Low trans temps

LTZNewb said:

Hi all, this is only my second post and I’m stumped with as to what’s going on. I have a 2011 Tahoe LTZ with the 6L80 trans. I hear a low pitch humming when driving. It’s usually more noticeable between 20-40mph. Sometimes it’s more noticeable between 5-15 mph. Nevertheless, I hear it almost all the time at highway speeds. It’s shifting smoothly, doesn’t seem to be slipping at all, rpm’s are at 1700-1800 @ 70mph, and idles fairly smoothly. I’ve checked my front hubs and they’re all tight. It’s not tire noise. What I’ve been noticing in trying to track this humming down, is that my trans temp never gets anywhere near operating temps. The highest continuous temp I’ve read is 126. Only one time has it reached 156. Most of the time it’s around 115, and that’s with driving some interstate and some in town for an hour or more. I’ve checked my fluid level multiple times hot, and it appears to be at the top of the crosshatch even though the temps are lower than they should be. I’m wondering if:
A. Is there an actual temp sensor, and if so, could it be faulty? I can’t seem to find out anywhere if there even is one.
B. Is there a thermostat that regulates the flow between the trans and the cooler, and could it be stuck open?
C. Am I damaging my trans by driving with too cool of temps?
I just bought this in July with 178k, and am currently sitting at 193k. I just don’t want to grenade my trans.
Any thoughts would be much appreciated. Thanks!

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Doubeleive said:

Those are pretty good temps in my book, some may disagree but heat kills. Have you looked to see if it has a external transmission cooler?s such as a trucool? The gmt 900's do not have a thermostat like the later models so no nothing would be stuck open. Humming could be several things but the ring-n-pinion is a usual suspect, as well as u joints or rear diff. Maybe even the transfer case if equipped

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LTZNewb said:

EDIT: I forgot to mention that there are no leaks, and I had the fluid and filter changed 3k miles ago, and the fluid is not exactly red but is translucent.

Thanks for responding. It has an external cooler, and have not seen any leaks. I changed out oil in both diffs and transfer case about 5k ago. I hear the humming less when the temp gets the hottest, which isn’t often. I’ve read that the TC’s are notorious for failing at high mileage, and just want to catch any possible damage early so I don’t grenade my transmission. I wanted to get the forum’s thoughts before I inquire at the transmission shop. Thanks

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j91z28d1 said:

nosies like this are hard to pin people.

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Doubeleive said:

Have you checked the front wheel hubs? At 178k its likey the front hubs would be at end of life, just something to consider as well. Average hub life is 160k

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LTZNewb said:

Hi all, this is only my second post and I’m stumped with as to what’s going on. I have a 2011 Tahoe LTZ with the 6L80 trans. I hear a low pitch humming when driving. It’s usually more noticeable between 20-40mph. Sometimes it’s more noticeable between 5-15 mph. Nevertheless, I hear it almost all the time at highway speeds. It’s shifting smoothly, doesn’t seem to be slipping at all, rpm’s are at 1700-1800 @ 70mph, and idles fairly smoothly. I’ve checked my front hubs and they’re all tight. It’s not tire noise. What I’ve been noticing in trying to track this humming down, is that my trans temp never gets anywhere near operating temps. The highest continuous temp I’ve read is 126. Only one time has it reached 156. Most of the time it’s around 115, and that’s with driving some interstate and some in town for an hour or more. I’ve checked my fluid level multiple times hot, and it appears to be at the top of the crosshatch even though the temps are lower than they should be. I’m wondering if:
A. Is there an actual temp sensor, and if so, could it be faulty? I can’t seem to find out anywhere if there even is one.
B. Is there a thermostat that regulates the flow between the trans and the cooler, and could it be stuck open?
C. Am I damaging my trans by driving with too cool of temps?
I just bought this in July with 178k, and am currently sitting at 193k. I just don’t want to grenade my trans.
Any thoughts would be much appreciated. Thanks!

Click to expand...

Joseph Garcia said:

Get the truck to a local shop and put it on a lift where you can get the truck in the air and all 4 wheeles off the ground/lift platform. Have 1 person in the truck and put it in drive and get up to the speeds that you are noticing the sound. Then, have a second person with a mechanics stethoscope listen to all of the drive train parts, one at a time, until the noise is isolated.

I had a similar noise, and using the method indicated above, the shop was able to locate the sound in my front differential. We replaced the front differential with a low mileage used one, and the sound was gone forever.

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j91z28d1 said:

next time you get it humming, pop the tranny in neutral and see what happens. does the sound change with vehicle speed or engine revs. give it some throttle while in neutral as well and see if the noise follows engine rpm or. not.

nosies like this are hard to pin people.

Click to expand...

Joseph Garcia said:

Get the truck to a local shop and put it on a lift where you can get the truck in the air and all 4 wheeles off the ground/lift platform. Have 1 person in the truck and put it in drive and get up to the speeds that you are noticing the sound. Then, have a second person with a mechanics stethoscope listen to all of the drive train parts, one at a time, until the noise is isolated.

I had a similar noise, and using the method indicated above, the shop was able to locate the sound in my front differential. We replaced the front differential with a low mileage used one, and the sound was gone forever.

Click to expand...