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Found 12 results

  1. Hey guys, I did the thermal bypass conversion to active by pass on my 2018 8L90. Did a step by step video because I hadn’t seen anybody do an actual full replacement video nor had I seen one on a 8 speed. Trans runs about 45 degrees cooler now. Check it out and let me know what you think. It’s the exact same procedure on 6 speeds just mounts different on the transmission.
  2. My 2019 Sierra with 12,00 miles under warranty was diagnosed by the dealership. Was told the valve body need replacement that was 7 days ago now I’m being told a replace valve body is not available and they don’t have an eta for the part. Primary issue is the torque converter clutch disengages every 5-10 seconds at highway speed, in town it is much worse. Secondary problem torque converter clutch disengages the vehicle shimmies also at low speeds has a harsh shift.
  3. Not sure if this has made rounds on this forum yet, but it was brought to my attention at work as we have a 2016 5.3/A8 in for this concern right now (we've done them in the past but its been a month or two). I've highlighted in red the big change, GM is no longer replacing converters based on their findings on returned warranty units as it can still come right back. The triple flush has been dropped for now, just a flush and re-evaluate. It does appear they must be on to something that is a better fix as they are working on one to be released Q1 2019. Looks like they will continue to only flush/fill them for now. This does apply to ALL 8 speed applications, both 8L45 and 8L90, EXCLUDING the new T1 1500 trucks. Stay tuned...
  4. First post, been a lurker for 3 yrs...2017 High Country w/ 101K. Lost 6,7,8, gears and truck wont shift past 5th at all. Similar symptoms to others, hard hesitation then super high RPMs (low gear limp mode). Dealer inspects and says fluid is so gummed up the valve body, solenoids and some other sh*t is "stuck" and there is metal everywhere. Yep, had the torque converter issue at 30K, with dealer flush. $5K for a new trans with a better warranty than the stock, 3yr/100K...wtf. Apparently any "updates" GM has made will be in this shiny turd of a sh*t show. Anyway...after this disaster, I'm in prevention mode...new fluid after the first 10K, then every 20k (trans, diffs, transfer). Oil every 5k, this 8L90 sucks azz.
  5. I have a 2017 Chevy Silverado 4x4 5.3l V8 with the 8 speed transmission. I already flushed out my transmission and filled it back up with the Mobil 1™ Synthetic LV ATF HP blue label. The question is, do i also use the HP fluid for my transfer case? Or do i need to use just a standard ATF fluid instead. I cant seem to find a straight answer on this. The owners manual states to use DEXRON®-VI Automatic Transmission Fluid. Would using regular ATF in the transfer case and HP ATF in the transmission cause any issues? Thanks in advance!
  6. Earlier in the week my check engine light came on and I saw the P0700 and P0711 which lead me to Transmission Fluid Sensor issues and people having to replace them. I started monitoring the sensor and noticed it didn't fail like most other people but it takes an awful long time to warm up only peaking at 150F whereas previously it seemed to always be near 200. It took about 45 minutes of driving to get into the 140's and only passed 150F after another hour of driving after that. As I learned the thermostat is only supposed to open up at 192F so I believe mine is stuck open. I will see if the dealer will give this under warranty but I'm curious, anyone do thermostat deletes and regret it? From what I read, the TCM wants 200F or close to it for better shifts and this is why the thermostat is there in the first place. On the other hand, living in a warmer climate where it doesn't usually get below 40-50F, could leaving this thermostat open extend the transmission life?
  7. I got the dreaded P0700 & P0711 on Monday on a 2015 GMC Yukon Denali. Cleared the code and it came back. MIL hasn't iluminated yet so I'm waiting on another drive cycle before I schedule an appointment with the dealer. In the meantime I wanted to understand the conditions of P0711. GM has a great PDF but I can't quite understand it. https://gsi.ext.gm.com/gmspo/mode6/pdf/2015/15OBDG08A Transmission Diagnostics.pdf I don't quite understand how to apply the table to the conditions. Further to add confusion, my scan tool is reading -40F for TFT although in tow mode my transmission temp reading hovers between 125 and 150. I did watch it once and see it dip to 100 flat from 125-150 for a brief moment so I imagine its just a flaky sensor but I'm more curious about what triggers this based on those conditions.
