2019 Tahoe Transmission Won't Shift

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TonyBrsd

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I have a 2019 Tahoe LT with 126500 miles, and about three or four months ago, I had some rough shifting, so I brought it to a mechanic friend of mine, and he changed the fluid(not flush). When he dropped the pan he did notice a lot of particles in the pan, magnet, and filter. When he changed the fluid and filter, that seemed to have fixed the problem. Shifting was smooth, but I experienced minor shuttering when accelerating, usually at higher speeds. Transmission temp was always normal around 190.

Yesterday, I was driving from Houston back home to Louisiana, and I was almost home, and all of a sudden while doing 45 mph, my rpm's went up like it shifted into neutral, and I couldn't get it to move. I was stuck in traffic, but after a little time, I was able to get it to move and drive enough to move it out of traffic onto the side where a tow truck could get me. I recently had a loose battery terminal a few weeks ago (the new battery had a slightly smaller post than the factory terminal connection), and one of the errors on the screen in the middle of all of this yesterday was a critically low battery, so I bet the terminal was loose again. I had just traveled over some rough stretch of road right before this, and maybe it had come loose. I have read that sometimes that could be the case when there's not enough power to control the transmission it won't shift. Even the woman at O'Reilly Auto Parts, when I bought the new terminal cable, said that her husband experienced the same thing where a battery cable was loose, and the transmission wouldn't shift, and once they fixed it, that solved the problem.

This morning I changed the battery terminal to get one that clinched tighter. I started the vehicle and was able to move forward and reverse and then forward again, but when I went to reverse again, it was the same thing with no movement, like I was in neutral. My mechanic thinks we could change the fluid out again to try to get whatever particles were left in there since the magnet was now clean and should catch some of the remaining particles. I'm just reaching out here to see for advice before I have to buy a rebuilt transmission.

Just looking for advice before having to shell out some serious dough.
 

NickTransmissions

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Yep, time for an overhaul...I'm assuming you have a 6L80 but if not, situation is the same...False-neutral conditions as described, when combined with shuddering is almost always torque converter...The debris you/your mechanic saw came from the converter. Unfortunately, when damage like this is sustained in the TC, the entire transmission has to be overhauled due to metal/particulate contamination. Additionally, the pump will either need to be completely resurfaced and rebuilt or replaced.

If you have a 6L80, check out my 6L80 Info Thread (link is in my signature line) for a complete list of parts and procedures that I perform on all these units when I go through them...You can compare that list to the information shops provide to you if/when you start calling around.

The IMS, TEHCM and speed sensor harness/assembly should also be replaced as tiny particulate metal debris has likely made its way into the TEHCM as well as valve body and pump valve trains so you may or may not need a valve body as well.
 
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TonyBrsd

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Yep, time for an overhaul...I'm assuming you have a 6L80 but if not, situation is the same...False-neutral conditions as described, when combined with shuddering is almost always torque converter...The debris you/your mechanic saw came from the converter. Unfortunately, when damage like this is sustained in the TC, the entire transmission has to be overhauled due to metal/particulate contamination. Additionally, the pump will either need to be completely resurfaced and rebuilt or replaced.

If you have a 6L80, check out my 6L80 Info Thread (link is in my signature line) for a complete list of parts and procedures that I perform on all these units when I go through them...You can compare that list to the information shops provide to you if/when you start calling around.

The IMS, TEHCM and speed sensor harness/assembly should also be replaced as tiny particulate metal debris has likely made its way into the TEHCM as well as valve body and pump valve trains so you may or may not need a valve body as well.

Thanks for the reply. My mechanic checked on a rebuilt tranny and that's around $2,700 his cost, plus his labor. It sucks but I guess it's the only thing to do now.
 

NickTransmissions

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I think he called Oreily. It should have a warranty on it. He explained that rebuilding or a remaned is about the same in cost
Yea, hard no on those auto parts store units for me (taken quite a few apart across a variety of transmission types over the years and they leave a lot to be desired) but you can ask him if it comes with all of the below:

Parts List for Overhaul
PARTGM Part #Notes
Paper and rubber kit
Clutch moduleBW factory OEM or high energy (upgrade option for DDs: Raybestos Stage One or Alto HE/Carbon-Kevlar)
Kolene steel module for 3-5-R and 4-5-6 clutch packs
Factory steel module for 1-2-3-4, 2-6 and low reverse clutch packs
Bonded steel and rubber balance piston kitOEM pistons are made by National Seal
Snap ring kit for the 3-5-R and 4-5-6 clutch pack return spring assemblies24260139Early spring kit listed will service all years
Snap ring for the rear sprag assembly-to-center support24230752Will retro to 2006-E2007 units
Snap ring for the 4-5-6 hub damper cover plate
38 element sprag clutch assembly24248957Will retro to 2006-E2007 units
GM heavy duty parking rod assembly (2017 and older)2428004812.5" for 6L80E and 14.5" for 6L90E
Factory bushing kit
Thrust bearing kit (only needed if trans overheated)
Sonnax billet aluminum 1-2-3-4 apply piston
Sonnax 4-5-6 piston kitOptional but strongly recommended - adds one additional friction and flat steel to the clutch pack
Sonnax Zip KitTransgo Reprogramming kit (TowNPro) is a viable alternative
Sonnax Oversized Clutch Boost Valve kitNecessary if one or more existing clutch boost valves fail vacuum test or prove to be worn; requires Sonnax reamer and related tooling for installation
GM internal mode switch24246427Updated switch will retro to years 2006-E2007
GM wiring harness and speed sensor assembly2012+: Application dependent and must match existing rear speed sensor design - consult dealer w/VIN
GM separator plateYear/application specific - consult dealer w/VIN
GM TEHCMOptional for later model units and strongly recommended for pre 2014 units; year/application-specific - consult dealer w/VIN
Sonnax pressure switch rebuild kit and toolPurchase if intending to re-use TEHCM
GM TEHCM filter screenPurchase if intending to re-use TEHCM
New Torque ConverterNew converter should come w/ converter clutch thickness => .050"; billet cover strongly recommended for heavy duty or high performance
Machine Work
PumpMachine pump cover and body. Cut pocket to achieve .001-.0015 clearance between rotor/slide and deck surface
3-5-R DrumReinforce welds at the base of the drum (all years)
Weld-reinforce hubsWeld-reinforce 1-2-3-4 and 4-5-6 clutch hub w/tig welder for HP/HD units

See if @BlackBearPerf has a good tune to pair with the new transmission as these clutch to clutch units def benefit from some performance command/control tuning...
 

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