Sign up for FREE! Become a GM-Trucks.com Member Today!
In 20 seconds you can become part of the worlds largest and oldest community discussing General Motors, Chevrolet and GMC branded pickups, crossovers, and SUVs. From buying research to owner support, join 1.5 MILLION GM Truck Enthusiasts every month who use GM-Trucks.com as a daily part of their ownership experience.
So, not sure if I'm the only one who has this issue at 130,061 miles but for some reason one night my truck was shifting pretty harsh, keep in mind this is the first time it's done this. I was far from home so I just drove home because I didn't have the money to have it towed nor was I going to leave it out here for looters to break into. Drove it home and just down the street from my house the truck just did not want to drive. It wouldn't go into Drive or Reverse, had to push her heavy ass home. Next day I decided to see if she'll budge and long behold it actually went into gear and I was able to move it where I usually park it. I did not take it for a drive afraid it would happen again. Anyone know what could've caused it to just stop going into gear and then now it will. Seems odd to me.
I've read a bunch of different posts on transmission issues and the like, but I'm simply looking to do a fluid and filter change. My truck is a 2015, 5.3, 6 speed - I'm assuming it's the 6L80, is that right? I know it takes Dex VI, just not sure how much. 75k, and it's not been changed yet. Plan on doing both diffs, transfer case, and transmission.
I've got Mobil 1 75/90 for both diffs. I know I need 2 qts of Dex VI for the transfer case, just not sure how much for a fluid/filter change for the transmission. I'm assuming synthetic is preferred for the transmission and transfer case?
Possible cause of DTC P0777 for a 6L80 transmission -
especially after a re-build, upgrade, or maintenance of the valve body
(a chapter from my upcoming book, "Learn from my mistakes!")
Here's the context:
2007 GMC Yukon Denali 6L80 Transmission (Early, 1st Design, original equipment, no prior work or refurbishment actions taken on this transmission/valve body/TEHCM (TCM) - just trans fluid change and filter change) 195,000 miles (not bad, eh?) 6.2 Liter L92 engine (Original Equipment, no serious work has ever been needed, never rebuilt - just well maintained) Vehicle is - from an interior perspective - 95% 'new'. I've spent the last couple of years restoring it. I've spent time and money on everything from new carpets to a new dashboard, HVAC assembly (in-dash), new seats, new seat motors, new windshield, new everything, for the most part I've done all this work myself. I've built up quite a tool collection and quite a bit of knowledge I work in the world of IT (Digital Experience Strategy for large and medium-sized companies) Being in this field of IT means I work all day in a world of total ambiguity and chaos where nothing is ever cut and dry and the options, ideas, and risks are endless...as are the personalities I deal with. Working on my vehicle - along with vehicle's owned by friends and family aware of my growing skill-set - provides me a level of calm and relaxation I can't find elsewhere
How This Story Originates:
In the last 4 to 6 months, I've noticed the transmission exhibiting a moderate 'clunk' when - IMO - it is shifting down from 3rd gear to 2nd gear, or during any low-load, low-RPM upshift from 2nd to 3rd gear. This happens only when there is low RPM / low 'Load' on the engine...followed by a quick increase in requested 'load'. For context, a situation wherein it commonly happens is during a slow-down at a stop light and my intentions are to turn right. I.e., 'right on red' with a slow, cautious crawl for safety. Assume no cars / traffic to negotiate (for simplicity). I'd say I'd be going at about 10 to 15 miles per hour...perhaps as much as 20 to 25 miles per hour...from a pre-braking speed of ~30 to 40 mph. I would take my foot off the accelerator about 100 to 150 feet before the red light and apply light braking. Once I'm in a position to begin my right turn safely, I would take my foot from the brake and apply ~30% to 50% throttle on the accelerator. At this point wherein I engage the throttle, it seems as if the transmission doesn't know which gear to be in. While it only takes about a second, it eventually chooses 2nd gear but in the process it makes a noticeable 'clunk'. To mitigate this 'clunk' I usually try to feather the throttle up a little bit before I'm about to release the brake (i.e., 2 - footed driving). Slowly getting the RPM's up above 1,000 before starting my right turn and releasing the brake seems to negate the clunk.
I've also noticed this clunk never really occurs until the transmission fluid temperature reaches about 110 (or above) Fahrenheit ( + /- 10 degrees).
