Absolutely it’s always great to post these finds for the next person. This rattle almost made want to trade this in lol. Thats how bad it was. Other then my 8speed reverse clunk hoping warranty fixes it. I would say having a permanent rattle that cannot he found is worse. I took apart almost everything and zip tied this and taped that etc. went underneath the dash taped a lot of wires etcc…. I even thought it was shocks. Rattles are evil and serve no purpose.
Took the truck in last week to continue the diagnoses on the reverse clunk. But the transmission techs were both out due to Covid. Service adviser said they should be back this week. Then I’ll go back. So far this dealer has been good going to let them check if they can’t then I’ll try another dealer. I have 2k miles left in my power train warranty. But the service adviser said he noted my issues in case I go over my warranty.
Been chasing a very pronounced dash rattle directly behind the cluster for months. Almost Removed the entire dash and no luck. The interweb didn’t help much, never seen this before. just earlier I removed the windshield wipers and plastic cover and found a really loose bolt. Under the wiper motor. Not tight at all. Had to use the impact because it kept spinning I assume there’s a nut on the other side. Now it’s tight. My cabin is now RATTLE FREE. 2019 CC z71 58k miles.
So anybody have this jolt/clunk/bang with a small delay going into reverse? Along with a rattle on their drivetrain near the transfer case.. . Or does your 8l90 shift like butter going into reverse??? With no noise from underneath. Is it supposed to?…. I did try it in 4lo and 4hi and the clunk is actually a lot less going into reverse not sure how. if you had this issue what was the fix? It happens every single time I go into reverse unless the RPMS are high on a cold start the drivetrain feels tight. Then at idle it gets sloppy again. my in laws 6l80 shifts in to reverse like butter you don’t feel any noise or delay or movement in the drivetrain. Taking it back for the dealer I have 2k miles left on my warranty. Last ditch effort if they say it’s operating as designed or cannot fix it otherwise. Might trade this in for a custom trail boss with the 6 speed idk…. unfortunately don’t want to risk this failing after warranty… things like this make me want a more base trim for the long run… the less tech and less gears the less complexity.
Got the dealer to take a look. And they said they also saw a shutter due to the fluid and also confirmed my reverse clunk issue. According to their computer graph they can see the shutter. They did the Mobil 1 blue label flush. It did not fix the reverse clunk/bang into gear.
Not to thread Jack. But speaking of the new 158f thermostat since so far it’s only out for the 6l80…for those who might want to use a factory method of lowering the 8l90 temperature I decided to buy one from the dealer about 2 weeks ago thinking I can use it in my 8l90 but the housing is different so I just opened it swapped the “pill” they are identical other then the 135F stamp And 180F stamp on the 8l90’s…. I simply reused my 8l90 thermostat housing and happy to report it works as intended I drove about 6 hours total today towing a light car on a trailer and the highest I saw was 165F in town. And highway was 145 ishh. without towing after fully warmed up it’ll hover between 140 and 160 id you drive like a maniac it’ll go up to 169 at the max. And that’s trying. With 75 degree SoCal weather. Will never go back 190+ temperatures on any GM trannys. That Heat kills them by 150k or less miles IMO and all the data I’ve read etc.
