8L90 GM 8 speed

[CaptArab]

Is it a POS?

Musing drivetrains for an engine swap.
The 6.2 / 10 speed is probably a better setup but these are half the price and plenty of power for my application. A couple more miles per gallon would be a sweet cherry on top.

Reading lots of issues early on regarding torque converters and shuddering. Not sure if all that can be remedied via tuning or if it's just a bad apple.

 

[dustingaunder]

What is your application?

 

[Kiba]

TCC shudder is the biggest issue with the 8L90. Very early transmissions had a seal issue between the clutch pressure plate and turbine in the torque converter which was corrected with a revised converter, but other than those initial converters the shudder was fluid related. There's been multiple revisions of fluid (3 now I think) to stop the tcc shudder, and the shudder issue appears to be solved with the latest fluid. However, if the thing had too many miles put on it with a shuddering tcc, the new fluid alone probably won't fix it as the tcc is likely glazed and it will need a new converter.

They will often shift very harsh from 1-2 and 2-1 at low speed especially when cold on the first shift of the drive cycle, that's related to the initial clutch fill time taking longer after fluid drainback while it was parked and is something you need to live with. A workaround is to manually shift into 1st and 2nd after the first start of the day to prefill the valve body before putting it in drive and taking off.

Other than those 2 issues, they seem to be pretty stout. There can be some occasional odd shifting behavior when driving aggressively with the factory TCM tuning that can be eliminated with proper retuning. I have several friends deep in the 10s and mid to high 9s at the strip with 8L90s and they haven't had a single issue even after several years of use. Also know someone that has one in their ZR1 that does several track days a year and hasn't had any issues.

 

[BoilerUP]

TSB 18-NA-355 is a necessity for the 8L90 to not shudder, which feels like a rumble strip.

/600whp ATS-V that gets regularly HPDE'd

 

[n2ishun]

POS,
Everyone with real power are going back to a T400 with a gear vendor.

 

[CaptArab]

What is your application?

80 series LC. Just needs to shove a 6k pound brick from the SE to western states and back a couple times a year, pull grades, get on the interstate with ease, pass, maybe pull a 2500 lb trailer on occasion, etc. 16-17 on the interstate would be fantastic.

Sounds like the 1-2 warm up jerk is just an ergonomics issue- that honestly wouldn't even phase me a bit as long as it wasn't going to cause failures.

Solid Intel @Kiba - is there an easily condensed rule of thumb for finding a good one?

For instance, "only a 2018 with < 45k, or if before 2018 less than 15k"?

That's totally made up but I think due to fluid recall years it might not be that far off.

Also, any tuner recommendations for the trans?
From what I understand, nixing the 1-4 slip is key.

Somewhat related, on the gen 5s (most likely L83), is it still best to just disable the AFM right from the start? Wouldn't mind the milage for my application, but not if it cost me in the long run.

 

[Kiba]

Regarding what years to try and find… Finding a 2018+ version is best as there was an update to the clutch apply pistons.

I’m going off memory here and could be wrong, but I think the final revision Mobil1 LV fluid was released late 2018/early 2019, so anything built after that would have had the latest revision fluid filled from the factory and probably never experienced TCC shudder. Anything built before the final revision of fluid was available probably experienced TCC shudder at some point, and without knowing the service history of the donor vehicle you would have no idea if the shudder was caught early enough to be fixed with only a fluid flush, or if it received a fluid flush plus new converter if the TCC was glazed from driving too long with a shudder condition, or if the previous owner didn’t notice/care and just drove it with the shudder. Worst case you might have to throw a new converter in it.

If you’re going to be towing make sure your cooling is up to the task. If you can keep the fluid at 200-220F max everything will be much happier.

Of course, if you want something simple and tough with overdrive and a lockup converter there’s always the good old 4L80/85E, but if you’re swapping in an application with a later engine and ECM then you have more work to do on the wiring and TCM side to get everything to play nice together. I’ve done plenty of 4L80/85 swaps over the years, but even the best ones are pretty “unrefined” feeling after driving the newer transmissions. The extra gears and ratio spread on the newer stuff is nice.

Regarding AFM… if you never want to roll the dice on an AFM lifter & cam failure down the road your best bet is to remove all the AFM related mechanical stuff (lifters, etc) during the swap and disable AFM entirely in the tune. It’s a total roll of the dice with the AFM stuff; I’ve seen brand new trucks have lifter failures at less than 3k miles, and other trucks go 200k+ on them without ever having an issue. The mileage change from disabling AFM is minimal in my experience, it’s usually about a 0.5mpg difference on trucks that see a lot of freeway commuting where AFM is usually active.

 

[BoilerUP]

Disabiling AFM isn't going to necessarily save you from the risk of having to do an actual DoD delete with lifters/pushrods/cam at some point.

Consider that future possibility an opportunity for BTR Stage 1 cam.

 

[CaptArab]

Yeah I just can't bring myself to do another 4 speed auto. Running 35-37" rubber, I'd end up regearing 3rds so the cost savings would be minimal. Plus the super short 1st of the 8 and 10 speeds would be super useful off highway.

Gen 5 or bust for me.

It also sounds like going ahead and doing a AFM/dod delete with brt or similar stage 1 truck cam upfront would be a good move.

Doing a Cummins swap on an old farm truck right now and it's going well, but for an adventure vehicle that spends long hours on trails, the comfort of the modern LT platform is appealing. The aftermarket makes it super easy as well- way less work than fabbing up and the hardware for the 900+ lb cummins. That weight + 300 lbs of steel bumper batteries and winch is a lot for Toyota axle and steering system.

Thanks guys - now at least I'll know what to price out with the local yards. Gotta have to crunch some numbers and make decisions.

Maybe I'm not asking the right people but the price premium for a 6.2 / 10 speed is like 50% higher than the 5.3 / 8 speed. Kinda overkill for a vehicle that came with 180 hp.

The 5.3 market makes it all much more financially viable.