Tranmsission Problem????

[LJPinDrakeND]

We bought our 2010 Tahoe used in September of 2012. All things considered, we love the truck. Even some of it's quirks I can get used to or just ignore. But this one is worrying me.

In early April, I took it to the dealer and had many of the 60K checks done, including a tranny service, along with the recall for the dipstick tube. The tranny seemed much better and quite a bit smoother in all aspects of opertation.

The other day, I was driving it on a straight flat stretch of Hwy 50 in Dayton NV. I had just accelerated from a stop light and had reached my desired speed of 40MPH. I set the cruise control (I use cruise all the time to avoid getting tickets) and the transmission had the trailering option engaged. In other words, the dash light was ON showing that system was operating (I use it when going down hills with cruise control to hold the desired speed).

All of a sudden, the engine tached up to over 3500 RPMs and I could feel a slight "grinding" and also heard a momentary grinding noise with the feeling. The vehicle speed did NOT change with the higher RPM nor did I feel any gear shifting.

I disengaged the cruise control, coasted for a couple of seconds, then brought it back up to speed. This did NOT re-occur.

Now, over the past several days, I've noticed the transmission to be a bit sluggish from stoplights and have to press the gas pedal down a bit further to get it to downshift when accelerating to highway speeds. Even still, it seems sluggish like there is something holding it back. This truck has always been great on merging into traffic and leaps like a jackrabbit on crack from stoplights when pushed to do it.

I've also noticed that the transmission temp is riding a bit higher than it used to. It would climb to 180 or 200 if hauling butt up a hill on I-80 over the Sierras, but not on the flats where we live. Now, that's where it's riding.

So, all this is starting to make me think tranny problem, but with all the computer controls, I can't help but wonder if there's a chance something else is causing all this.

Thoughts?

 

[TheFuzz]

So a few weeks after a transmission service, you heard a grinding noise as the truck slipped out of gear, and have noticed higher temps and problems shifting/accelerating...yet you are still driving the truck around?

Take the it back to the dealership! Grinding is not caused by the computer. Go get it looked at pronto. If something is jacked up and you catch it in time, the faulty part can usually be pulled and replaced. If there are pieces of metal circulating in your trans fluid and you keep driving the truck (thereby allowing those bits of metal to circulate through the whole transmission), its only a matter of time before the whole thing grenades.

 

[LJPinDrakeND]

I don't know if I was specific enough. The grinding is not continuous. It was a momentary sound with the grinding feel when the RPM spiked.

Again, the noise was momentary in nature.

The temps on the other hand are new and constant.

No, I know enough to have it towed back if the thing was grinding all the time.

 

[TheFuzz]

I understood your original post. Whether the grinding is constant or not doesn't matter; the fact that you experienced a grinding noise while the transmission was under load, combined with an RPM spike indicating gear slippage, leads me to believe that something let go in the trans (possibly a planetary gear tooth or clutch pack). There are magnets on the pan that may have caught any large pieces, but the increased temps and sluggish shifting make me think that you have clutch material or metal shards clogging up your fluid passages.

Again, get it into the shop. I might be wrong, but if I'm right then you are only risking more damage by waiting.

 

[InTruckDesign]

I would bet that your throttle body is dirty or the tps is starting to go. Most of the ones I personally know about had it happen when on cruise, out of nowhere it happens. Ends up being a tps issue where the actual vs. reported throttle correlation is off ie. not the same. And before you think that the throttle body cannot affect the transmissions normal functions, think again, lots of people have had driveability issues and thought it was trans related and it ended up being a throttle body/tps issue.

http://www.tahoeyukonforum.com/forum/showthread.php?t=47665

 

[TheFuzz]

He mentioned a grinding noise, and subsequently noticed other problems. On my NBS Yukon, I cleaned the throttle body but forgot to plug the MAF sensor back in, and it maxed out the line pressure in the trans to compensate. It felt like a race transmission...the shifts were jarring, even at low speed. So yes, I agree that TB/intake problems can cause transmission performance irregularities, but the grinding noise, shifting issues and increased temps point toward a little more than a dirty throttle body or bad TPS sensor.

