GM 2020 Silverado HD 6.6 Gas - Bad Transmission

[Sedin26]

I understand not enjoying seeing good equipment ruined; but at the end of the day it is a work truck that belongs to your work, not you. How they choose to maintain it isn’t really your business unless you are in charge of maintenance. Not worth the stress you are experiencing.

Correct.

Run it until it dies and then they can fix it or replace. You can’t care about it more than they do and it’s not worth the energy to even consider it.

 

[clinebarger]

We do about 2-3 of these 6 speeds a month. The avg miles when they die 110k-140k. Most all I've seen never had service but a few did not until they noticed issues so it was too late. My personal opinion - they are not the best but not the worst trans made but I strongly suggest doing fluid changes before 100k miles normal use and much sooner if towing. I would think no matter what service it sees a 50k mile interval would do a lot to extend life.

With all that, let's see what @clinebarger recommends because he is THE man on transmissions (especially GM) - he is to be trusted 100%.

The 6L80/6L90 are at their core a very good transmissions with a subpar converter clutch & horrible converter clutch apply/release calibration.
And the Pressure Regulator Valve wear is pretty common causing pressure spikes that can crack the 1234 Piston &/or the 1234-35R Drum.

I use a Billet front cover Twin Disc converter on every 6L80/6L90 unit I build, Takes less regulated apply pressure to apply the clutch on this converter.
The calibration/strategy uses the least amount pressure to meet the desired TCC slip RPM. Some data logs I've taken has shown it takes 25-50% less per the TCC Regulator Solenoid duty cycle.
Meaning you have more head room as the TCC Regulator Valve/Bore wears.......Instead of a stock converter needing 60% duty cycle to hold a 20/40 slip rpm, This converter can hold a 0-5 slip rpm at @ 10-20% duty cycle.

Sonnax Zip Kit, Has a (main) Pressure Regulator Valve with longer lands to reduce wear from side loading, Also has a sleeved TCC Regulator Valve to restore hydraulic integrity to the TCC apply circuit which I'm sure contributes to the lower duty cycle to control slip error.

Tuning is an absolute must in my opinion, I reduce ALL desired TCC Slip tables to Zero RPM, And Disable TCC Apply in 1st through 4th gears.
If in a vehicle with AFM...I disable it as with Zero TCC Slip it can cause some strange vibrations/frequencies in V4 mode. Most AFM calibrations have 20 RPM desired for V8 mode & 40 RPM desired for V4 mode.

Heavy duty units (6L90E) use a 20 RPM desired across the board which helps with TCC longevity & don't normally apply the TCC in 1st gear, Some early calibrations don't apply the TCC until 3rd gear which is why some go a lot longer.

 

[clinebarger]

WOW! We do new remans with 3yr warranty for about 3k for the trans plus install and programming...little over 4k.

I'm at $4,800 with a Billet Converter, Sonnax Zip Kit, Sonnax 1234 piston, Borg Warner Frictions, OE Molded Pistons, Durabond Bushings, OE 456 & 35R Steels, Tuning, Along with a OE Bellhousing, Stator, & Rotor Kit.
Installed & Flush the Cooler/s with a 3 year 100,000 warranty.

The TECHM is where the struggle lies, I can usually salvage the original with a thorough cleaning & replacing the pressure switch membranes.
I've had great luck using 6L45E/6L50E TECHM's from Global A platforms (ATS/Camaro) & I can buy a whole unit for under 1/2 what a reman TECHM from GM costs. Long as it has a compatible P/N ....I can stand alone flash it with SPS2.

Sonnax has a a pretty comprehensive cross reference for what TECHM's are compatible with each other.....As an example all these P/N's are compatible with each other.
OE Part No. 24256939, 24257213, 24259639, 24259835, 24261870, 24264141, 24265259, 24267576, 24270598, 24275873, 24276637.

 

[Exhaustgases]

I'm at $4,800 with a Billet Converter, Sonnax Zip Kit, Sonnax 1234 piston, Borg Warner Frictions, OE Molded Pistons, Durabond Bushings, OE 456 & 35R Steels, Tuning, Along with a OE Bellhousing, Stator, & Rotor Kit.
Installed & Flush the Cooler/s with a 3 year 100,000 warranty.

The TECHM is where the struggle lies, I can usually salvage the original with a thorough cleaning & replacing the pressure switch membranes.
I've had great luck using 6L45E/6L50E TECHM's from Global A platforms (ATS/Camaro) & I can buy a whole unit for under 1/2 what a reman TECHM from GM costs. Long as it has a compatible P/N ....I can stand alone flash it with SPS2.

