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My transmission got hot yesterday on my 04 Tahoe.It has a pretty mild 6.0 and the transmission is a stock junkyard trans out of a Vortec max truck that also had a 6.0. It should have about 140,000 miles on it. Yesterday it started shifting from fourth to third on the highway and then I got a "Transmission Hot" message. I changed the fluid today which was a pain in the *** since the Speed Inc. Y was seized onto the headers! The fluid was a little dark but there was not an alarming amount of debris in the fluid. I installed a new filter as well as a corvette and Sonnax Superhold servo. I ordered a cooler but it won't be here for a week. Enough history.
I was afraid that the band was slipping in fourth causing it to feel like it was in third since the 3-4 clutches would be engaged. But it doesn't slip at all in 2nd. That's what went first the last time I lost a band. Then I was looking through the tune and saw that it commands a 4-3 downshift at highway speed when its hot. So I'm hopeful that that's what was happening. Now I just need to figure out why it got hot. I suspect that the Torque converter is slipping and causing it to heat up. I have set it to not lock and I'll monitor my temperature on my 30 mile drive to work tomorrow. I can say this, it shifted great when I took it around the block after the servo install and fluid/filter change.
I welcome any advice but I'm really just documenting my situation.
Yes, the stock tunes reduce the use of 4th gear when hot. So hopefully 4th gear and the band are OK.
Since it sounds like you can monitor the trans temp (with HP Tuners?) I'm confident you will be able to figure this out. I'm sure the external cooler will help.
I do use HPTuners. I set the torque converter to stay unlocked and monitored it on my drive to work and back. It gets up to a little over 220 degF by the time I get to work. I ordered a cooler but its going to take a while to get here. I'm thinking about setting the converter to lock again and see if it gets hotter or not. If it does, I assume the clutch is slipping and making heat but I have a feeling it won't make much difference. I'd expect it to keep it from getting hotter on the highway. I don't want it running that hot but I have to drive it.
On a positive note, the new corvette and sonnax superhold servos have it shifting quickly and crisply!
Ok, now I'm asking for ideas. My transmission doesn't seem to be slipping or acting up at all but the temperature just keeps climbing whether I'm driving down the highway or idling. I topped off the radiator today and commanded both fans on to get the ect down but the stock radiator cooler is all there is. What could be causing it to get this hot?
Could it be from the header being so close to the pan? There's a gap but only about 1/4". Maybe less.
Just a guess:
When idling the stock cooler will actually increase the trans fluid temp to the same temp as the radiator fluid which might be in the 220F range.
Just a guess:
When idling the stock cooler will actually increase the trans fluid temp to the same temp as the radiator fluid which might be in the 220F range.
I added to my previous post. It was at 255 and climbing when I got home.
This morning on the way to work it never got above 200*. I was moving most of the time and I have the converter set to lock. The transmission shifted perfectly. I no longer suspect a mechanical problem with the transmission. The heat must be coming in from the exhaust. These shitty headers and Y are very close to the pan and I wouldn't even be surprised if it was touching yesterday. I pulled it down as much as they'd give to make the gap as big as possible and it seemed to help this morning. I'll be putting some header wrap on the y pipe under the trans pan at lunch today.
That's my fault. I went back and edited that post after you had already responded. I got some header wrap on that pipe. We'll see if that helps on my way home this afternoon.
Maybe try a heat heat shield instead of Header wrap? I've seen some of our diesel guys use it instead of the wrap for there turbo pipes and it was much better than just the wrap. maybe do both?
-Dalton
__________________ FTI COMPETITION CONVERTERS AND TRANSMISSIONS "IT'S NOT CHEATING, IT'S THE COMPETITIVE EDGE." 1-866-726-8358 info@ftiperformance.com FTIPerformance.com FTI Converter build sheet
Maybe try a heat heat shield instead of Header wrap? I've seen some of our diesel guys use it instead of the wrap for there turbo pipes and it was much better than just the wrap. maybe do both?
-Dalton
Thanks for jumping in! Could my converter be causing this? I've been noticing some shudder on lockup and sometimes it unlocks when I'm sure it's supposed to be locked. I was on the highway when that happened so I couldn't check my data log to see if it was commanded to lock. Instead I commanded it to stay unlocked in case it was the problem. Anyway, I'm suspecting the converter. I know that there are thousands of people running the same y pipe without issue. This is taking all of the fun out of driving. I'm just pissed at everyone in front of me keeping me from getting where I'm going while my temperature climbs.
Here's the story. I swapped the 4.8 for a 6.0. The stock transmission immediately started slipping in 2nd. I bought a good 4l60e from a vortec max truck (6.0) and put it in with a rebuilt trailblazer stall but I ruined that converter during the install by using a long bolt by accident and driving it into the back of the converter. So instead of buying another converter I just put the one from that 4.8 transmission in. I don't know what it is but it stalls to about 2000 rpm.
Ah, I remember your "long bolt" fiasco now from another thread.
Perhaps FTI will make you an offer you can't refuse.
We'd definitely be willing to check out your converter for you to see what we can find. Depending on what we find we could get you going with a new converter that will be much more reliable!
Ted does the 4L60/65 command lock-up in fourth gear? Maybe this was the slippage he was feeling when he originally got the trans hot?
-Dalton
__________________ FTI COMPETITION CONVERTERS AND TRANSMISSIONS "IT'S NOT CHEATING, IT'S THE COMPETITIVE EDGE." 1-866-726-8358 info@ftiperformance.com FTIPerformance.com FTI Converter build sheet
Last edited by FTICONVERTERS; Oct 20, 2016 at 11:32 AM.
Yeah. I've had an unusually hard time with transmissions on this truck. I'm trying yto everything quick and cheap and it bites me in the ***. My 8 month pregnant wife is getting tired of me having to spend weekends on it when I need to be working on the baby room. I'm grabbing a re manufactured trailblazer converter since I can buy one locally and I'll get it swapped in on Saturday. Man I hope that is the problem or I have some explaining to do. Also, I'm still waiting on that damn cooler. I bought it on amazon but its not one of the prime items so there's been no hurry to get it to me.
FTI I just saw your post. Thank you for the offer. I drive this truck every day to work and I have to have it so I have to go with something I can find locally so I can get it done now. I have HPTuners so I have driven it with lockup disabled and enabled with the same results. I have PWM disabled in the tune either way. If it's making excess heat, it's doing it even at idle. Is that possible?
FTI I just saw your post. Thank you for the offer. I drive this truck every day to work and I have to have it so I have to go with something I can find locally so I can get it done now. I have HPTuners so I have driven it with lockup disabled and enabled with the same results. I have PWM disabled in the tune either way. If it's making excess heat, it's doing it even at idle. Is that possible?
Not a problem! I have a sneaking suspicion that the converter may not be your issue. If you still go with the new converter, let us know how it does.
Originally Posted by mrvedit
The trans and converter should not be generating much heat in idle and in Neutral/Park.
And only a little in idle and Drive.
As Axekick posted, he has HP Tuners and has tried both locking and unlocking the converter without much difference.
That makes me think the converter may not be the issue... there should be a noticeable difference between the 2 if the converter was slipping in lock-up.
__________________ FTI COMPETITION CONVERTERS AND TRANSMISSIONS "IT'S NOT CHEATING, IT'S THE COMPETITIVE EDGE." 1-866-726-8358 info@ftiperformance.com FTIPerformance.com FTI Converter build sheet
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Overheated Transmission - 4l60e 
