GM 2020 Silverado HD 6.6 Gas - Bad Transmission

DIY motorhome anyone ?

www.allisontransmission.com

Allison Transmission Announces Collaboration with Freightliner Custom Chassis Corporation on Walk-In Van Program

Uprate variants of Allison’s 1000 Series™ and 2000 Series™ transmissions designed to integrate with the new GM 6.6L gasoline engine.
www.allisontransmission.com www.allisontransmission.com

6.6L.JPG
 
Dru2u said:
I'm going to have to look at my manual again for this truck. I want to say that it says the fluid level can be check, but that service is not necessary. Which to me means, the fluid is good until the part it is servicing fails, which is a bunch of crap.

If it says nothing about servicing, I'm going print the page you've attached and insert it in my manual as if it was an addendum from the manufacturer. :LOL:
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The fluid level can be checked and the unit is fully servicable, its just a PITA to do. Any 6L90 in a GM HD from 2021 thru 2023 has provisions for a trans dipstick. The parts are less than $50 from GM. Its a pretty straightforward mod.
The 6L90 has some issues with the Torque converter being weak. If it fails the debris wipes out the pump and then the rest of the trans. If I had kept my 2021 3500HD gasser my plan was to replace the TC after the 36k warranty. I ended up selling it and buying a 2024, not for the 10 spd but because I got stupid money out of my 2021.
 
64bawagon said:
The fluid level can be checked and the unit is fully servicable, its just a PITA to do. Any 6L90 in a GM HD from 2021 thru 2023 has provisions for a trans dipstick. The parts are less than $50 from GM. Its a pretty straightforward mod.
The 6L90 has some issues with the Torque converter being weak. If it fails the debris wipes out the pump and then the rest of the trans. If I had kept my 2021 3500HD gasser my plan was to replace the TC after the 36k warranty. I ended up selling it and buying a 2024, not for the 10 spd but because I got stupid money out of my 2021.
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It is ood they didn't put a dipstick in. My 2017 6L90E had one.
 
Its impossible to know exactly what their motivation is/was but I have to believe it was partly due to money and partly due to people not following the correct procedure for checking the level. This is an issue across many vehicles. I conducted quite a few training on the procedure on our vehicles at work and some guys still never really had a grasp on it (some just dont GAF)
I think GM did it more to give relief to the dealers having to address it than anything else. The fact that some folks have pushed this "sealed for life" BS is a good example.
The 10L1000, had it actually been designed by Allison would have had provisions for easy maintenance like the 1000 series before and every other of their 3000 and 4000 series. Allison knows how to build an easily serviced trans.
 
64bawagon said:
The 6L90 has some issues with the Torque converter being weak. If it fails the debris wipes out the pump and then the rest of the trans. If I had kept my 2021 3500HD gasser my plan was to replace the TC after the 36k warranty.
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@64bawagon, You were going to preemptively replace the torque converter? That seems a bit extreme. With another OEM or something else?
 
AZjeff said:
@64bawagon, You were going to preemptively replace the torque converter? That seems a bit extreme. With another OEM or something else?
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Yes. Since the truck is/was used primarily for towing the 5th wheel, I was going to replace it with a Billet unit of better quality than the OEM. The 6L90 was a decent trans in my estimation but the Torque Converters GM uses are a weak link. Theres plenty of data on the 6L80 units around the 100K mark being wiped out due to the TC. I figured it would be cheaper to be proactive than have to replaced it on the road. Once the TC goes it wipes out the pump and the rest of the trans.
 
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.
 
A buddy of mine has the GM variant and the 10r80. No maintenance, torque converter started shuttering and slipping at just over 100k. They offered to replace the TC but couldn’t guarantee the transmission itself wasn’t damaged. A full trans replacement was $10k. He sold the truck that week.

I’m a “change the fluid at 60k then every 30 after that,” kinda guy. Maybe one could stretch that 30 out a little bit. But I haven’t.
 
meep said:
A buddy of mine has the GM variant and the 10r80. No maintenance, torque converter started shuttering and slipping at just over 100k. They offered to replace the TC but couldn’t guarantee the transmission itself wasn’t damaged. A full trans replacement was $10k. He sold the truck that week.

I’m a “change the fluid at 60k then every 30 after that,” kinda guy. Maybe one could stretch that 30 out a little bit. But I haven’t.
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Precisely why I have rarely bought used over my lifetime. People who are happy with a vehicle and have no issues are less likely to sell.
 
meep said:
A buddy of mine has the GM variant and the 10r80. No maintenance, torque converter started shuttering and slipping at just over 100k. They offered to replace the TC but couldn’t guarantee the transmission itself wasn’t damaged. A full trans replacement was $10k. He sold the truck that week.

I’m a “change the fluid at 60k then every 30 after that,” kinda guy. Maybe one could stretch that 30 out a little bit. But I haven’t.
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Had a 21 3500 that we put 194k miles on towing a 40ft flatbed most times loaded with 10k lb of freight. We did 50k fluid changes and when we sold it she ran like new.
 
64bawagon said:
Precisely why I have rarely bought used over my lifetime. People who are happy with a vehicle and have no issues are less likely to sell.
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There is a lot of truth in that, but I think there are also more subtleties too. I'd never buy a used car/truck that is < 2 years old, as that is usually the point where lemons are given back or sold when guys are tired of dealing with constant problems etc.

2 to 4/5 years is where a lot off lease stuff gets returned. If I see an off lease I'll be interested if its not a rental.

But some guys trade off stuff because life changes, downsizing or upsizing are common too. Trouble is how do you know?

Carfax is a great tool, none of my service records show up there because I do it myself but in my case I keep the recipts and detailed notes so if I sell privately that can give the new guy confidence.

Dealers don't care, which I find odd. I had all my records for my previous Jeep and he didn't even look at them, just an offhand "oh that's nice" and then he checks out the condition (scratches etc) and gives you a price based on mileage and years and features.
 
I like it. The 6.6 is a hoss, and the Allison is perhaps the best auto out there.

64bawagon said:
I have to believe it was partly due to money and partly due to people not following the correct procedure for checking the level. This is an issue across many vehicles.
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It should not be. Before these idiots went to the dipstick-less BS, it was not an issue. There was nothing wrong with a dipstick, other than it costs them 5$, which they turn around and charge another 15$ not to have the stick. No reason for this to be an issue. We as consumers should not have to re learn how to check an AT fluid level, especially in trucks. I understand the disposable models, like the equinox or Traverse not having one, but the truck?
 
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%.
 
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64bawagon said:
Yes. Since the truck is/was used primarily for towing the 5th wheel, I was going to replace it with a Billet unit of better quality than the OEM. The 6L90 was a decent trans in my estimation but the Torque Converters GM uses are a weak link. Theres plenty of data on the 6L80 units around the 100K mark being wiped out due to the TC. I figured it would be cheaper to be proactive than have to replaced it on the road. Once the TC goes it wipes out the pump and the rest of the trans.
Click to expand...
YOU ARE CORRECT! Every 6 speed I have replaced had horrible pump whine and shudder...right around those miles too! I did not think about what you said until you said it.
 
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