Sonnax has a a pretty comprehensive cross reference for what TECHM's are compatible with each other.....As an example all these P/N's are compatible with each other.
OE Part No. 24256939, 24257213, 24259639, 24259835, 24261870, 24264141, 24265259, 24267576, 24270598, 24275873, 24276637.

Questions,
1 You say Billet Converter, then it would be a bolt together unit? Doing billet and welding seems not worth it.

2 Its been awhile for me doing a GM unit, the last trans I did was a Jatco CVT, flow control valve worn bad (its a regulator, and the result is lower pressure and belt slippage etc) , it seems the manufactures fascination with aluminum valves and valve bodys doesn't work too great, yes the valves are coated but it wears off just like other coatings do. Back in the very old days of no aluminum used in a valve body I don't remember seeing so much wear.
Just asking your opinion.

3 You mentioned regulator valve wear, and piston cracking so when they wear it' not a loss of pressure deal then? If so seems counter intuitive, and or my lack of dealing with those transmissions.

 

[dja4260]

I'm actively looking to purchase a 2018-2019 Chevy 2500 with the 6.0 and 6L90 to tow a small 5th wheel (~7600 lbs dry). Assuming maintenance is kept up, is there a more reliable engine/trans combo out there in the 2018-2022 age range?

I know in my price range is a Ram w/ 6.4, F-250 w/ 6.2, chevy w/6.6 (top of budget)...

 

[burbguy82]

2018-2019 Chevy 2500 with the 6.0 and 6L90

I would go a little older, it will be cheaper.

IMO, the 6.0 Vortec is the best all around truck engine ever made. So yes, do it.

 

[64bawagon]

I would go a little older, it will be cheaper.

IMO, the 6.0 Vortec is the best all around truck engine ever made. So yes, do it.

We had several 6.0 trucks at work. Having driven and worked on them I can say the 6.6 is hands down a better engine in terms of power and economy. As far as longevity goes the 6.0 has a proven track record and will take some neglect. The 6.6 hopefully will be as good.

 

[hemioiler]

I'm actively looking to purchase a 2018-2019 Chevy 2500 with the 6.0 and 6L90 to tow a small 5th wheel (~7600 lbs dry). Assuming maintenance is kept up, is there a more reliable engine/trans combo out there in the 2018-2022 age range?

I know in my price range is a Ram w/ 6.4, F-250 w/ 6.2, chevy w/6.6 (top of budget)...

If you're going Ram, I'd suggest 2019+ (which is the new 4.5 gen truck) as they have the ZF 8 speed transmission instead of the chrysler 6 speed found in the 4th gen 2500s. 2 more gears, but far better tuning, reports of guys pulling with the 6 speed say they can run into tranny temp issues and poor upshift/downshift strategys around 2n'd gear.

If you're going GM, the 6.6 appears to be a great engine with DI being the only negative for some. I know its the upper end of your budget but again I'd consider the 10 speed "allison" in the 2023's instead of the the 6 speed in previous model years, with towing the extra gears is always a benefit.

Don't know much about the Ford, pretty sure it has its fans as well.

When it comes to price, the Ram will most likely be cheapest all else being equal, however cabin space is also the smallest and generally it has a little less payload vs the other 3/4 tons in case either of that matters to you.

 

[burbguy82]

We had several 6.0 trucks at work. Having driven and worked on them I can say the 6.6 is hands down a better engine in terms of power and economy. As far as longevity goes the 6.0 has a proven track record and will take some neglect. The 6.6 hopefully will be as good.

I agree, the 6.6 has more power and economy. The 6.0 is a known, nearly bulletproof engine. The 6.6 might prove to be as good, but I could see a high level of maintenance required.

If the 6.0 Vortec, L96 for example had a displacement of 6.6, and the intake to feed it, the argument on power would be moot. But I am no expert.

 

[GMBoy]

I'm at $4,800 with a Billet Converter, Sonnax Zip Kit, Sonnax 1234 piston, Borg Warner Frictions, OE Molded Pistons, Durabond Bushings, OE 456 & 35R Steels, Tuning, Along with a OE Bellhousing, Stator, & Rotor Kit.
Installed & Flush the Cooler/s with a 3 year 100,000 warranty.

The TECHM is where the struggle lies, I can usually salvage the original with a thorough cleaning & replacing the pressure switch membranes.
I've had great luck using 6L45E/6L50E TECHM's from Global A platforms (ATS/Camaro) & I can buy a whole unit for under 1/2 what a reman TECHM from GM costs. Long as it has a compatible P/N ....I can stand alone flash it with SPS2.

