2017 silverado 6l80 help after a fresh rebuil

[bapst43]

I had my 6l80 rebuilt about 4 months ago. We did all the upgrades zip kit new pump/bellhousing converter. Shortly after the rebuild I pulled a trailer with my 68 pickup on it around 600 miles with the tow haul on and it worked like normal. A couple of weeks after that it started to sound like rumble strips driving on the highway while the engine rpms where low (lugging the engine) I also did the thermostat change and my temperature rarely get to 140 now but it's winter but I drive 30 miles on the 75mph highway to and from work and this morning only got to 115 degrees. So it seems like it chatters or lug worse until the fluid temperature gets above 90. If I manually shift it with the tap shift and don't lug the engine I can keep the rumble strip sound and feel from happening. If i leave it in manual 5 it doesn't do it hardly at all but i get a knock code. I don't know why happened over the short time that made the change other than that was the end of summer and now it's winter and the fluid I alot colder. Cam anyone help with this? Thanks

[TheMechanic]

Need a tune file and a run log. Difficult to diag without those. Maybe try an ever so light push on the brake pedal to disengage the TCC and see if it goes away. Need to log converter slip.

[bapst43]

I will try to put a log file on tonight

[TransGo Robert]

A log of course would make it easier to say for sure, but most of the time this happens because they use a converter without the OE woven carbon lock-up clutch lining. In those cases, adding a bottle of Ford XL-3 limited slip additive to the transmission usually will get rid of the shudder.

[TheMechanic]

A log of course would make it easier to say for sure, but most of the time this happens because they use a converter without the OE woven carbon lock-up clutch lining. In those cases, adding a bottle of Ford XL-3 limited slip additive to the transmission usually will get rid of the shudder.

That's not differential friction modifier is it? Never heard of it for transmission specific.

[TransGo Robert]

That's not differential friction modifier is it? Never heard of it for transmission specific.

Correct it is the differential friction modifier. Works like a charm in transmissions when you have a squawk or a shudder. Transmission guys have been using the stuff for 30-40 and surprisingly it still works fine and cause no damage in modern transmsision with TCM and other electronics in the unit.

[bapst43]

I'm not sure if I'm doing this right or not but here is a log. 12-24 ride after changes to psi and zeroed tcc slip in 1-4 gears.hpl

Thanks for any help!

[TransGo Robert]

I'm not sure if I'm doing this right or not but here is a log. 12-24 ride after changes to psi and zeroed tcc slip in 1-4 gears.hpl

Thanks for any help!

With a tune set to lock-up fully like that it is doing what it is asked to do. The engine runs real good so that's not where the shudder/noise/vibration comes from. Most likely it is doing this during the cylinder deactivation mode (can't tell for sure because the relevant engine PIDs were not logged for that). If that's when it happens (easy to tell it will not do it in TOW/HAUL mode) then either disable AFM aka DOD in the tune, or get the converter command back to stock so that it can slip 40 RPM or so and absorb the vibrations.

[bapst43]

I have the afm off. It shudders when the engine rpms are low and it shifts to early and lugs. If I run it in manual and shift it when I want it does fine. I have tried to change when I shift into 5th and 6th so the rpm is higher but haven't found the magic number yet. Also if it would downshift instead of lugging and shuddering I think that would also help. The transmission did fine until it got colder and while the transmission fluid temperature is lower it shudders more too.

[hjtrbo]

If that additive doesn't work then you're going to have to tune around it. You can go back to your slip tables to introduce so at low rpm. If the tc frictions aren't designed for it then you have few choices left.

[hjtrbo]

Also, I don't know what people obsession is with running transmissions so cold. There is temperature based viscosity modifiers in behind the scenes that come into play with cold temps that make tuning harder. I'll dig the numbers later so we know the range GM designed it for.

[TransGo Robert]

Also, I don't know what people obsession is with running transmissions so cold. There is temperature based viscosity modifiers in behind the scenes that come into play with cold temps that make tuning harder. I'll dig the numbers later so we know the range GM designed it for.

it sure is an obsession nowadays with the internet machine amplifying the echo chamber where low fluid temp gets promoted all the time. Many people still think it is like the 60s when fluid temp above 160 F made the ATF degrade. ON this one I see no sign of shudder at all in his log, my suspicions is that what is felt is coming from the engine. Getting the converter to back to slipping as intended around 20-30 RPM would most likely solve the issue, but looking at all the engine data would help rule out any serious issue there first.

[hjtrbo]

Spot on Rob. I aim to run my transmissions at 70-90 degC using the deralle thermostat block for quick warm-up, and a large cooler with temperature switched Thermo fan.