Transmission possibly slipping

[durbancic]

2011 Yukon Denali xl. 157k. Bought last year w/ 149k. Bought this as 3rd vehicle to mainly haul 21' TT we purchased last year. Don't drive it weekly, typically. Transmission cooler lines were replaced last year before I purchased it.
Went camping to MI towing 4500lb TT a couple weeks ago. Towing went well. I think the transmission temp only got up to 219 max on the trip. While we were on the trip the fuel sending unit sprung a leak for a few days before getting it fixed. Not much, if any towing while the leak was going on. While the leak was going on we were on a scenic drive, traveling around 15-25 mph up and down winding roads. Transmission was clunky at times. Attributed it to lack of fuel / pressure. Shifted into tow mode and it improved it a bit. Got the sending unit replaced and watched while they did it. Dropped the drive shaft, fuel tank, etc..
Continued on the trip towing further up north then back home to Ohio. No real issues.
However, I have noticed some things that *might* not have been going on before the trip.
- when driving and coming to a stop occasionally it will clunk a bit downshifting
- when traveling around 40mph coasting, foot off the gas, around 1000rpm and then hit the gas the tach will jump to like 15-1600 then drop down to 12-1300. Is the transmission slipping, or did I never notice this before?
- the transmission acts clunker than it did before
While towing I wasn't going crazy. Kept it in tow mode, M5 about 95% of the time. Didn't go above 70 90% of the time (was too concerned about the 8mpg I was getting!)

One other thing to note. I have noticed a faint Coolant smell the past month or so. Seems to be coming into the cab. Have added Coolant a few times to the reservoir. About 1/2-1" at a time. No noticeable leak anywhere though. Just inspected the engine tonight and there is a wet / greasy spot on the engine front, above and behind the lower pulley that has the 2 belts connected to it. (ac/and main serp. Belt). Could not smell Coolant on the residue. More dark and oily.
Could I have some pieces of the rusty fuel line clogged in an injector?

 

[the highlander]

I would do a trans learn first, or albeit do the service for the trans and then do the learn.

 

[B-train]

I have owned 2007, 8, 9, and 17 Denali trucks. All of the older generation (07-14) seem to have driveline clunks as they get higher up in mileage. I've done everything short of replacing driveline components and it's always there. I just keep up on good fluid maintenance andcorrect (matched) tire size.

My 2008 usually does its clunking on an aggressive downshif while passing. It has also done it when downshifting, and in tow/haul. My speculation is some slop in the driveline from 170k miles and possibly weak or worn clutches in the transfer case for the AWD system. Service both differentials and the transfer case. Dextron6 in t-case. A good full synthetic in the axles.

The revving up after coasting may just be as simple as the TCC unlocking and then settling back into a gear. Would probably have to drive it for a better feel of the situation though.

Coolant smell could be from the plastic T fittings by the water pump area. Also, check the crossover tube right under the throttle body (attaches to both cylinder heads) for corrosion.

 

[Doubeleive]

well first off you have a couple issue's going on
1. what is a fuel sending unit and how does it spring a leak? (I assume you mean fuel pump) but not quite sure how it springs a leak.......that sounds like a death trap
2. the torque converter on the 6l80's go bad and your issue sounds exactly like what is happening, eventually they take the rest of the transmission with it. at minimum you most likely need a rebuild. I would recommend finding the best transmission shop in town and have them take a look at it.
3. coolant doesn't just evaporate, you have a leak somewhere keep looking small leaks can be hard to find you need a flashlight and a tilt mirror, you need to look from the bottom up, not top down. although you should look at the radiator all over front, back, sides. this may mean you need to unbolt it and pull it back some, but I would check all other locations thoroughly first before having to do that.
if you absolutely cannot find a coolant leak then you need to do a block test and pressure test. but only after you have made absolutely sure there is no external leak.

 

[Doubeleive]

I have owned 2007, 8, 9, and 17 Denali trucks. All of the older generation (07-14) seem to have driveline clunks as they get higher up in mileage. I've done everything short of replacing driveline components and it's always there. I just keep up on good fluid maintenance andcorrect (matched) tire size.

My 2008 usually does its clunking on an aggressive downshif while passing. It has also done it when downshifting, and in tow/haul. My speculation is some slop in the driveline from 170k miles and possibly weak or worn clutches in the transfer case for the AWD system. Service both differentials and the transfer case. Dextron6 in t-case. A good full synthetic in the axles.

The revving up after coasting may just be as simple as the TCC unlocking and then settling back into a gear. Would probably have to drive it for a better feel of the situation though.

