get the shop to do a new Tranny filter. This doesn't change all the fluid but it is a good start and the filter could use it. It is pain not having a drain plug so I let the shop do this.
• Install the TruCool. You need to take off the front bumper cover which is pretty easy. It can be tricky getting the new cooler in place as it is so much bigger. You have to watch the hose doesn't get pinched on the bottom of the cooler with the nipple attached. tricky but doable for most folks
• While it is out it is easy to run the rest of the fluid out bu having someone sit inside turn on and off the engine a few times into a 5-gallon bucket, refill of course
• Flush out the Radiator and replace

If you do all of that and it is not running cooler and shifting better than get a shop involved. Also, I never tow outside of tow mode. For me, with a 28ft trailer or boat, it will always hunt and peck between 5 & 6 and 5 feels like the RPMs are not right. In tow mode, I think it only goes to 4th and the little higher RPMS keeps everything flowing a little better and thus cooler. I live in NC and run a lot to the mountains and down to FL. Before doing the above, and new rear shocks, I was having the same issue. Now it runs a cool 190 at the worst and under on the worst day with the AC on. Without towing on a hot day it really never goes above 150 now.

 

[Tim907356]

I just returned from MD to SC: 550mi., not towing, and the stumbling condition did not change for better or worse. Max temp was 172. I have a tm cooler coming so I’ll prob do the cooler, fluid and filter at the same time. I already flushed and replaced coolant.

I’m thinking about mounting the cooler below the bumper behind the lower grill, in clean air. It would lower the thermal load on all three systems. Any thoughts?

 

[BG1988]

I just returned from MD to SC: 550mi., not towing, and the stumbling condition did not change for better or worse. Max temp was 172. I have a tm cooler coming so I’ll prob do the cooler, fluid and filter at the same time. I already flushed and replaced coolant.

I’m thinking about mounting the cooler below the bumper behind the lower grill, in clean air. It would lower the thermal load on all three systems. Any thoughts?

check the air filter, a clogged one can cause transmission issues check the MAF/IAT/MAP(if equipped) make sure it's correct readings

 

[Tim907356]

Just an update; here's some pics of the installation. I cut through the plastic fascia behind the lower grill, and the lower bumper extension to create airflow. The cooler (tru cool 30k) mounted behind that. It's not plumbed in yet, as I didn't have any trans. fluid, but will be getting some today.

 

[Tim907356]

How do you know which transmission cooler line is the send line, and which is the return line???

 

[donjetman]

It goes from the tranny, thru the radiator first, then the cooler, then back to the tranny.

 

[Tim907356]

After the cooler install, I took it in for tranny service; change fluid/filter, and diagnosis. He said it all checked out fine. But then after some direct questions about the stumble, and overheating, he said the torque converter was going out; a common problem (at 130k??). He asked if I felt the 'little flutter' when it engages, which of course is my 'stumble', so yes. He also said the overheating was due to the torque converter wear.

$1700 was offered as the cost to replace the t.c. But also, if I let it go too long or pulled the trailer a long way, it would ruin the tranny and I'd be looking at double that for a rebuilt unit.
Thoughts on this info. and proposal?

 

[thompsoj22]

After the cooler install, I took it in for tranny service; change fluid/filter, and diagnosis. He said it all checked out fine. But then after some direct questions about the stumble, and overheating, he said the torque converter was going out; a common problem (at 130k??). He asked if I felt the 'little flutter' when it engages, which of course is my 'stumble', so yes. He also said the overheating was due to the torque converter wear.

$1700 was offered as the cost to replace the t.c. But also, if I let it go too long or pulled the trailer a long way, it would ruin the tranny and I'd be looking at double that for a rebuilt unit.
Thoughts on this info. and proposal?

