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Flushing 8L90 8 speed transmission

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MRP Enthusiast

MRP

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While I was searching for info on flushing and changing transmission oil on the 8 speed (going from Dexron HP to Mobil 1 LV ATF HP), I found this GM technical service bulletin that is specific to the flushing and changing fluid on the 8 speed 8L90 transmission in various applications.  Although one would not have the special tools/equipment that GM has, it gives you a solid guideline on the procedure to follow as well as torque specs.  Hope this helps the DIY guys out there.

8L90 flushing proceedure.pdf

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Lee Roy Enthusiast

Lee Roy

Posted
Posted

Had my 2019 flushed by the dealer and the shifts are harsher than before the flush. It seemed better for the first 4-500 miles than got worse.

Z45 Senior Enthusiast

Z45

Posted
Posted

Be advised the 6sp, 8sp and 10sp each use a different ATF. Using the wrong atf can affect performance.

 

Automatic Transmission (6-Speed Transmission) DEXRON-VI Automatic Transmission Fluid.
Automatic Transmission (8-Speed Transmission) DEXRON-HP Automatic Transmission Fluid.
Automatic Transmission (10-Speed Transmission) DEXRON ULV Automatic Transmission Fluid.

ULV stands for Ultra Low Viscosity.

  • 3 weeks later...
mfbearded Enthusiast

mfbearded

Posted
Posted
On 7/5/2021 at 2:19 PM, Lee Roy said:

Had my 2019 flushed by the dealer and the shifts are harsher than before the flush. It seemed better for the first 4-500 miles than got worse.

how many miles beofre the flush ? im at 47000, dealer told me i needed it last oil change...part of the 45000 maintenance package 

Adamace1 Enthusiast

Adamace1

Posted
Posted
38 minutes ago, mfbearded said:

how many miles beofre the flush ? im at 47000, dealer told me i needed it last oil change...part of the 45000 maintenance package 

I think its recommended at 45k in severe condition by gm. So if you tow alot, idle alot, off road, live/ drive in mountains alot, alot of short trips ect ect. It's almost 100k if it's a highway queen. 

Gangly Senior Enthusiast

Gangly

Posted
Posted (edited)

According to the recommended maintenance interval in the back of the owners manual, for Severe Service the recommended interval is 45,000 miles for fluid and filter change.  I cant find an interval for non-severe service.

Edited by Gangly
diyer2 Senior Enthusiast

diyer2

Posted
Posted

I would do the 45 K, but that's me.

Gangly Senior Enthusiast

Gangly

Posted
Posted

Same here, I'll prolly do a transmission fluid change at 45k, but not a flush.

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