GM 6L80 Transmission Information Thread

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ilikemikes

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Money says you are running a 3.42 gear ratio. What size tires are you running? I'm thinking smaller tires or a larger ratio, like 3.73.
I am looking into gears now...
Ran my VIN on this and its says 3.08 min to 3.42 max. Mech and powertrain specs say 3.08.
 

S33k3r

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3.73 gears might be the way to go then. And/or have your transmission tuned. Are you using tow/haul mode?
 

ilikemikes

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3.73 gears might be the way to go then. And/or have your transmission tuned. Are you using tow/haul mode?
As I mentioned before, I think I'm going to have to rebuild my transmission. Pretty good bump switching into Drive. Smoother after it warms up. Had to buy tires recently and went 1 size down to 32" from 33". Yeah I just started using tow/haul mode on hills when towing the boat. The trans shop does differential/transfer case work as well so might get some gears. As a part of the trans rebuild they will tune to tire size and towing so might hold off the gears. I was thinking gears because of another post of someone adding mods to get 500 hp and that sounds fun!!
 

S33k3r

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Higher (numerically) gears will multiple the torque you are producing so you get more work out of it. However, at highway speeds, this works against you by reducing your gas mileage; the engine has to rev higher at those speeds.

In a nasally, head up my a** kind of way: 500hp doesn't really matter. It is your foot-pounds of torque that move you down the road.
 

Pacfanweb

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Hey Nick,
16 Tahoe 6L80. Was rebuilt by a GM tech 2 years ago. Had an issue not going back to 1st when you come to a stop. Intermittent. Also didn't always engage in reverse, also intermittent, but reasonably often. Also, after it was rebuilt, it always shifted funny...almost like a stick from 1-2, it stop accelerating almost like you were shifting a stick.

I'm a dealership vendor, water leaks/sunroof, etc. Had a former GM tech that now works at a Ford dealer look at it. Changed fluid/filter. There was a bit of glitter on the magnet, not awful. He removed and cleaned out the TCM and reset it.
Worked perfectly for a good long while. Didn't do that shifting glitch anymore, and still doesn't. But now doing the not downshifting into 1st at stops thing and slow to engage in reverse. Intermittent as before. Works fine otherwise.

It was rebuilt with what I assume was stock replacement stuff from Transtar. I replaced the same trans in my 15 truck 6 months ago with one from a buddy's tranny shop. It is beefed internals, billet converter, so I guess all improved stuff that normally fails.
Thinking I may have to do the same with the Tahoe, or let it go be someone else's, lol. But we like it.

Would you concur that it's on the road to ruin once again?
 
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NickTransmissions

NickTransmissions

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Hey Nick,
16 Tahoe 6L80. Was rebuilt by a GM tech 2 years ago. Had an issue not going back to 1st when you come to a stop. Intermittent. Also didn't always engage in reverse, also intermittent, but reasonably often. Also, after it was rebuilt, it always shifted funny...almost like a stick from 1-2, it stop accelerating almost like you were shifting a stick.

I'm a dealership vendor, water leaks/sunroof, etc. Had a former GM tech that now works at a Ford dealer look at it. Changed fluid/filter. There was a bit of glitter on the magnet, not awful. He removed and cleaned out the TCM and reset it.
Worked perfectly for a good long while. Didn't do that shifting glitch anymore, and still doesn't. But now doing the not downshifting into 1st at stops thing and slow to engage in reverse. Intermittent as before. Works fine otherwise.

It was rebuilt with what I assume was stock replacement stuff from Transtar. I replaced the same trans in my 15 truck 6 months ago with one from a buddy's tranny shop. It is beefed internals, billet converter, so I guess all improved stuff that normally fails.
Thinking I may have to do the same with the Tahoe, or let it go be someone else's, lol. But we like it.

Would you concur that it's on the road to ruin once again?
These kinds of symptoms have causes that can be one or more of the following:

- TEHCM
- Valve Body
- Torque Converter
- Internal Case Components

If it were me, the first things I'd do is drop the control body assembly, separate and test the TEHCM (or test the TEHCM for mechanical function using the Bosch Test Block while the vehicle was still present) then pull apart, clean and reassemble the valve body...Once each half has been reassembled, I'd test them both on the Sonnax vacuum test machine to see if there's wear/weakness in any of the valve trains. What I find when evaluating those two things would dictate my next moves.
 

YukCCR

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O'Reilly scan says "p0700 TCM Requested MIL Illlumination". Also just drove it in trailer mode, more than 5 times it would not shift up getting to almost 5k RPM at 55mph after slowing for 30mph corners. Have to lift to get it to shift. Didn't do it when going from a stop. VERY frustrating!
Got it back from the dealer today after having the manual/trailer switch assembly replaced. Will pull the trailer around tomorrow to verify that it's working correctly. If so, it's boat shopping time!
 

89Suburban

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Got it back from the dealer today after having the manual/trailer switch assembly replaced. Will pull the trailer around tomorrow to verify that it's working correctly. If so, it's boat shopping time!
What kind of boat?
 

CTX-SLPR

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One thing I've noticed is the wide variety of prices on converters, even one claiming "billet covers"
- The big names like Yank, Circle-D, etc. seem to want about $1300 for a billet converter from their websites and they are all higher stall than stock
- There are some more obvious names playing in the high $100's like Monster and ProTorque that seem to hold to stock stall if you want
- Then there's this section down around $500 like the reman on RockAuto or a RECON from Transendence

Not all of these list specs to look for the lockup clutch thicknesses as Nick suggested. How does one go about shopping for something that's a definite step up from the stock JMBX in terms of durability without going all in on increased power handling like a 2600rpm stall Circle-D?
 

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