  8. First thread on here, hope it helps people. **!!** DISCLAIMER **!!** Yes i know this is an 8 spd and its supposed to feel different than other automatic transmissions. AND Yes, I know these transmissions had a lot of issues out of the factory. **!!** DISCLAIMER **!!** Looking to find out information/recommendations for full fluid flush (cooler and all) and filter change for 2016 silverado 1500 with 6.2L and 8spd with max trailering pkg (which i think makes it an 8L90, havent confirmed yet) with almost 90000 miles (maint schedule from chevy for 2016 says trans/tfr case/diffs fluids due at 90k). I have a hard shift from 1 to 2 at very low speeds sometimes (especially when cold, but that makes sense because fluid dynamics), basically parking lot driving. I also have a weird deceleration when up to temp when taking off from a light less than 1/4 throttle, going from 1 to 2. Its almost like its slipping too long between 1st and 2nd. My body physically moves forward due to what feels like pushing the clutch in during acceleration. No banging or loud noises, just noticeable loss in acceleration. Just bought the truck at 88750 miles. If it matters, it has had PCM warranty reflash in the past, not sure based on garbage maintenance records if a flush had ever been performed. What I know: Dealership quote (Milwaukee, WI area) before 10% discount: - Gasket $36.21 - Filter $30.17 - Fluid $170.20 (represents 20 qts., *not sure if capacity or thats just how much they use when flushing*) - Labor and shop supplies $546.29 (this price makes me think that it is more than just a flush, like they are opening the system and forcing fluid and or cleansers through all components that touch trans fluid to make sure its fully flushed/cleaned. if just flush where they hook up to machine, this is such a damn rip off) Transmission fluid I am supposed to use to avoid shuttering or issues due to moisture absorption that was initially experienced according to GM TSB# 18-NA-355 (*PLEASE LET ME KNOW IF THIS IS OLD TSB#*): - (*HAS TO BE WITH BLUE DOT, NOT BLACK DOT) Mobil 1 Synthetic LV ATF HP It has never had the fluid changed before to my knowledge I'm trying to figure out what the latest GM factory procedure (either with a TSB# or whatever work order code is used) is so that I can communicate to multiple dealerships nearby so I can get pricing on actual same services. Here is the link that describes it a lil more and shows the fittings that they put on transmission for flush: https://gm-techlink.com/?p=11127 And here is another about the TSB for fluid (this one is more recent than the one above): http://gmauthority.com/blog/2019/08/tsb-seems-to-fix-8-speed-automatic-gm-transmission-problems/ I plan on getting a fluid sample of the transmissions fluid from dealer prior to changing so that I can send it out and get it tested so I have a record. (I will post the results of tests here when I get them). I got my free test sample bottles from Blackstone Laboratories (If you or your friend has an in with GM engineering and/or happens to know the pass/fail criteria that they use to decide whether or not to cover transmission or torque converter replacement, please let me know. I'd like to know what to look out for when I get my results from fluid testing) This is the most expensive thing I have ever purchased, i have extended warranty on it just because I'm worried about the transmission and obviously all the electrical doodads that new vehicles have nowadays, I just want to make sure I am taking care of it correctly. Would love to hear from seasoned GM certified techs and/or ASE master mechanics/techs and/or GM Engineers. Also please chime in with prices you've experienced including general location you're from so I can get an idea if this dealer is trying to rip me off. (so far the only thing I dont trust is the labor/shop supplies in the quote above, depending on what the procedure is)
  9. Long time reader and first time poster. I recently started to have vibration issues with my 2015 Yukon Denali. It started after the last scheduled oil change and tire rotation. I noticed the vehicle vibrating quite often. I started paying more attention to it and realized there was a shudder in-between gears that became worse as the transmission warmed up. Took it to the dealer I purchased it at and it was a bit of a fiasco because they were backlogged and ended up taking it to another dealer who performed 2810175 (updated TCM with latest calibration and relearn). They handed me the vehicle and said all fixed. Took the vehicle home and it seemed to be ok but started noticing the shudder again. One question is after this, is it expected that there should be a relearn time for X miles while its relearning the shift adapts/pressures? Is there an estimated number of miles for this? It seems to shudder less often but when it does it seems worse than before. I've only driven it about 60 miles since