Now that we are getting “back on the field of play” let’s take a closer look at the 8L90 shift quality concerns. Shift concerns are just like playing the shift in a baseball game with that big left-handed power hitter that hits everything to the right side of the field. You know it’s going to happen, especially with the 8L series transmissions. Flares, bumps, and tie-ups are all common issues on Gen 1 units. Later-generation 8L applications have dramatically improved shift quality, so you’ll most likely face these issues with the early generation applications. So, let’s play ball!
Every year since the first 8L was introduced in 2015, we’ve talked about different types of shift concerns, but confusion with the processes that must be followed still exists. Time to suit up, hit the field, and clarify any points of confusion here on the field of play.
Starting at first base are the facts regarding 8L shifting. With 8L applications, the TCM must apply three clutches to make the unit operate for each gear. That means to make a gear change, the TCM must release a clutch and apply another clutch. Which clutches are released and applied depends on the gear the TCM wants to select.
The TCM deals with multiple clutches during a shift. The adaptive learning system must learn the “Applying Clutch” and the “Releasing Clutch” rate of apply. This complicates the adaptive learning systems job as compared to some other units. Shift quality is dependent on factors other than just the shift adapts.
The type of fluid used is one of those factors. Make sure you are using the correct generation of Dexron LV fluid. Make sure the clutch travel is correct for all clutches, as a travel issue may make it difficult or impossible for the adapts to make enough adjustments to eliminate the shift quality concern you are dealing with.
Stealing second base is easy when you have various calibrations that have been released to address shift concerns. Make sure you check and or update your TCM software. Is the PUN/TUN correct for your applications? If not, update the PUN/TUN.
The shift adapts system needs to be cleared, and then a fast learn needs to be performed to allow the system to “rough-in” the shift feel adjustments. This is a key point, so don’t get picked off trying to steal second. If you fail to clear the shift adapts, you won’t score; you’ll get picked off! Clear the adapts, then perform the fast learn.
Once the fast learn is complete, an extended test drive needs to be performed. The test drive includes multiple upshifts and downshifts at different throttle openings and speeds.
If any shift is still objectionable, perform an “individual clutch adaptive learn” based on the shift that is a problem. The transmission fluid temperature must be between 35° – 95°C (95° – 203°F) for the adapts to relearn.
Let’s take a look at the batting order. Select which clutch(es) need to be relearned individually (see above). Use your scan tool to access the individual clutch learn menu for each clutch (Figure 1).
C1 relearn: In the M Range, shift the transmission into 6th gear manually. Obtain an engine speed between 1000 and 1600 engine rpm. Maintain for a total of about 8 km (5 mi). In the D range, complete fifteen light throttle 6-7 upshifts at approximately 15% throttle to further learn the C1 clutch.
C2 relearn: In the M Range, shift the transmission into 8th gear manually. Obtain an engine speed between 1000 and 1750 rpm. Maintain for a total of about 8 km (5 mi). In the D range, perform ten normal 6-5 coast downshifts (zero/light brake) to learn the C2 Return Spring pressure.
C3 relearn: Complete fifteen light throttle 2-3 upshifts at approximately 15% throttle to learn the C3. Perform ten 8-7 coast downshifts (zero/light brake) to learn the C3 Return Spring. To enable the adaptive learn on 8-7 coast downs, a power 15% throttle through the upshift must be accomplished on 7-8 upshift before each downshift.
C4 relearn: In the M Range, shift the transmission into 7th gear manually. Obtain an engine speed between 1000 and 1750 rpm. Maintain for a total of about 8 km (5 mi). Perform ten 7-6 coast downshifts (zero/light brake) to learn the C4 Return Spring. This action enables torque converter clutch (TCC) to control the slip during a downshift versus the TCC to unlock fully. This naturally occurs on normal downshifts and disables adaptive learn. In the D range, complete fifteen light throttle 1-2 upshifts at approximately 15% throttle to learn the C4.
C5 relearn: In the M Range, shift the transmission into 3rd gear manually. Start a very slow acceleration, starting at about 1000 rpm. Maintain the slow acceleration until you reach about 2500 rpm. Once you reach 2500 rpm, slow back down to 1000 rpm and repeat the slow acceleration up to 2500 rpm (Repeat this ten times). In the D Range, complete fifteen light throttle 3-4 upshifts at approximately 15% throttle to learn the C5.
Power Down Shift Adapts:
With the vehicle in 8th gear, slowly apply pressure to the accelerator pedal until a downshift occurs. Repeat for each gear/shift (8, 7, 6, 5, 4, 3 and 2).
Garage Shift Adapts, N to D and N to R:
This process should be performed after the C3, and C5 clutches have fully learned. With the vehicle stopped, apply the brake and move the shifter from Neutral to Drive. Release the brake, allowing the vehicle to roll 5-10 feet, then stop. With the vehicle stopped, move the shifter from Neutral to Reverse. Release the brake once in gear allowing the vehicle to roll 5-10 feet.
Those are the keys to victory. Repeat the processes as many times as necessary until desired shift quality is achieved. Keep in mind, it might take extra innings to get the job done, but there are no shortcuts on the road to victory! The 2018-2021 applications will show the clutch learn status via scan data for all the clutches, so you know the learn was complete.
You need to have a game plan going into the job. Execute that game plan and remember, repeat the processes as many times as necessary to get that shift quality you’re looking for…
And that’s the Game!
