6 Speed vs 8 Speed Reliability

[SilveradoCustom]

Hi all,

 

I'm considering a Silverado Custom, 5.3L 4x4. I don't need anything fancy, just something to pull my 4500 lb boat during the summer without any issues.

 

I'm trying to figure out how reliable the 6 speed auto is in the Custom trim with the 5.3L. It looks like it craps out between 120-150k regardless of maintenance and use. 

 

I really would rather stay away from the 8 speed at all costs, which is why i am looking at the 6 speed.

 

What's your thoughts on this transmission? Good, or should I be worried, especially since I'll be buying used?

Thanks for any input.

[1SLOW1500]

6speed good 8speed not so much. That is all

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[HeySkippyDog]

[emoji2369] The 6L80 is by no means a new model transmission. It's been around.

I would expect more longevity from a 6 than an 8.

You can increase its lifespan considerably by doing the following:
-fluid change every 60-80k
-staying with stock tire sizes for wheel size
-keeping the differential healthy
-maintaining proper tire pressure

You have to take the "my transmission blew at 40k miles" posts with a grain of salt. Most times, there was an aggravating factor that broke it on the 6 speed. Not just a bad design.

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[SilveradoCustom]

It seems a lot of the 6 speed failures were on trucks that were modded (lifted/big tires) or poorly maintained (never had oil or fluid changes, overheated, etc.) At least from what I can tell researching the past couple of days.

 

The 8 speed failures are on new trucks - stock, and with mileage often too low to even make it to their first transmission service. 

 

I keep my vehicles until they rust out to the point of being unsafe. I'm not afraid to wrench, but I don't want to wrench any more than necessary.

 

A 6L80E is what, 2k? I figure if I need to do a trans swap at 150k, I'll probably have gotten my money's worth out of the truck by then. 

[dieselfan1]

6 spd been around for years nothing wrong with it at all.

Just because some have failed ( more than likely due to abuse or lack of fluid changes) that don't mean they are all going to fail between 120,000 and 150,000 miles. Don't believe what you " heard on the internet" . It's BS. 

[Doublebase]

Good to hear some good things about the 6 speed, because I own one and hate the thing. At 41,000 miles I was worried enough to drop the pan, change the filter, fluid and clean the magnet...with the way this things shifts, shutters and shakes, I was expecting metal shavings on that magnet, but it looked good. Suppose/hope that means the transmission is ok, even if it doesn't behave the way I'd expect. 

 

My thought process is...let me get 150,000 miles out of this thing and then I won't feel bad about replacing it and spending a couple grand. I figure I can live with spending 2k if a I can reach 150,000 without problems. 

 

[HeySkippyDog]

Good to hear some good things about the 6 speed, because I own one and hate the thing. At 41,000 miles I was worried enough to drop the pan, change the filter, fluid and clean the magnet...with the way this things shifts, shutters and shakes, I was expecting metal shavings on that magnet, but it looked good. Suppose/hope that means the transmission is ok, even if it doesn't behave the way I'd expect. 
 
My thought process is...let me get 150,000 miles out of this thing and then I won't feel bad about replacing it and spending a couple grand. I figure I can live with spending 2k if a I can reach 150,000 without problems. 

 

Have you disabled V4 with a tune or Range V8 plug?

Both of mine were weird until I went full time V8, but not overly weird.

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[1SLOW1500]

All the complaints and issues in the 6speed are tune,adaptive tables, or defective parts(yes there was some).
There is world of slip in the stock tune.
I would look at temp for tran fluid and base the trans fluid change, filter, magnet on that.
I made it to 10k on my 6speed. But I watched it go and adjusted tune to see how much it can handle. I spent just under $8500 on trans and supporting mods. And spoke to many pros and all say same. Trans are good,convert weak but manageable, tune horrible, temp worst. Temp from wear or slip is what limits the trans. Power level and straight abuse aside. Stay under 200* but 180 is best.
The 8speed have been bad many updates and replacement parts and even new fluid type.