the recalibration. I'm fully aware of PIP5337 and asked them about this but they said the TCC was not bad. The vehicle was purchased June of 2015 so its definitely manufactured before November of 2015 which PIP5337D mentions. As I drive it more and more, I feel less of a transmission shudder but more road vibration than I felt in the loaner 2016 Yukon SLT or my wife's Kia Soul. I'm wondering if its possible they rebalanced improperly. The road vibration seems to be at lower speeds. At higher speeds it is better but may just be the quality of the roads I am driving on at lower speeds. I do notice the TAC jumps about 100 rpm during most shifts and not sure if this is normal. It seems to do this when the TCC speed should be 0 (around 2000PM) shifts. I realize it would not be fully locked under 1600RPM. At this point, I am not really sure if I am just paying too much attention to every bump on the road or if there is an actual issue. Are there any objective ways to determine if there is an actual issue and express that in a way that will not completely annoy the dealer? I have already had to pull this vehicle from one dealer because they were so backlogged it would have been in the lot sitting for repair for 23 days. With that said, they planned on doing a tear down on it to inspect and thought it was the TCC. Any help or guidance is much appreciated. Thanks!
  10. Hello all! First post here! What brought me here was the 8l90 torque converter lockup shudder issue. Most times I'd just take this truck to the dealer and let them sort it out, but as it's out of warranty, this is not something I'd like to pay >$600 to repair (this price was quoted to me for the flush and filter change). After talking to a few service advisors I've found that each of them planned on using a different solution to attempt to alleviate the shudder. The first was going to proceed via one of the bulletins and do a triple fluid swap and filter change, the others were just going to do a standard flush and fluid swap. I plan on owning this vehicle for another few months until the 19's become a little more negotiable but cannot stand to let this shudder go on that long and am a bit worried about destroying the torque converter in the process and washing a whole bunch of parts down into the transmission. So.... my question is if anyone has performed this fluid swap themselves, if it alleviated the issue, and if the filter change is necessary? I saw that many of the Corvette guys were swapping to the Mobil 1 fluid with some success, however, I didn't think this was as much of a fluid performance issue as it was a suspended clutch material / dirty fluid issue. Any help would be greatly appreciated!!!!!!
  11. 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.
  12. As many truck and SUV owners know, the performance of the transmission is a big part in how confident you feel behind the wheel. While only a single part in a complex powertrain, the transmission is the glue that links an engine to the road. When the transmission hesitates, the entire vehicle’s performance suffers. A great vehicle needs an equally great transmission. After only a few minutes behind the wheel it became obvious that shifts are quicker and smoother than the past generation 6-speed. Having two more gears allows the engine to stay in the sweet spot of the RPM range more often. Tip into the throttle and with no drama the 8L90 quickly snaps to the right gear. However, the most noticeable change is how well shifts are managed by the faster next generation transmission controller. Dependable and crisp transmission performance is a benefit in any situation. A slight bump in fuel economy is the icing on the cake, allowing for a +1mpg bump in fuel economy. Under full throttle we found gear changes effortless, quick, and solid. Under light throttle we could barely notice the vehicle had shifted at all. Where the past generation 6-speed sometimes gets confused or doesn't shift as cleanly as we’d like, the new 8-speed was always seemed on point. Unfortunately, we're slightly surprised to see that manual shifting with the 8-speed hasn't changed. Commands to select a specific gear using the shifter stalk are still only a suggestion, with the transmission controller having a final say. In our short test, shift requests sometimes took seconds if the truck didn't agree with the gear we requested. We drove an 8L90 equipped 2015 Sierra Denali and Yukon Denali on urban streets during rush hour. We did not get an opportunity to measure fuel economy. While only available with the 420-horsepower 6.2L EcoTec V8 during model-year 2015, expect this 8-speed to be available in the rest of the full-size truck and SUV line in the near future. When we have an extended amount of time with another 8-speed truck we will report back with fuel economy figures and more driving impressions.
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