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Backstory: took my vehicle (2017 Tahoe) in for basic scheduled maintenance - no issues. Had the transmission flushed at 97k because we were advised to do it before mileage hit 100k. Within a week after the flush, my truck sounded like a tractor. Took it back to dealership that did the flush. They stated the mechanic thought the seal would be ok when he did the flush but it is a high mileage vehicle and the seal leaked. We paid to replace the seal and they refilled all the fluids. The truck ran ok on the way home but soon started making noises that continued to get worse until the transmission wouldn't shift at all. Had it towed back to dealership. They now say the torque converter is bad and want to charge me $7200 to fix it. Could their initial mistake of not replacing the older seal they "thought" would "hold" and then all my fluids leaked out have caused this? $7k is a lot to fork out after they've had it twice already and possibly caused this. Please send your thoughts on if the two are related and if one could have caused the other.

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    Welcome to Motor Vehicle Maintenance & Repair! I'm guessing the transmission is a 6L80e (like is in my 2018 Silverado). If so, I'm wondering why it is having any issues at all? 97k is NOT a lot of miles. The 4L60e in my 2006 Silverado went 193k miles with zero issues, and the 4L60e was a BY FAR weaker tranny than the 6L80e. I have no clue where they get the idea 97k is "high mileage"? Unless they are abused, these trucks should be able to go 250-300k miles with regular maintenance. Just changing out the transmission fluid should not have caused you issues, unless they did something wrong. JMHO Oct 28, 2021 at 16:48
  • Thanks for the welcome and words of wisdom! I have no idea what transmission is in it, I'll look. It's been to this dealership for regular maintenance since we bought it from them. This flush was recommended as regular maintenance and we had no issues before. It's very frustrating bc now what seems like something that is their fault, they want to blame on "deeper issues" and keep tossing around high mileage. Truck definitely hasn't been abused. Used for school, work, extra curricular activities. I truly appreciate all the input so I can confer w/ dealership w/ some sort of knowledge.
    – HKH
    Oct 28, 2021 at 17:10
  • It sounds from your description the truck is going to need some work done on the transmission. I'm pretty sure the flush is what caused your issues, but you have NO WAY to prove this was the case. If I were you, I'd take the truck to a different shop ... some place which deals with transmission issues. Not only will they most likely give you the straight skinny, they'll also charge you a whole butt ton less to get it fixed, whatever the issues are. It sounds to me like the dealership is just trying to throw parts at it. All that's going to do is cost you more and more $$$. Oct 28, 2021 at 21:07

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Low fluid ( half empty) in the torque converter might cause problems for the many thin steel turbine blades, but I think it is unlikely. ( Long ago, working on automatic transmissions , it was not unusual to find bent turbine blades in the torque converters, a loss of efficiency but they performed relatively normally). Much more likely is low fluid cause low pressure on the servos that apply clutches and bands; low pressure permits them to slip. Abnormal slippage like this can burn/destroy the friction linings in a few minutes. A relatively moot point; improper service caused failure of the transmission regardless of the failure mechanism.

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  • Good info!! thank you for the feedback!!
    – HKH
    Oct 28, 2021 at 17:11

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