Our thoughts and opinions don't really matter though. He needs to get the truck looked at. I would be interested to know what the final verdict ends up being. Hopefully it truly is something simple...transmission problems are a crappy thing to be stuck with.

 

[GM Customer Service]

We bought our 2010 Tahoe used in September of 2012. All things considered, we love the truck. Even some of it's quirks I can get used to or just ignore. But this one is worrying me.

In early April, I took it to the dealer and had many of the 60K checks done, including a tranny service, along with the recall for the dipstick tube. The tranny seemed much better and quite a bit smoother in all aspects of opertation.

The other day, I was driving it on a straight flat stretch of Hwy 50 in Dayton NV. I had just accelerated from a stop light and had reached my desired speed of 40MPH. I set the cruise control (I use cruise all the time to avoid getting tickets) and the transmission had the trailering option engaged. In other words, the dash light was ON showing that system was operating (I use it when going down hills with cruise control to hold the desired speed).

All of a sudden, the engine tached up to over 3500 RPMs and I could feel a slight "grinding" and also heard a momentary grinding noise with the feeling. The vehicle speed did NOT change with the higher RPM nor did I feel any gear shifting.

I disengaged the cruise control, coasted for a couple of seconds, then brought it back up to speed. This did NOT re-occur.

Now, over the past several days, I've noticed the transmission to be a bit sluggish from stoplights and have to press the gas pedal down a bit further to get it to downshift when accelerating to highway speeds. Even still, it seems sluggish like there is something holding it back. This truck has always been great on merging into traffic and leaps like a jackrabbit on crack from stoplights when pushed to do it.

I've also noticed that the transmission temp is riding a bit higher than it used to. It would climb to 180 or 200 if hauling butt up a hill on I-80 over the Sierras, but not on the flats where we live. Now, that's where it's riding.

So, all this is starting to make me think tranny problem, but with all the computer controls, I can't help but wonder if there's a chance something else is causing all this.

Thoughts?

Hey there,

I understand that you feel frustrated that you cannot figure out what is causing the issue with your Tahoe. I am interested in hearing more details about your concern and your dealership experience. Please private message me the details.

Safe travels,

Jennifer T.,
GM Customer Care

 

[LJPinDrakeND]

I can understand completely how a supposedly unrelated system can and will affect something else. I've never seen a vehicle more tied into computers than these.

I'm an accomplished shade-tree mechanic type but I don't mess with transmissions other than to remove them and replace seals (I'm doing just that with my 96 Bronco).

The Throttle Position Sensor makes total sense as does the MAP and/or MAF sensors.

My hope is that the dealer will do whatever voodoo they have to, to find the problem. I know there should be pressure and function tests that they can run on the tranny to locate any problems and I believe they'll do that. I've already tried to pull the codes on my OBDII reader but none are there, so whatever happened did NOT set any trouble codes.

The dealer we go to has been pretty good about fixing stuff either on our now sold GMC or on this Tahoe.

In any event, the wifeoid is taking the truck to the dealer this AM and I'm confident that I'll hear something later this morning or this afternoon.

Will keep y'all posted.

 

[LJPinDrakeND]

UPDATED

Got a call from the dealer a little while ago. COULD NOT DUPLICATE THE PROBLEM!!

Up til now I thought maybe this dealer was a bit different.

I know from the questions that the service guru asked me that he didn't even read my "missive" that I typed out last night. Every single question he asked was covered in that statement/explanation/missive.

I'm guessing here but I'd almost be willing to bet that they took it for a drive, jinked it around, and couldn't duplicate the problem.

They're going to keep it over night and try again in the morning. Well that's not going to do a damn thing! When the problem occurred, the transmission was NOT cold. It had been running a while.

How do I get them to perform the tests that I know have to exist in whatever service manual written by GM that they use?

He even told me there were no codes. I KNOW THAT!! I looked myself.

I guess I'm going to have to wait for this tranny to burn itself up. Hopefully it will happen before 100K miles.

 

[TheFuzz]

Sounds like you would be better served by dropping the trans pan and checking for debris and/or metal shavings. That would at least give you a better sense of whats going on with it, and either help you plot a more direct course of action, or give you a little peace of mind.