6L80 Heat Related Symptoms

[CTX-SLPR]

IF you have it already set up with HPT you should go thru your torque converter settings
and shift scheduling to get rid of some of the crazy crap gm did with those settings

Already done that including a reflash after I put a ZipKit in the VB. I smashed the screen on my tuning laptop and I've not fixed it or moved on yet as I have it setup on the bench for testing my Riviera swap out along with the Microsquirt trans controller.

 

[CTX-SLPR]

@NickTransmissions, do you think the VB is bad and the valves are binding and a new VB will fix it or the unknown reman TC is coming apart and it's a total clean and redo?

Thanks

 

[NickTransmissions]

Regardless I get shifting weirdness at around 195º. What are the likely culprits that start sticking with heat? Things are fine at lower temps like today a 1hr drive in the mid 50ºs and misting was fine with trans temps in the 140ºs. Yes, I'm a pretty relaxed driver but I bought this vs. a minivan because I need to tow and I can't keep it acting normal unloaded so no way I'm going to hitch something to it even with a 40k cooler in the nose. Something is getting hot and acting up and I'd rather try to troubleshoot it before throwing $3.5k at a reman Street Smart unit.

Assuming the above is a fair and accurate description of your current drivability symptoms, Im guessing you have a worn out pressure regulator valve, especially if the 'weird shifting' occurs at multiple points in the drive cycle once the vehicle and transmission reach operating temp.

@NickTransmissions, do you think the VB is bad and the valves are binding and a new VB will fix it or the unknown reman TC is coming apart and it's a total clean and redo?

Thanks

The TC can be playing a role but unless you have shuddering, it's not likely. Valve body may or may not be worn - impossible to say without vacuum testing it.

Have you taken it for a drive with a bidirectional scan tool and/or HP Tuners plugged in showing what's happening once the transmission and torque converter once the unit starts mis-behaving? Does the vehicle have any engine/engine management related or electrical issues?

 

[CTX-SLPR]

Not done a drive with the scanners hooked up since all the maintenance, just last summer when things got real bad for the first time. The shifting weirdness is largely related to decelerating to a stop, vehicle comes almost to a stop then the trans downshifts the final time resulting in it feeling like it's trying to push through the brakes for a moment. This happens not infrequently but not constantly when hot. The really unnerving one is when you let off the brakes from a stop and it revs then lurches into gear. This is much rarer in frequency but will happen for sure on a 15-20min drive in traffic if it's up to 195º+. All of this centers around lower gears, never had a problem in the upper gears even before doing the Zip Kit and finding a missing check ball.
Thinking about it, the decel issue could be the converter trying to stay locked too long (I have 3-6 gear TCC still on) as from memory it's worse under harder braking. The TCC is up in the pump section which I've not been through beyond watching an analog gauge under the wiper on a 20min drive test drive just before doing the Zip Kit.

 

[NickTransmissions]

The really unnerving one is when you let off the brakes from a stop and it revs then lurches into gear.

This sounds like torque converter to me; I believe the 8-speed units are/were doing this or similar behavior, causing accidents...IIRC, the basis of the class action suits pending against GM for those converters was the sudden onset of violent, back-breaking shifts.

I'd get it to a shop asap if you're not able to fully diagnose and, if necessary, yank it out (assuming it's not already there). I think the TC is in the process of failing but that's just speculation from someone that isn't there and no data...Meanwhile drop the pan if you haven't already done so and you're willing/able to - see if there's anything at the bottom.

 

[CTX-SLPR]

When I did the Zip Kit in the fall there was some friction material in the pan after only a few (<5) thousand miles on the fluid which was more than I expected. No metal sparklies but the magnet was slightly dirtier than the main pan.

I'll drive it carefully the few times I have to get to class and such till I can get my backup car back from the family I loaned it to while I fix the front main seal on their truck.