Coolant smell could be from the plastic T fittings by the water pump area. Also, check the crossover tube right under the throttle body (attaches to both cylinder heads) for corrosion.

a few things can cause clunking besides the normal clunk.
1. the motor mounts are liquid filled and are notorious for tearing and the liquid spills out and they will cause clunking, there are ways to check and the fix is to put hummer mounts (solid rubber) one time fix and they never have to be done again.
2. slip yoke if not lubed properly will make a clunk
3. front differential mounts, the rubber breaks down and they just clunk like heck.
I have done all of the above and I get no clunk, she runs like you bit her in the @ss, I may on a rare occasion get a trans clunk if I make it do it by gassing it and letting off real fast before it gets a chance to decide what to do, but no drivetrain related clunk otherwise.
there is some light inherent clunk you may hear when parked on a incline and shifting out or when initially shifting even on a level surface because there is always some light play in the driveline/transfer case unless it is bound up from weight of a incline or parked against a obstacle in which case you make get a louder clunk.
other sources could be sway bar bushings or end links, maybe a body mount but those typically occur specifically when turning or going over a bump or in/out of a driveway.

 

[durbancic]

I have owned 2007, 8, 9, and 17 Denali trucks. All of the older generation (07-14) seem to have driveline clunks as they get higher up in mileage. I've done everything short of replacing driveline components and it's always there. I just keep up on good fluid maintenance andcorrect (matched) tire size.

My 2008 usually does its clunking on an aggressive downshif while passing. It has also done it when downshifting, and in tow/haul. My speculation is some slop in the driveline from 170k miles and possibly weak or worn clutches in the transfer case for the AWD system. Service both differentials and the transfer case. Dextron6 in t-case. A good full synthetic in the axles.

The revving up after coasting may just be as simple as the TCC unlocking and then settling back into a gear. Would probably have to drive it for a better feel of the situation though.

Coolant smell could be from the plastic T fittings by the water pump area. Also, check the crossover tube right under the throttle body (attaches to both cylinder heads) for corrosion.

Thank you for the reply. The coolant smell is indeed one of the T fittings. I ordered it and it is ready to be installed. I have been holding off because I am worried about opening up the coolant system. Do I need to worry about getting air in the system when I do this? Do I simply remove the old fitting and install the new? Then top off the reservoir to replace whatever was lost? I just remember my friend in HS got air in his new engine he put in a jeep and it overheated. I'm probably just being paranoid.

 

[durbancic]

well first off you have a couple issue's going on
1. what is a fuel sending unit and how does it spring a leak? (I assume you mean fuel pump) but not quite sure how it springs a leak.......that sounds like a death trap
2. the torque converter on the 6l80's go bad and your issue sounds exactly like what is happening, eventually they take the rest of the transmission with it. at minimum you most likely need a rebuild. I would recommend finding the best transmission shop in town and have them take a look at it.
3. coolant doesn't just evaporate, you have a leak somewhere keep looking small leaks can be hard to find you need a flashlight and a tilt mirror, you need to look from the bottom up, not top down. although you should look at the radiator all over front, back, sides. this may mean you need to unbolt it and pull it back some, but I would check all other locations thoroughly first before having to do that.
if you absolutely cannot find a coolant leak then you need to do a block test and pressure test. but only after you have made absolutely sure there is no external leak.

The fuel sending unit is the fuel pump. Just the official name for it. The 2 steel lines that come out of the top of the unit in the gas tank were rusty and had a small leak.
I will get it into a transmission shop to have them check out the transmission.
Coolant leak was found to be one of the T fittings at the firewall. Just need to replace it now.

Thank you for all your replies everyone. I thought after 6 weeks of no answers that this was going to be a dead thread!

 

[donjetman]

When my heater hose T-fitting broke, replaced both with www. gruvenparts.com metal Ts.

 

[B-train]

When you do your coolant repair, you will probably lose a lot of what's in the system. Depending on age, it may be good to just drop as much as will come out and refresh it.

When you fill the system, leave the cap off and start the motor once the over-flow jug is at a safe level (I usually do between cold and hot for burping). Watch the temp gauge and if you have an IR temp gun, you can also monitor temps near the water pump, heads, etc. Not really necessary but helps. I usually massage the upper hose from the water pump outlet up to the radiator by squeezing it a good number of times. This will push air up the hose and into the radiator and just helps move air through the system.

After running for a bit, make sure the temp gauge seems to read correctly. I've had ones that need a heat-soak cycle with the engine off for a short time to heat up the area by the t-stat if there's air stuck there. You can also just put a hand on the upper hose and see where the heat is - stuck at the water pump, or is the whole thing heating up.

Once you see operating temp, the over-flow jug should be hot to the touch as well (cap off this whole time). Top off as needed and cap on with motor off. I like to cap it when hot, so it pulls a vacuum on the system as it cools, then expands back to where it was when hot - prevents unnecessary pressure on the system IMO.

 

[B-train]

When my heater hose T-fitting broke, replaced both with www. gruvenparts.com metal Ts. View attachment 381987

Can't go wrong with silicone hose!! I've used hundreds of feet of that stuff over the years on generators and it is really indestructible. Super easy to work with as well