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I own a 1991 gmc 2500 454/4L80e truck with 37k miles. I’ve recently run into issues with the truck going into limp mode every time I drive it. Essentially what happens is it will start and drive around fine(other than hard shifts) and have all gears for the first 15-20 minutes of driving. As soon as I come to a stop after that timeframe I will get the CEL illuminated and the truck will be in limp mode with codes; 24. VSS Signal 73. Trans Temp 85. PROM Read fail 87. PROM I’ve already investigated the pass through and it was leaking. I’ve cleaned it out and tried with no difference, from the bottom of the truck the wiring looks pretty good. At this rate I don’t know where to go in terms of diag, wondering if anyone else has seen this issue? , also any suggestions are more than welcome
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
Well, seeing as how I can't find much on this subject no matter what forum I go to, why not try to start the discussion here and see what kind of following I can get and see where we end up. If you're reading this thread, chances are you have thought about modifying or swapping out your current transmission in your 2014+ GM truck. In my case, I don't mind my 6L80 in my truck. It does fine for what I do right now and it's holding up just fine, but I think the big issue is when you start to search for big power (like I'm starting to do), that 6L80 is not going to hold very much (or so we think). Now, let's all face it. We've seen posts after posts, comments after comments, photos, videos, etc. of guys with built motors with turbos or prochargers shooting down the quarter mile in search for the best time on these 6L80s. Some say they're completely stock, others have them built, and we all ask ourselves the same question: Reliability. How well are these transmissions going to hold up to the abuse on the track? Especially if you want to make it a fast street/strip truck and drive it back home to the garage afterwords. We know for a fact that 6L90s can hold quite a bit of power. Even though I've mostly seen it in Camaro ZL1 applications, there is a guy on YouTube (GuitarmaggedonZL1) who is running a stock 6L90 on stock converter making 1000HP (give or take on an unloaded dyno) and the transmission hasn't puked all over the ground just yet. (Exaggeration, I know.) So, needless to say, a 6L90 swap sounds nice, at first... After you figure the extra length and weight (and in my case, relocation of the transfer case and getting custom driveshafts made), it starts to look a bit unpromising, but still not out of the ball park yet since it will be able to handle the power some are seeking, but where these newer transmissions lack significantly if you want to do boosted applications at the track (or even just launch control on N/A), no one has developed a transbrake. Very, very few forums are talking about this, and only one video exists of a guy in his BMW testing out a transbrake on a 6L80/6L90, and who knows how reliable it is. So, now, you start to think: Well, gee. What can I do now? How about a TH400 or 4L80e swap? So far, I've seen few posts on that as well. No one is talking about it, and I think the biggest problem people seem to be facing is the new PCM: E92. Also possibly the fact that the TCM on the newer transmissions is inside the transmission and whatnot, but whether that plays a part in this, I don't know yet. Now, adapting a TH400 or 4L80e can be done (most likely with a different bellhousing since the bolt holes are in a slightly different spot), but you run into the issue of getting it to speak/cooperate/communicate with the new E92, which I don't think anyone has tried. The only video I've seen of anything working in this application was on a 1320Videos video with a Nova where they were using an LT4 long block (built motor to 388 C.I.) and twin turbos, and it had a powerglide in it. Don't know if it was a manual valve body or computer-controlled, but what I do know is that they used the factory computer to run the DI injection system and piggybacked the rest to an MS3 Pro. After dealing with some issues, they were able to make that thing boogy to a 9 second pass at 148mph. So, these engines have potential to haul ass, but we just haven't figured out how to crack the system. So, at this point, I'll just leave what I've discussed here and see where the thread goes from here, and I'm hoping people chime in and vendors are watching/listening. Even though the demand isn't hot for it right now, there's going to be a surge for good transmissions when people can buy these trucks/cars/motors/transmissions for pennies on the dollar. Unfortunately, I feel like we'll have to wait that long in order to see results, but oh well. Just to give you guys an example: In the next year or two (2019 or 2020), I'd like to go turbo with my truck. (Doing all the supporting mods before going there minus built bottom end until I see where I can get with stock bottom end before sending a rod through the block or oil pan) Ideally, it'd be best to have a transbrake in that application with 2-step, but can't do it on the new transmissions. So, 4L80 seems to be the option, but I can't do that either because no one supports adapters or harnesses to make them work with the new motors/ECUs. That's the boat I'm in. I like to research everything before I go whole hog into something. Risk assessment, I guess.