4l80 issues, heat and no lockup.

[Brendan Corr]

Hello all, i have a 2002 2500hd 6.0/4l80 combo. The truck is blackbear tuned and has been for nearly 10,000 miles. I recently converted the truck to 4x4 with the drive train out from under a 2007 classic. The transmission was a GM reman with little to no miles on it. I dropped the pan, changed the filter and filter o-ring. Then filled with some dex6. The other day i was driving up a fairly steep grad (i-70W), truck was preforming normally trans at around 190-200F when all of a sudden it started shifting crazy hard and getting warm. I scanned it and pulled the dreaded P1870 transmission component slipping No CEL or any other codes. The trans will shift fine when cool until about 175, then it goes back into like a protect mode and will heat over 200F in a couple miles (still have all gears and shifts during this, just very very hard shifts and no lockup.). I have all gear shifts except lockup even when cool. The fluid is still bright pink and has less than 3000 miles on it with no burned smell. My current plans are to pull the trans, change converter and the trans cooling lines as i'm sure the rubber flex joints have collapsed as well as flush both the aux cooler and cooler built into the radiator. Is there anything else i should be doing, or anyone with a similar problem that they've resolved? Any input will be greatly appreciated.

-Brendan Corr

[carkhz316]

(I posted this in your other thread, but copying/ paste here for visibility)

 

It was common in the early 2000s 4l80 trucks for the converter clutch piston to crack and cause a loss of lockup and P1870 code. However, I've seen the issue persist into at least the '06 model year (last one I rebuilt was in a 2006), so I don't think it was ever rectified. It sounds like you are experiencing the same issue. The way I diagnosed it was using a bi-directional scan tool to command TCC lockup and only obtaining about a 25-50 rpm drop (instead of the normal 2-300). The hard shifting is when it goes into limp mode due to what it detects as trans slippage (P1870). This happens after so many minutes of driving, or drive cycles, independent of most any other factors. The reason why it's running hot is simply a byproduct of the TCC staying unlocked.

[Brendan Corr]

3 minutes ago, carkhz316 said:

(I posted this in your other thread, but copying/ paste here for visibility)

 

It was common in the early 2000s 4l80 trucks for the converter clutch piston to crack and cause a loss of lockup and P1870 code. However, I've seen the issue persist into at least the '06 model year (last one I rebuilt was in a 2006), so I don't think it was ever rectified. It sounds like you are experiencing the same issue. The way I diagnosed it was using a bi-directional scan tool to command TCC lockup and only obtaining about a 25-50 rpm drop (instead of the normal 2-300). The hard shifting is when it goes into limp mode due to what it detects as trans slippage (P1870). This happens after so many minutes of driving, or drive cycles, independent of most any other factors. The reason why it's running hot is simply a byproduct of the TCC staying unlocked.

Thank you, this is what i have been suspecting due to the other gears all applying quickly and firmly like normal before it goes into limp.

[Formulabruce]

I would upgrade that transmission cooler. Easy to do and you can fit one twice the size up front. Tranny temps should not go above 160 when empty. Automatics begin to wear parts when trans temps are over 200.

[Brendan Corr]

3 minutes ago, Formulabruce said:

I would upgrade that transmission cooler. Easy to do and you can fit one twice the size up front. Tranny temps should not go above 160 when empty. Automatics begin to wear parts when trans temps are over 200.

those temps were while climbing a 6% grade for miles. When im down in Texas for the summers, it wont get up there unless towing a semi heavy trailer.

[Brendan Corr]

I ended up changing lines, flushing Rad cooler (seems quite restrictive) and replacing the aux cooler with one double the size. I got lockup back slowly but weak. The trans still heats quickly, but slower if i can keep it in lockup. i have a reman converter for it and plan to install it next weekend, Does it still sound like the converter. 

[carkhz316]

Yes, it still sounds like that, but can't say with absolute certainty without diagnosis.

[Brendan Corr]

I ended up bypassing the factory cooler in the radiator all together because I couldn’t get over how hard it was to blow shop air through. Immediately the transmission acted normal but lockup was weak you could watch it slip on the tach. My dad and I ended up dropping the transmission and changing the torque converter. While we were in there we replaced the rear main seal, oil pan gasket, transfer case output seal, and the gasket between the transmission and transmission. The difference is night and day, the truck locks up and stays locked up even in gentle grades where it wouldn’t before (I don’t think this TC was ever good, it came on the transmission from the parts truck) all while keeping in mind, my 22x12’s and 33’s weigh almost 100lbs a tire. Thanks for everyone’s help.