Even if he is a highly experienced trans specialist his prognosis is a "guess" at a cost of $1700 of your vacation dollars. You are towing at close to max weight, Add a headwind and your relaxing RV road trip becomes a 3300 rpm 6 mpg white knuckler "are we there yet?" Just get out there, take your time, climb the grades at 45 mph in 4th and stay to the right with the big rigs. The hill will end and down the road you go. There is another forum member that did replace only the convertor on his trans but he did it himself in conjunction with rear main seal/pickup tube o ring. I would not advise doing it now, Take your trip and hope for the best. We also tow, It is ******* our 08 xl-1500 6.2, 143,000 miles our TT is 4300 lbs loaded and we average 8 mpg. Each time we "hitch up/load up" the little voice in the back of my mind is saying "hotel/restaurant". Im rambling, Maybe an aftermarket extended warranty would give you peace of mind on road trips?

 

[1BADI5]

Remember this tech tip gents......... Maintenance is always cheaper then repairs.

Blow a trans on vacation.........you've at best just tripled the cost of you repair.

 

[Rocket Man]

After the cooler install, I took it in for tranny service; change fluid/filter, and diagnosis. He said it all checked out fine. But then after some direct questions about the stumble, and overheating, he said the torque converter was going out; a common problem (at 130k??). He asked if I felt the 'little flutter' when it engages, which of course is my 'stumble', so yes. He also said the overheating was due to the torque converter wear.

$1700 was offered as the cost to replace the t.c. But also, if I let it go too long or pulled the trailer a long way, it would ruin the tranny and I'd be looking at double that for a rebuilt unit.
Thoughts on this info. and proposal?

I would call around for a few quotes before settling on that price but it does sound like the shop is probably right. And like others have said, if you would have had the trans serviced regularly you probably wouldn’t be in this position. I definitely wouldn’t be going on any long trips until you get it fixed. If it goes out when you’re a thousand miles from home the shop you get it towed to will surely rake you over the coals due to your dire situation.

 

[Tim907356]

Well, after all the overheating was solved (a while ago,,,I know!) I just got back from Cincinatti, where the temps were 0-10deg. I came back during that snow event that shut down I-95, but cleanly, at least, down I-75.
When I did the transmission cooler installation, I did not put the thermostat in, partly because of issues with the shop I got it from. Now, I've got one in hand due to the cold temps I didn't anticipate. The TX never made it to 100deg. F. Im heading back tomorrow, and was going to install it today. However, knowing the flow direction is now critical!!
SO, some say it comes out of the TX lower port, some say the upper port. Earlier, donjetman said it comes from the TX, to the radiator, to the aux cooler, back to the tx. If this is the case, it comes from the upper TX port, and goes to the lower radiator port. This is opposite of most comments I've read, stating the lower TX port is the send.
Can anyone confirm this???

 

[Geotrash]

Well, after all the overheating was solved (a while ago,,,I know!) I just got back from Cincinatti, where the temps were 0-10deg. I came back during that snow event that shut down I-95, but cleanly, at least, down I-75.
When I did the transmission cooler installation, I did not put the thermostat in, partly because of issues with the shop I got it from. Now, I've got one in hand due to the cold temps I didn't anticipate. The TX never made it to 100deg. F. Im heading back tomorrow, and was going to install it today. However, knowing the flow direction is now critical!!
SO, some say it comes out of the TX lower port, some say the upper port. Earlier, donjetman said it comes from the TX, to the radiator, to the aux cooler, back to the tx. If this is the case, it comes from the upper TX port, and goes to the lower radiator port. This is opposite of most comments I've read, stating the lower TX port is the send.
Can anyone confirm this???

@donjetman is spot on about the flow order. And, it flows from the transmission into the bottom of the radiator fluid cooler, and out the top of it to the aux transmission cooler, then back to the transmission.

Also, I missed your earlier posts about the recommendation you received from the shop about the TC, and I think they're right. I replaced the TC in my 2012 XL Denali proactively (I had a good transmission shop do it), and he said that the lockup clutch was really worn (at 120K), which is the problem that can take out the transmission when it finally goes because it sends shrapnel through the pump and valve body. So in my opinion, that is a wise upgrade to make proactively. The whole job was around $1400 out-the-door, including an upgraded TC with a billet cover and stronger lock-up clutch, new rear main seal since they had the transmission out anyway, new fluid and filter. I went with a CVC BU60-FHD torque converter on the shop's recommendation.