All other gear shifts in all other situations are rather comfortable and exhibit no observable issues.
The transmission (nor the engine) never produces any DTC codes. Using a capable scan tool to reset the Trans Adapts and manually doing the Garage Shift procedure doesn't result in a 'fix'. Neither has anything else I've tried. I have not - to this day - ever tried doing a "Service Fast Learn". This is a procedure only incorporated into a few of the highly expensive scan tools such as the OE Tech2 and the Snap-On. My Autel Maxisys Elite definitely doesn't have this special function. One of these day's I'll have this procedure done by the Dealer or someone with a capable tool.
Last weekend, I decided to install a Sonnax Zip Kit for the 6L80. My thought process was that the temperature increase of the trans fluid was a key indicator and gave me good direction. I was thinking pressure was being lost when the internal components of the valve body heated up to a certain point and expanded ever-so-slightly...we're talking a thousandth or so of a millimeter in various places throughout the valve body veins / assembly...but enough where some trans fluid pressure was being lost in key areas and causing the resulting clunk. Because the valves themselves were a different metal (and some of them a type of polymer / plastic) and probably not expanding like the valve body casing, I figured this was a good enough hypothesis to start working against.
The Troubles Begin....
To make a long story shorter for you TLDR-er's, the Zip Kit is now installed and the shifting concerns seem alleviated. I'll give it another couple weeks to make a full conclusion, however. But the big story I wanted to share was about a mistake I made during the installation of the Zip Kit...but I imagine it could happen during any valve body refurbishment, upgrade, or maintenance. It has nothing to do with the Zip Kit itself. The Zip Kit was well manufactured and has fantastic instructions...with pictures too! The Zip Kit installation - plus a desire to inspect and clean all valves - simply gave me the opportunity to make the massive screw-up which occurred. So to help out fellow techs or DIY'ers who may experience this in the future, I have attached a summary pictorial explaining what I did and what it caused...along with the now-obvious solution.
Initial Start-up and Test Post-Cleaning, Assembly, Refurbishment - aka, "The Crucible":
What should have taken just about 3 hours to complete ended up taking 4 days. After putting everything back together the first time, I started the vehicle. I left it in Park for about five minutes. No unusual noises, no "Check Engine" lights. Normal oil pressure, normal slow rise in trans fluid temperature. Normal idle RPM's. I shifted from Park to Reverse and back to Park - allowing about 3 seconds between each move. This was an effort to flush air out of the veins/pump which may have accumulated during the overnight hours (I started this job in the evening but didn't re-install the valve body and other components until the next morning.) I then shifted from Park to Drive. I expected - as one usually does - to feel the torque and the car's desire to move forward. But no, there was no forward engagement whatsoever. I then shifted back to Park and let it sit for a minute. I shifted to Reverse - no reverse engagement. I left it in Reverse for 5 to 10 seconds thinking it will engage once the 'air is pushed out from the pump and valve body veins'...and that's when the Check Engine light came on. Silly me. I put it back in Park. I figured, let's try this again...maybe it was a solar flare or perhaps CNN is talking about Mueller again... Nope - same bad result - no forward, no reverse, not even the sound of it trying to engage. From Drive I was moving the shift lever back towards Park...and during that time I stopped briefly at Neutral. A faint squeal noise was observed from the transmission. Knowing that a squeal noise coming from a transmission is not SKOOKUM (h/t Ave on YouTube - one of my all-time favorites), I left it in Park and shut the engine off.
Exhausted, bewildered, and full of self-doubt, I removed the valve body and TEHCM two more times. For anyone familiar with accessing the transmission valve body on a 2007 - 2013 Yukon (and perhaps 2014 and beyond), you know it's not easy. Each time, the catalytic converters need to be moved / dropped. This means the O2 sensors need to be removed, the front drive shaft needs to be undone and moved off to the side a bit, the front right wheel and wheel well cover need to be removed, etc. etc. ....in addition to draining the trans fluid oil and making a mess of your garage floor and yourself. I did this without a lift...only a jack and jack stands...making me ache and strain in ways I haven't felt in years. Note to DIY's...it takes the catalytic converters a bit more time than you think in order to cool down to a manageable level...ask me how I know.
