Jump to content

2014 - 2018 5.3 6 speed downshift jerks

nluchau
 Share

Recommended Posts

  • Replies 98
  • Created
  • Last Reply

Top Posters In This Topic

Popular Days

Top Posters In This Topic

Popular Days

Popular Posts

nluchau
nluchau

My 2016 5.3 6 speed has me very frustrated to say the least.  I know I've brought this up before but I need to again. I am still getting the jerk downshifts when coasting/slowing to a stop.  I don't h

nluchau
nluchau

No problem!  Seems to be a widespread issue with no resolution.  

btj_z71
btj_z71

Go for a custom tune like black bear.  They tune the ECM and TCM.  Will update the transmission tables too, makes a huge difference.   Another option is to check all the fluids in your drive

Posted Images

Racindave Enthusiast

Racindave

Posted
Posted

If I drive my truck like a mature person it’s super smooth taking off and stopping (especially if I run 89 octane). If I drive it  like I stole it it gets all herky herky for a bit. Once I drive normal again it clears up. I’m just chalking it up to the transmission trying to save me gas and figuring out how I want it to drive.  Honestly, I can live with it.  Love everything else about it. 

  • Like 1
  • 2 weeks later...
Bob2C Enthusiast

Bob2C

Posted
Posted

Installed Gibson exhaust and the harsh downshifting is gone.


Sent from my iPhone using Tapatalk

dieselfan1 Senior Enthusiast

dieselfan1

Posted
Posted
9 hours ago, Bob2C said:

Installed Gibson exhaust and the harsh downshifting is gone.


Sent from my iPhone using Tapatalk

I highly doubt the exhaust had anything to do with it.

Bob2C Enthusiast

Bob2C

Posted
Posted
I highly doubt the exhaust had anything to do with it.


Don’t know what else it can be. Been like that since new and now have 12k miles on it. The only thing different is the exhaust. Just weird
mmmikkke Senior Enthusiast

mmmikkke

Posted
Posted
17 hours ago, Bob2C said:

 


Don’t know what else it can be. Been like that since new and now have 12k miles on it. The only thing different is the exhaust. Just weird

 

It's conceivable that the TCM has a coding error that adapts to "idle" throttle position changes caused by having the a/c on (higher throttle position needed to idle at 600 rpm) or by having a less restrictive exhaust (lower throttle position needed to idle at 600 rpm).  Perhaps there exists a coding error that mishandles the default idle throttle position and properly handles the other 2 throttle positions I described above.

 

I noticed on my truck that if I brake to a stop (using my left foot) while having the throttle only a tiny bit open, the 3-2 and 2-1 downshifts are much stiffer.  So this could be a 3rd idle position.

 

Has any reader of this thread actually gotten revised/updated shift tables uploaded into their TCM by the dealer under warranty?

 

I challenge GM engineering to release a technical document describing the design objectives and features of this advanced transmission that learns how I drive.  Does it compensate for how I drive?  Does it shift earlier or later because it has learned I am a lead foot or slow poke?  How long does the learned behavior persist?  Or once it learns I am a lead foot, does it relearn only with a battery cable disconnect? 

 

Or do we all have to get hptuners in order to fix these issues?

  • Like 1
Bob2C Enthusiast

Bob2C

Posted
Posted

The thing I did do but failed to mention was disconnect the battery while I installed the exhaust as stated in the installation procedure.


Sent from my iPhone using Tapatalk

dieselfan1 Senior Enthusiast

dieselfan1

Posted
Posted
39 minutes ago, Bob2C said:

The thing I did do but failed to mention was disconnect the battery while I installed the exhaust as stated in the installation procedure.


Sent from my iPhone using Tapatalk

That's odd they want you to disconnect the battery to put exhaust on it.

I don't remember that when I installed the Borla. Actually I didn't even read the directions.

  • Haha 1
Bob2C Enthusiast

Bob2C

Posted
Posted
That's odd they want you to disconnect the battery to put exhaust on it.
I don't remember that when I installed the Borla. Actually I didn't even read the directions.


I found it odd too but they said it had something to do with the computer learning the correct pressure so it didn’t throw a code. Maybe it was overkill.


Sent from my iPhone using Tapatalk
  • 4 weeks later...
nluchau Enthusiast

nluchau

Posted
  • Author
Posted

So about 3500 miles ago GM put in a reman transmission as a customer satisfaction for me.  I still feel the firm downshifts but not as bad.  The one thing I notice now ever since the 2nd transmission is the upshifting seems a bit firm.  If its cold and I increase throttle and hit 33mph it abruptly upshifts into 5th gear.  1st - 4th seem fine just when it hits 5 it feels like it drops into 5 vs a slow ease into 5.  I'm not heavy on the throttle either.  I talked to the service manager right when I first noticed it, a few days after getting it back from repair.  He said to give it 3-4k miles and let him know if it still happens as the transmission has a learning curve.  One thing I've also noticed is the trans fluid (when checked cold) is way up on the dip stick overfilled.  

