- Author: Wayne Colonna, Technical Editor
- Subject: A6MF2H
- Issue: Ring Shift
Not often do we get the opportunity to work with a tech that is having issues with a transmission in a hybrid vehicle. Not too long ago, Gerald Campbell had the chance to do just that with Carlos Costa from Transmission Technology. He had a 2012 Kia Optima 2.4L Hybrid using an A6MF2H transmission. There is no torque converter in this transmission. It does have an “engine clutch” and an “electrical motor” that sits in the area where the torque converter would be (Figure 1). The vehicle came into the shop with a “Stall on Engagement” complaint with repeated “Engine Clutch” burn out. In fact, when the trans was removed and disassembled, the engine clutch was smoked, and the clutch plates frozen/welded together.
At time of overhaul, it was decided to replace the engine clutch solenoid (EC-VFS) and line pressure control solenoid (LINE-VFS) as well as the engine clutch assembly.
On three short road tests after repairs the transmission would slip and flare up on engagement of the engine clutch so the transmission was removed once again to reveal a damaged engine clutch (Figure 2).
After going over the unit again with a fine-toothed comb, it appeared that the oil pump seal ring sleeve had shifted inward causing a bad seal for the rings. A new oil pump was ordered and confirmed the correct position of the seal ring sleeve. A new set of engine clutches were installed along with the oil pump assembly. The car was road tested and proper operation was now confirmed.
Carlos gave ATSG his experience as follows: This Hybrid system uses the electric motor machine to start moving this vehicle from a stop (forward or reverse) to a speed of 12km’s (7.5mph). The engine then starts, and the transmission applies the engine clutch to take over. As mentioned before, there is no torque converter in this vehicle. If the engine is running while the vehicle is stationary (battery charging), the Engine clutch must release while in drive at a stop.
The clutches in the vehicle that came to us were burned and welded together. This caused the car to stall aggressively when drive was selected (engine running only). If the engine was off during a start, things would appear to be fine until you let off the brake pedal, then it would chug like crazy! (Like a converter clutch stuck on).
Here’s why. Notice the steel sleeve in Figure 3. It should be flush with the aluminum housing of the pump.
If you look at Figure 4, you can see two sets of sealing ring markings (total of six) when there should only be three ring marks. The input shaft has three Teflon sealing rings on it. When the sleeve moved you can see where the Teflon rings made new marks. One new mark is missing because it was no longer riding in the sleeve. This is why it would fall out of gear and burn/weld the engine clutch.
Figure 5 shows the box and part number of the new Engine Clutch assembly.
- They use a conventional A6MF1 type 6-speed FWD trans with an $11,000 electric motor machine bolted between the trans and engine.
- The two pressure taps that are normally MARKED TCC RELEASE and TCC APPLY are now labeled EC (Engine Clutch) and the other (Lube).
As with many transmissions we deal with today, once certain types of work have been performed, TCM Learning must take place to eliminate any shifting issues. The following is O.E. information about TCM Learning with this vehicle.
When shift shock is occurred or parts related with the transaxle are replaced, TCM learning should be performed.
In the following case, TCM learning is required.
- Transaxle assembly replacement
- TCM replacement
- TCM upgrading
(1) TCM learning condition
- A. ATF temperature: 40 – 95°C (104 – 203°F)
(2) TCM learning procedure Driving learning
- A. Drive the vehicle through all gears at D range. Drive from stop to 1st to 2nd to 3rd to 4th to 5th to 6th with keeping fixed throttle open.
- B. Down shift from 6th to 5th, 5th to 4th, 4th to 3rd, 3rd to 2nd, 2nd to 1st.
- C. Repeat the above driving pattern four times or more. Upshift throttle open: 10-15%.