Each time I went over the instructions for the Zip Kit step-by-step to make sure I put the pieces where they were supposed to go. Each time I questioned most everything about how I put things back together - were the seals matching up correctly? Were the electronics / wires completely connected? Were there any green fuzzies on the main connector going from the outside of the trans and into the transmission case? Were there any cut or broken wires I didn't notice or failed to inspect? Each time I examined every piece that I had touched and questioned everything!...or so I thought. The struggle was REAL! Approximately 8 liters of new Dexron VI ATF - along with both hands, the right side of my jaw, and my lower back - were abused in the process of this event.
In short, during the re-assembly of valves which I had removed for cleaning, I put two of them in backwards. When they were first re-installed, they seemed to fit and it appeared how I re-installed them was exactly how I took them out. But I was incredibly wrong on both points. It wasn't until I noticed the ATSG manual's depiction of the valve body assembly diagrams - and comparing them to how I had re-installed my valves - that I finally realized the reasons for DTC's p0777 and p0700 suddenly appearing.
For SEO, (but explained in the pictorial), I'll simply say that DTC p0777 is "Clutch Pressure Control (CPC) Solenoid 2, Stuck ON" and was the only result post-assembly and start-up. However in the end there was nothing wrong with solenoid 2 whatsoever. The TCM/ECU only threw that code because the situation matched the DTC p0777 trigger conditions. At that point I was really close to spending ~ $600 bucks on a new TEHCM...and that's when I noticed I had installed Clutch Select Valve 2 and Clutch Select Valve 3 backwards. THANK THE GOOD PEOPLE AT ATSG WHO MAKE GOOD TRANSMISSION MANUALS..SPECIFICALLY THE DIAGRAMS (if only they were in color, btw.) Now getting people to read carefully...a different story , of course.
I couldn't find too much on DTC P0777, so I suppose it's rare. But if you ever come across this DTC or other "solenoid stuck", "solenoid failed" types of codes - and especially if you've just completed a refurbishing / cleaning / Zip-Kit installation on your valve body - take triple notice of how you reassembled and re-installed those valves....ALL OF THEM!
Thanks for your time,
I am trying to find out what exactly my max tow rating is. First off, I have believed since I owned the truck that it had 3.73 gears. I requested the build sheet from GM and turns out I actually have 3.08 gears (RPO code GU4). I also thought I had the heavy duty tow package (RPO code Z85), but the build sheet says I have the "Trailering Package (Special)(Reese Type Hitch)" which is RPO code Z82. The sticker on the drivers side says the weight of cargo and occupants should not exceed 1577 lbs. So, 7700lbs GVWR - 1577lbs cargo capacity = 6,123lbs curb weight?
According to the below site, the max towing capacity is 11,200lbs with 3.73 and max trailer tow, which is what I thought I had. With 3.08 gears and no max tow package, it is only 6,600 lbs, which is a huge difference keeping safety in mind. The guide does mention Z82 as the heavy duty package, but does not explicitly call Z82 the "Max Trailering Package". What i think is happening here is the Z82 is the Max Trailering Package on a Z71.
https://my.chevrolet.com/content/dam/gmownercenter/gmna/dynamic/manuals/2014/chevrolet/Multiple Model PDFs/MY14 Trailering Guide_1113.13 - Equinox.pdf
So, now that I am unsure of what exactly my tow rating is, I just want to confirm I know the correct limits of my truck.
Truck: 2014 Silverado Crew Cab, LTZ Z71, Short Box
RPO codes that may help:
GU4: Axle, Rear, 3.08 Ratio
JD9: Brake Vac Power, 17" Disc/Disc, W/VSES, 7700 LBS
JL1: Control, Integrated Trailer Brake
KC4: Cooling System, Engine Oil
KNP: Cooling System, Transmission, Heavy Duty
L83: Engine Gas, 8 CYL, 5.3L, SIDI VVT, AFM, E85 MAX, ALUM, GM
MYC: Transmission Auto 6SPD, HMD, 6L-80
Z82: Trailering Package (Special)(Reese Type Hitch)
Again, I have the full build sheet so just let me know if that would help you guys help me
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.
Recently Browsing 0 members
No registered users viewing this page.
Most OnlineNewest Member
Who's Online 70 Members, 0 Anonymous, 1,610 Guests (See full list)
- Rick Harwood
- Balraj Sohal
- Miguel Olea
- Turd Ferguson
- Kole Zimmer
- Dustin Reed
- 14 Silvy
- Old wrench 🛠
- Jared Hoefsmit