8 speed

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Thread: 8 speed

  1. #1
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    8 speed

    How is your 8 speed transmission, mine has issues that dealer cant fix

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  3. #2
    4.6 Liter Northstar V8 rockyspaw's Avatar
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    Re: 8 speed

    According to TSB (Technical Service Bulletin) 18-NA-355, the latest update addresses “torque converter clutch (TCC) shudder conditions on 8L45 and 8L90” eight-speed automatic transmissions, RPO codes M5N, M5T, M5U, and M5X. Affected vehicles include Chevrolet, GMC and Cadillac vehicles.

    As of July 8th, 2019, GM began using a new type of Mobil 1 automatic transmission fluid for the troublesome transmissions. Customers that complain of shuddering and harsh shifting characteristics in the 8-speed GM transmissions are recommended for a trans fluid flush. As of August 7th, GM dealers should also be flushing all potentially affected new vehicles on the lot.
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    6.2 Liter LS9 Supercharged V8 TruckMan's Avatar
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    Re: 8 speed

    Mine had the shudder and a torque converter replacement a while back. No problems since. Glad I have the 100k mile warranty. I'm at about 65k.
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  7. #4
    4.6 Liter Northstar V8
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    Re: 8 speed

    I have the 45 in the Colorado and through 5k miles so far no issues, every once in a while I can feel a bit of a jerk in the 2-1 downshift coming to a stop, but no shuddering issues.

    Regarding rockys post above, that's interesting, I presume that's for the full sizers. On the Colorado/Canyon forums, March '19 was stated to be the factory switchover date for the M1 tans fluid. I also read that dealers were supposed to flush any trucks in stock at that time. Now, my truck was a 1/19 build although I bought it in November. So I'm not sure which fluid it has. I'd like to believe the dealer followed GM's direction to flush it, but I never hold a lot of faith in dealers.
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