Thanks for the reply. Yup so we seem to have the same issue. Expect yours doesn’t do it anymore when you drive it a few miles at least. I think yours sounds like the “delayed engagement” Because that issues explains that it only does it on the initial reverse then goes away…. And comes back if left overnight etc…probably a good idea to leave it at the dealer over night so they can see the issue on a cold start. In my case The only time mine doesn’t clunk/slam is on a cold start when the RPMS are over 500 if I shift to reverse quickly it won’t do it at all. everything is quite. Once the normal idle of 500 comes in it’ll clunk 24/7 all day everyday into reverse smh. And yes when it’s slams it feels like something drops hard down underneath you… one solid loud bang. it can’t be good but I don’t get why some 8l90 are smooth as hell. Must be a software issue. Or idk my transfer case because all that moves and shakes hard on the clunk… it shifts just fine other then that. Going to try and get it to the dealer before warranty is gone. I’m at 55k
Tried to upload video but to big I guess. I was wondering if it’s normal for 2019+ Silverado 8l90’s to have a clunk/bang going in to reverse from park and also from any gear to reverse for that matter I saw the drive shaft that connects to the transfer case when testing and it moves shakes violently when I go reverse only. Truck has almost 60k miles. And has had the atf changed. Always thought this was normal. Until my inlaw said wth is wrong with your truck. my in laws 6 speed older Escalade doesn’t do this all at always shift like butter going into reverse. could it be a characteristic of the 8l90’s? I attached a photo of the shaft that shakes like crazy and the transfer case. Only when I go into reverse. Has done this since brand new. Just always thought it was normal. Maybe the transfer case is loose or idk. Worried this tranny can go after warranty. If this isn’t normal and the dealer says it’s normal might potentially trade in. Does your 8l90 have a heavy loud bang going into reverse? Cold or warm
I did the drain and fill on a hot tranny. Yup. I must have overfilled it on the previous services thousands of miles ago but didn’t realize it. So I guess I was 2 quarts over filled this long. But never had any issues luckily
Just did another drain and fill on my 19 cc z71 8l90 last night. Measured what came out and refilled…. This morning I decided to do the fluid check procedure. Between 95F tranny temp and 113F on level ground I opened the overflow plug at around 104F and let drain what comes out to make sure level is correct etc. 2 quarts drained back out and then it came to a small drip. Been driving like this for the last at least 20k miles since I did drain and fills a couple times already before. trucks never shifted bad or anything. Found this interesting though apparently being overfilled 2 quarts. My thermostat is flipped btw not sure if that changes anything on the procedure.
Results are in STL010 average open highwaytemp is 140 Heavy city use is up to 197f stays at around 197 if I idle for an extended period flipped stock thermostat average open highway is 150f Heavy city use is up to 176f Temp goes down to 167 if I idle extended periods. same constant average load of about 600 pounds of loaded pallets with batteries in my bed with same routes and stops … All day for about 8 hours of total engine hours. 50/50 city highway. Average California 90 degree weather. both tests were done in literally the same circumstances very consistent 2019 Silverado CC Z71 8l90 with 51k miles transmission has had 3 drain and fills of about 6 quarts each time since purchased new. With blue label Mobil 1 atf. Filter was changed out 1 time at around 20k miles Front and rear diff are running Amsoil 75w90 since 50k miles. engine has had Mobil 1 0w30 since new no issues. and recently I’m trying out 5w30 Penzoil ultra. Always changed oil at 5k miles since new. No DFM disabled lol running it stock.
I did the sure cool STL010 on my 19 5.3 8 speed and my averages for the last 2 weeks in 80 degree socal weather has been 140f on highway drives and in constant city driving it reaches up to 197f but I do drive my truck all day for about 6 hours daily. so out of curiosity I removed the sure cool and did the pill “flip” on the OG thermostat to see if the results are the same in city driving or lower. my question to anybody that might know is to check the fluid level with the pill being “flipped” is it still the same procedure and temperature range? For the 8l90’s considering that now theirs a constant immediate flow also it would be nice if GM released a new T stat at 158f for the 8 speed and called it a day. Their must be a reason why the 6 speed got it lowered.
if your talking about the 2 bolts that hold the bottom of the strut down. I think you can thread them from top to bottom then the clearance issue would be non existent. Other then that I’ve tried the rough country 2 inch level and it was fine for my 19 CC LT Z71 bolts facing up and all.
I had the EXACT same issue develop with my 19 LT Z71 around 20k miles I now have almost 50k miles and it never did it again. After I took it in and described what you said… they checked and said it was a “software anamoly” and updated the transmission I called it the the 2-1 transmission jerk only happened when coming to a stop. After they fixed it I drained and filled my tranny with the new Mobil 1 blue label ATF and mew filter from the dealer. For good measure. Because of possibility that that is was filled with the old specd ATF fluid since mine was one of the first 19’s produced. This 8 speed has been great since then.
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