L31/6L80e

[97Centurion]

Nice job! You've pioneered another "mod" for the GMT 400! LOL

What gear ratio does your truck have? I've read some comparisons on 4L vs 6L on the ls1tech forums and some guys say the fist gear of the 6L is too steep (maybe for a f-body?) I don't know.

I did recently buy a passenger 3500 van with the 6.0/6L90e/3.42, so I'm getting used to the transmission...my other trucks have the 4L80e/4.10 and I think I like the 4L80 more, but I think it's the rear gearing difference and the fact that the van is a big, heavy vehicle. The vans only come with 3.42, but the HD trucks came with 3.73s.

Also, what was the mileage on the transmission? Those seem to fail at around a certain mileage and send metal into the transmission and can cause a lot of damage. Maybe around the 150k mark? An aftermarket converter solves the problem though.

Let us know how you like it. Very interesante mod!

Thanks!!!

My truck has 3.73 gears. I could see why folks would consider 1st gear too steep, however, it may be personal preference. I think with my current combo, it's just right for daily driving, considering the weight of a crew cab and it being an L31. I have a '14 Silverado, also with a 6L80 and 3.42 gears...the difference between the two (aside from the obvious) are night and day when it comes to normal driving. I feel like the '97 makes better use of it's new first gear getting up to speed. So, I do agree it's gearing difference. I just remember when the 6L's were introduced, one of the hypes were how they were geared and take-offs were much much faster off the line. Again, maybe personal preference and/or depending on one's build.

Most people won't believe this, but my 6L has 195k on it (I know, crazy right?!). The guy I bought it from assured me it was maintained properly and it shifted through all gears with no problems or slippage. The L83 it was mated to became a victim of the DoD lifter failure, locking up the lifter and trashing the cam. Shortly after bringing it home, I pulled the pan and filter, and to my surprise, the fluid was bright red and the magnet was fairly clean. Of course, I was releluctant until recently when I finally drove it a couple days ago and confirmed he was right.

 

[618 Syndicate]

Sub'd. I gotta do something about highway driving in my dually, I like to run 80+ and the 4L and 4.11 rear end put the motor over 3500 rpm. Maybe a 6L is the answer.

 

[Supercharged111]

It'll only drop about 200 RPM if I had to guess. You got from a .75 to what, a .67 OD?

 

[stutaeng]

Thanks!!!

My truck has 3.73 gears. I could see why folks would consider 1st gear too steep, however, it may be personal preference. I think with my current combo, it's just right for daily driving, considering the weight of a crew cab and it being an L31. I have a '14 Silverado, also with a 6L80 and 3.42 gears...the difference between the two (aside from the obvious) are night and day when it comes to normal driving. I feel like the '97 makes better use of it's new first gear getting up to speed. So, I do agree it's gearing difference. I just remember when the 6L's were introduced, one of the hypes were how they were geared and take-offs were much much faster off the line. Again, maybe personal preference and/or depending on one's build.

Most people won't believe this, but my 6L has 195k on it (I know, crazy right?!). The guy I bought it from assured me it was maintained properly and it shifted through all gears with no problems or slippage. The L83 it was mated to became a victim of the DoD lifter failure, locking up the lifter and trashing the cam. Shortly after bringing it home, I pulled the pan and filter, and to my surprise, the fluid was bright red and the magnet was fairly clean. Of course, I was releluctant until recently when I finally drove it a couple days ago and confirmed he was right.

My buddy drives a '11 2500 HD work truck and the 6L90e made it to almost 300k. His company paid for the rebuild from the dealership for a whopping $5k or some crazy number like that. (The rebuild kits for those units are spendy compared to the 4Lxx units.) By brother's BIL '14 1500 6L80e also bit the dust at a little over 120k, but he bought the truck used shortly prior, so no telling how it was treated before.

In my limited experience (and again I think it depends on the axle gearing) it seems like the more gears on a vehicle, the more it likes to downshift. My wife's T&C 6 speed likes to downshift on acceleration (empty!), which I kinda find annoying, LOL. Better axle gearing usually means the engine can hold the torque demand better before down shifting to a lower gear to get the RPM higher.

Also, in your case the L31 makes it's torque at a lower RPM, so that's part of what you are describing on the comparison.

BTW, are you planning on swapping the shift lever with the "+" and "-"? I believe I've seen that swap here on these 400 trucks...Are you able to use the tow/haul mode function?

 

[sync]

Yeppers, as stated, once complete, I'll have everything together and do a follow up post.

As far as the shifter in general, yes it does work. It pops right onto the shifter linkage. My 6L did not have any of the miscellaneous bracketry, so I fabricated my own shifter bracket using 1/8" angle iron and cutting off the C-shaped part (pictured) of the 4L's and welded it together.

So the PRND321 is the same?

 

[97Centurion]

Sub'd. I gotta do something about highway driving in my dually, I like to run 80+ and the 4L and 4.11 rear end put the motor over 3500 rpm. Maybe a 6L is the answer.

Thanks!!!

I would most definitely think your gearing would chip your rpm down more effectively. The 6L would bring your rpm down a few hundred, but, I can say the 6L will more efficiently make use of your motor's power band. Plus, at highway speeds, you'd have 2 overdrive gears!

 

[97Centurion]

My buddy drives a '11 2500 HD work truck and the 6L90e made it to almost 300k. His company paid for the rebuild from the dealership for a whopping $5k or some crazy number like that. (The rebuild kits for those units are spendy compared to the 4Lxx units.) By brother's BIL '14 1500 6L80e also bit the dust at a little over 120k, but he bought the truck used shortly prior, so no telling how it was treated before.

In my limited experience (and again I think it depends on the axle gearing) it seems like the more gears on a vehicle, the more it likes to downshift. My wife's T&C 6 speed likes to downshift on acceleration (empty!), which I kinda find annoying, LOL. Better axle gearing usually means the engine can hold the torque demand better before down shifting to a lower gear to get the RPM higher.

Also, in your case the L31 makes it's torque at a lower RPM, so that's part of what you are describing on the comparison.

BTW, are you planning on swapping the shift lever with the "+" and "-"? I believe I've seen that swap here on these 400 trucks...Are you able to use the tow/haul mode function?

My wife has a 2020 Traverse with a 9 speed. It's crazy how much it downshifts just to speed up a bit. GM did a very good job (in my opinion) on this trans, as you cannot feel it shifting at all. It almost feels like a CVT trans. Thing is no slouch either!

For the shift lever, I do in fact plan to change it to the one mentioned later on. I bought a better condition cab to swap with (tree fell on mine) and scored a 14 bolt sf I want to get installed first.

 

[97Centurion]

So the PRND321 is the same?

Not quite. The module's monitoring software says 2 and 1 are in 1st gear and 3 is 2nd gear. I'm still trying to figure the software out to see if that's programmable. I'm probably not going to have much time until the weekend...my job is very demanding this week, but it will give me time to read, research, and contact powertraincontrolsolutions.

 

[Supercharged111]

Not quite. The module's monitoring software says 2 and 1 are in 1st gear and 3 is 2nd gear. I'm still trying to figure the software out to see if that's programmable. I'm probably not going to have much time until the weekend...my job is very demanding this week, but it will give me time to read, research, and contact powertraincontrolsolutions.

You're going to have to math this one out. If you can match the pivot radius of the 6L trans to the 4L shifter, you should be able to get it down to 6, 5, 4, 3, but I don't see a perfect solution for this one. Maybe live with it as is and just use TATD for manual gearing?

 

[Grimpala]

Not to hijack your thread, but what are thoughts on running a 6L80e behind an L29 using a 0411 computer to run things? Can it even be done?