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[truckguy82]

I personally had a thermostat stuck closed in my 6l80. So every time I took it out I’d see temps around 210-230.

 

I can’t imagine how many trucks have this same issue but they have no idea. You have to actually select “trans temp” in the DIC to see it, and then you have to be aware of what’s normal. 
I can’t imagine more than 10% of truck owners actually monitor and know what’s not ok. The dealer having no idea how to diagnose or repair my issue means clearly nobody brings their truck in for it.
 

There were zero symptoms something was wrong.

[1SLOW1500]

I personally had a thermostat stuck closed in my 6l80. So every time I took it out I’d see temps around 210-230.
 
I can’t imagine how many trucks have this same issue but they have no idea. You have to actually select “trans temp” in the DIC to see it, and then you have to be aware of what’s normal. 
I can’t imagine more than 10% of truck owners actually monitor and know what’s not ok. The dealer having no idea how to diagnose or repair my issue means clearly nobody brings their truck in for it.
 
There were zero symptoms something was wrong.

In that case the truck should have dropped into a "hot" mode. Most people may not notice it but the software switches to shift lower in a attempt to reduce power and slip. Most call this a limp mode but that is different.
I have had many people argue the newest D6 is made for that. To them please read up on it. Simply stating it can is not the same as it should. There are charts that show the wear and fluid breakdown for all temperature levels. Then compare to how many miles before people change fluid and see where the issues is for most people. This is why I say 30kish drop pan and really clean it out. Then after that fluid only but still every 30k.

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[Doublebase]

15 hours ago, HeySkippyDog said:

Have you disabled V4 with a tune or Range V8 plug?

Both of mine were weird until I went full time V8, but not overly weird.

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Honestly I haven't and I probably won't for a while...I have a pretty big commute and gas mileage is somewhat important to me right now. And I'm averaging 24.5 mpg over the life of the vehicle (41,000 miles). That will probably change soon, as I am selling my house and moving a bit closer to work. 

[Hashtagthis]

The 8 speed is a solid tranny. Just some glitches. Check trans fluid often. If it gets over 180 or  If you haul anything or have bigger tires then perform the trans thermostat delete. Mine never goes over 140 degrees now. 

 

 

2017 Silverado 6.2. 8speed. Custom King Coilovers 2.5 in and Custom rear bypass Kings. 

Superstrength U joints. Custom tune. Custom CAI. BORLA ATTAK Cat back. 92 mm TBI. 490 HP. Faster. 

50k miles

6 inch lift

[truckguy82]

On 11/18/2019 at 1:22 PM, Doublebase said:

Honestly I haven't and I probably won't for a while...I have a pretty big commute and gas mileage is somewhat important to me right now. And I'm averaging 24.5 mpg over the life of the vehicle (41,000 miles). That will probably change soon, as I am selling my house and moving a bit closer to work. 

Get a tune, should increase mpg a bit and get rid of your trans issues.

[NomadicCPO]

8-Speed transmission has been the achilles of an otherwise great truck for me at 50k miles.

Started with hard 2-1 downshifts, which reprogramming fixed.  Then it was the torque converter shudder, which took them forever to figure out was being caused by water-loving fluid, but in the meantime was having flushes done every 10k miles as a bandaid.  Lately the 1-2 up shift has been randomly hard, and the deceleration downshifts have become more noticeable and a little clunky.

Will be pleasantly surprised if it makes it to 100k without needing a rebuild or replacement.

[Doublebase]

21 hours ago, truckguy82 said:

Get a tune, should increase mpg a bit and get rid of your trans issues.

A tune? Will I be able to keep my AFM if I get a tune? I'm already averaging 24.5, a tune would help me get better than that? I'm interested. Is this something that would void my power train warranty? If so I'll probably wait till I'm out of warranty.

 

Regarding the pan drop/filter/fluid change...it honestly has seemed to help...I haven't had the shutter going up the hill on the highway that it started doing it on. But I'm not holding my breath, I've never really seen a tranny fluid change do much of anything in regards to driveability, so if the shutter returns I won't be surprised.