1. Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

4L80E Overdrive Issues HELP!!!

Discussion in 'All Other Transmissions' started by MTPKTS, Oct 30, 2017.

  1. MTPKTS

    MTPKTS New Member

    4
    0
    Oct 30, 2017
    Knoxville, TN
    Hello All!!! New time subscriber but a long time reader. I have been all over this site trying to find some direction with my transmission problem but I feel like I am striking out. Any Help would be appreciated.
    1997 GMC 2500 4 WD 6.5 TD 4L80E.
    The truck drives fine when cold and shifts through all gears as it should Once the vehicle warms up (15-20) and under normal driving all is fine until I attempt to go up a slight grade or stomp on the accelerator and the truck down shifts from OD to 3, usually around 50 mph. When it down shifts is slips and revs real high, like I pushed the clutch in. If I manual shift the trans into 3 it drives without missing a beat. I have no warning lights on and this started out of the blue with no gradual signs. Any help with this is greatly appreciated.
     
  2. Jaryd

    Jaryd Oh the sound a 6.5 makes

    648
    792
    Nov 27, 2016
    Hodges, SC
    Have you checked the fluid lately. If so does it look dark or smell burnt
     
  3. MTPKTS

    MTPKTS New Member

    4
    0
    Oct 30, 2017
    Knoxville, TN
    Both. Dark and smells a little burnt.
     
  4. smokymtn65

    smokymtn65 Well-Known Member

    283
    388
    Aug 21, 2015
    East TN
    Welcome neighbor. Best shop in town... Steve Walker at Marshall's Trans he wont charge you for a test drive and is straight up!
     
    MrMarty51 and Jaryd like this.
  5. WarWagon

    WarWagon Well it hits on 7 of 8...

    8,163
    2,534
    Nov 15, 2009
    AZ
    Trans codes are NOT EPA Check "engine" codes so they don't turn on the Service Engine Soon light. Pull codes and see if that gives you a direction.
     
    Jaryd and MrMarty51 like this.
  6. MTPKTS

    MTPKTS New Member

    4
    0
    Oct 30, 2017
    Knoxville, TN
    Thanks neighbor I'll try and get in there this week.
     
  7. MTPKTS

    MTPKTS New Member

    4
    0
    Oct 30, 2017
    Knoxville, TN
    Right on! Thanks Do you get the codes the same way you would get the SES codes? With a paper clip?
     
  8. WarWagon

    WarWagon Well it hits on 7 of 8...

    8,163
    2,534
    Nov 15, 2009
    AZ
    OBD1 1995 and older uses a paperclip. OBDII requires a scanner or other trick I don't recall offhand.
     
  9. THEFERMANATOR

    THEFERMANATOR FRANKENBURBAN Staff Member Lead Moderator

    8,978
    2,306
    May 9, 2008
    ZEPHYRHILLS FL
    You have to have a code reader, and you need to pull the codes. Sounds to me like your losing fluid pressure. When the trans is cold, the fluid is thick, but when hot it thins. Thinner fluid is harder to build pressure, and if theres a leak, it will show when the fluid is thin.

    Have you serviced this transmission or had it serviced since 06? If so, do you know what fluid was used? If dexron 6 was used, it has taken the seals out in several transmissions as it is a very dry low viscosity fluid. GM superceded dexron 3 to dexron 6 because they changed on the assembly line when dex 3's patent ran out. Dex vi has killed many transmissions, but it normally takes 6 months to ayear to happen.
     
    Last edited: Nov 1, 2017
    Husker6.5 and MrMarty51 like this.

Share This Page