Sonnax has a a pretty comprehensive cross reference for what TECHM's are compatible with each other.....As an example all these P/N's are compatible with each other.
OE Part No. 24256939, 24257213, 24259639, 24259835, 24261870, 24264141, 24265259, 24267576, 24270598, 24275873, 24276637.

One thing I did not mention in my post was the transmissions I get have been troublesome as LKQ bought up most all the reman companies. I did a 2019 Tahoe last month and the 1st trans - bad had terrible pump whine, the 2nd the TCM was bad and took down the whole truck after about 20 miles and also had minor pump whine...the 3rd one worked fine. LKQ has approved my labor claims for both claims and I don't know how they make money with the junk the sell and I am referring to NEW/REMAN not their used which has been fine but wont't do used because the of risk involved with these trans to start and that I cannot reprogram the Gobal A module with SPS. GM won't allow it so new TCM is the only way I can do it.

Next GM trans job I am bringing to you for rebuild as your warranty is the same as a reman but with BETTER quality and parts. I am not that far up 287 from you.

Side bar - I have 2 vehicles here in the que for transmissions - 2015 Impala 3.6 6L80 and a Nissan Armada. Do you do Nissan trans?

 

[64bawagon]

I agree, the 6.6 has more power and economy. The 6.0 is a known, nearly bulletproof engine. The 6.6 might prove to be as good, but I could see a high level of maintenance required.

If the 6.0 Vortec, L96 for example had a displacement of 6.6, and the intake to feed it, the argument on power would be moot. But I am no expert.

I really think the 6.6 was modeled after the 6.0 with a few tweaks. why mess with success. One of the best parts is no AFM or whatever they call it.
I have about 7k on mine and I was going to grab a sample when I changed the oil last time but I messed up and left the bottle on the workbench. At my age I figured the likelyhood that I could shimmy out from under the truck and get the bottle soon enough to get a good sample was thin so I will wait to next time and hope I remember it then.

 

[burbguy82]

At my age I figured the likelyhood that I could shimmy out from under the truck

I feel you on that one.

 

[clinebarger]

Questions,
1 You say Billet Converter, then it would be a bolt together unit? Doing billet and welding seems not worth it.

2 Its been awhile for me doing a GM unit, the last trans I did was a Jatco CVT, flow control valve worn bad (its a regulator, and the result is lower pressure and belt slippage etc) , it seems the manufactures fascination with aluminum valves and valve bodys doesn't work too great, yes the valves are coated but it wears off just like other coatings do. Back in the very old days of no aluminum used in a valve body I don't remember seeing so much wear.
Just asking your opinion.

3 You mentioned regulator valve wear, and piston cracking so when they wear it' not a loss of pressure deal then? If so seems counter intuitive, and or my lack of dealing with those transmissions.

My guy uses a stock JMBX converter & welds on a Billet Front Cover using a Twin Disc kit from Sonnax. Here's a video "Sonnax"

"6Lxx" units like to wear the land that separates the Balance Oil from Converter Charge/Cooler feed, Balance oil leaks into the converter charge & the Regulator Valve can no longer balance correctly.
There are basically Increase & Decrease Spools on the Regulator Valve, 6L's like to wear the Decrease end of the valve. Other regulation valve styles wear the Increase end causing low line pressure.

Also of note is these units use a Variable Displacement Vane Style Pump that can really put out some pressure when unchecked.

 

[clinebarger]

One thing I did not mention in my post was the transmissions I get have been troublesome as LKQ bought up most all the reman companies. I did a 2019 Tahoe last month and the 1st trans - bad had terrible pump whine, the 2nd the TCM was bad and took down the whole truck after about 20 miles and also had minor pump whine...the 3rd one worked fine. LKQ has approved my labor claims for both claims and I don't know how they make money with the junk the sell and I am referring to NEW/REMAN not their used which has been fine but wont't do used because the of risk involved with these trans to start and that I cannot reprogram the Gobal A module with SPS. GM won't allow it so new TCM is the only way I can do it.

Next GM trans job I am bringing to you for rebuild as your warranty is the same as a reman but with BETTER quality and parts. I am not that far up 287 from you.

Side bar - I have 2 vehicles here in the que for transmissions - 2015 Impala 3.6 6L80 and a Nissan Armada. Do you do Nissan trans?

I program them standalone with a bench harness using the manual VIN entry in SPS2. There is no VIN in T43 6Lxx controllers....But it has to be the correct Operating System to be compatible. You can change the OS with SPS2 IF the TECHM part number is compatible with the original.