 

My question is what can the dealer do now with this abrupt upshift into 5. Would a tap reset, or any other reset possibly correct this? 

 

Thanks for any info

  • 3 weeks later...
mmmikkke Senior Enthusiast

mmmikkke

Posted
Posted

I'd have the dealer correct the fluid level free of charge since they're obligated to follow GM instructions when doing repairs.  I can't imagine a TSB instructing the tech to overfill the transmission.  If they claim the dipstick is wrong then have them get you the correct dipstick.  SMH on your dealership.

mmmikkke Senior Enthusiast

mmmikkke

Posted
Posted
On 9/4/2019 at 11:15 AM, nluchau said:

So about 3500 miles ago GM put in a reman transmission as a customer satisfaction for me.  I still feel the firm downshifts but not as bad.  The one thing I notice now ever since the 2nd transmission is the upshifting seems a bit firm.  If its cold and I increase throttle and hit 33mph it abruptly upshifts into 5th gear.  1st - 4th seem fine just when it hits 5 it feels like it drops into 5 vs a slow ease into 5... Thanks for any info

@nluchau, are you feeling the tcc (torque converter clutch) lockup?  At light throttle, it can occur (is permitted by a data table in the TCM) any time after 2nd gear is engaged, so your 2-3 shift could happen simultaneous with the tcc lockup.  At 1/8 throttle,  with my truck, tcc lockup occurs after the 1-2 shift.  At 1/4 throttle,  with my truck, tcc lockup occurs after the 2-3 shift.  This suggests the TCM has some leeway on its deciding when is a good time to lock.  With my truck, the tcc lockup is much slower than the gear-to-gear shifts.  The slow lockup deserves the "ease into gear" characterization, so I was wondering if you have the tcc lockup event properly categorized given that you didn't mention it.

 

With a cold transmission, below 32F, the TCM does not lock the tcc at any speed, until the transmission temperature gets above 32F.  This can give people in colder climates additional diagnostic info...

 

Your thoughts?

  • 4 weeks later...
nluchau Enthusiast

nluchau

Posted
  • Author
Posted
On 9/27/2019 at 10:27 AM, mmmikkke said:

@nluchau, are you feeling the tcc (torque converter clutch) lockup?  At light throttle, it can occur (is permitted by a data table in the TCM) any time after 2nd gear is engaged, so your 2-3 shift could happen simultaneous with the tcc lockup.  At 1/8 throttle,  with my truck, tcc lockup occurs after the 1-2 shift.  At 1/4 throttle,  with my truck, tcc lockup occurs after the 2-3 shift.  This suggests the TCM has some leeway on its deciding when is a good time to lock.  With my truck, the tcc lockup is much slower than the gear-to-gear shifts.  The slow lockup deserves the "ease into gear" characterization, so I was wondering if you have the tcc lockup event properly categorized given that you didn't mention it.

 

With a cold transmission, below 32F, the TCM does not lock the tcc at any speed, until the transmission temperature gets above 32F.  This can give people in colder climates additional diagnostic info...

 

Your thoughts?

Mike - Sorry for not seeing this until now.  I am certain I feel it locking up while accelerating.  Does it feel like some torque is being added somewhat?  I wish I could drive it once without it locking just to feel what the downshifts would be like.  I'm pretty sure what I am feeling is the TCC unlocking and locking again during downshifts when coasting but its rather harsh and jerky when it occurs.  In town driving sucks to say the least.  Interstate travel is great of course since it stays in 6th.  Wish I knew if this could be resolved or not.  It appears not though...

mmmikkke Senior Enthusiast

mmmikkke

Posted
Posted

My truck's tcc lockup by itself is not harsh or jerky.  For my 2016 Silverado 4.3L V6, harsh or jerky describes the 3-2 and 2-1 downshifts as I come to a very gradual stop and the tcc has not yet unlocked.  At zero throttle, decelerating to a gradual stop, my truck's tcc seems programmed to unlock after the 2-1 downshift, just in time to NOT lug the engine before shedding those final 2 or 3 mph.  In other words, under the described conditions, tcc unlocks at the "last minute" so that engine RPM stays above or at 600 (idle) as the truck slows to 3, 2, 1, and finally 0 mph.  I'm considering buying an hp tuner at hptuners.com just so I can play with the tcc minimum speed (minimum unlock speed while decelerating).  It seems if I could raise tcc min speed to maybe 10 mph. then the 3-2 and 2-1 downshifts would occur while the tcc is unlocked, and so the torque converter's fluid coupling would absorb the 3-2 and 2-1 downshift harshness and all would be good.

