Flushing 8L90 8 speed transmission

[MRP]

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

[Gangly]

Great info, thanks for posting this up for everybody!

[zhmorrow]

Helloc

 

ant chance you have the service bulletin for the 10spd? Looking to flush my 6.2/10

[Lee Roy]

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]

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.

[mfbearded]

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]

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]

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 July 27, 2021 by Gangly

[diyer2]

I would do the 45 K, but that's me.

[Gangly]

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