  • Like 1

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing

  • Latest Articles

  • Posts

    • newdude
      Transmission Woes :-(

      By newdude · Posted

      You need a better code reader/scanner.  You are missing codes.  Did the dealer give you a copy of the SAVI scan from that visit?     If the fluid hasn't been changed, change it.  Shudder will likely go away.  
    • newdude
      Can anyone decode a VIN to determine if this truck has had emissions issues or a recall?

      By newdude · Posted

      TLDR to my other post...   Hard. Pass.  Too many what ifs.     Are you set on a 3.0 Duramax?  Have you considered anything not GM just in case?  If you don't have to have a pickup, lots of other options for $27,000 out there.   
    • newdude
      Can anyone decode a VIN to determine if this truck has had emissions issues or a recall?

      By newdude · Posted

      I see some red flags.   - No mention in the Carfax if the oil pump belt was changed.  LM2s had a 150,000mi service interval, and its got 164,245mi on it.  So right out the gate it needs about $3000-3500 for that to be done before driving it another 150,000mi.  Belt is at the rear of the engine.     - If something happens to the transmission valve body, the special coverage is expired by mileage.  That will likely be an out of pocket expense, with zero or near zero GM participation if something happened even though its in by time.   - 2020 LM2s seem to need timing chains after 80,000mi at some point.  They fixed this end of 2020/starting 2021 model year engines.  They will usually set a P0016 I think?  There is another $8000-10,000 if it needs a chain.  The main chain is at the back, secondary at the front so the pump belt would be done at the same time if it needed chains.     - Long oil change intervals.  7,000-8,000mi on average, probably close to 0% or perhaps to or beyond 0% on the OLM.  Lots of them not at the dealer which makes me wonder how much of the oil ran through that truck was the proper Dexos D rated 0w20 oil and not just gas engine 0w20, which is not the same at all.     - Long fuel filter changes, again likely taking the fuel filter life to 0% or more.  First one went 28,603, second was done 43,094 miles later at 71,697, from there another 46,452mi to 118,149mi, and then the most recent one 37,026mi later at 155,175mi.  So counting its original fuel filter, its had only 4 fuel filters on it.  No bueno IMO.         Good news?    - It has had only two warranty trips to the dealer.  The first free service (end of December 2020 on the Carfax), and the transmission reprogram recall (end of August 2025 on the Carfax).     - Truck did a LOT of moving, so that might explain the lack of emissions related repairs like bad NOX sensors, bad exhaust temp sensors, bad glow plugs, etc.         The "emissions system checked" could just be how something was flagged for Carfax.  GM dealers have to do SAVI reports for warranty repair orders so they scan the truck.  So its possible that is there for that?  
    • cherryred21duramax
      Can anyone decode a VIN to determine if this truck has had emissions issues or a recall?

      By cherryred21duramax · Posted

      Thank you, @Z45!   NOTE - No all repair shop/Dealers reports to Carfax   That is my main concern.  The CARFAX looks way too clean for a 6 year old anything with 164,245 miles.  Even something known for reliability (like many Toyotas) typically has a lot more replaced, like a Nav screen, interior trim, shock/strut, or brake pads.  And surely the last set of tires (installed at ~58k miles) would be bald unless those were all highway miles.   I'm tempted to pay a local dealer to look up the VIN, but am not sure if that will be worthwhile.  Last time I did this, it was 100% useless, and I felt scammed - they noted the bumper was replaced years ago and that's it.  A 5-year old could spot the accident damage, even though nothing was on the CARFAX.   After giving the dealer a call, the truck may have a hard shift, but they have to verify with their mechanic if that's even a concern.  And I've test driven about a dozen of these now, many near Chicago, and half the trucks shift hard/odd at all throttle positions.  The ones with aftermarket lifts/larger tires shift terrible, and 3 stock trucks shifted so violently I thought the transmission valve body was going out.   At this point I'm conflicted, as I need a vehicle, and am coming up short locally.  Northern trucks in this price range tend to have either multiple owners, a lot of mods (lifts/oversized tires without re-gearing), and are generally in rougher shape.   If this truck showed up in your neighborhood for $27k and you had to purchase it sight-unseen, with the possibility of needing a 10L80 rebuild, torque converter, or rear end - would you do it?  I'm convinced most of the 10L80 trucks I test drove are broken, they can't all shift so bad, with massive flares/slipping/lurching and mis-matched downshifts like a teen driver learning stick.
    • Griffin Donovan
      2027 GMC Sierra Spot Shots + Undisguised Interior (BIG Changes!)

      By Griffin Donovan · Posted

      From the spy shots, the front end does look like it's borrowing some styling cues from the Canyon. I'm more interested in the powertrain news than the screens though. If the 3.0 diesel survives into the next generation, that alone will keep a lot of current owners interested.  

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...