The following information covers issues regarding incorrect transmission-to-TCM applications, the first being sprag and no-sprag units and the second dealing with incorrect gear-ratio interchange. The most-up-to-date transmission-ratio identifications are provided for Mitsubishi applications but not for Hyundai. We are working to acquire that information for a future publication.
The transmission or the transmission control module (TCM) has been replaced. The transmission now exhibits a neutral condition after it reaches 6 mph (late plastic-covered TCM with early transmission) or a harsh 2-1 coast downshift (early metal TCM with late transmission). The TCM description applies to Mitsubishi only. All Hyundai units have plastic-covered TCMs.
Midway through the 1997 model year Mitsubishi added a low sprag to the F4A40/50-series transmission. Hyundai followed Mitsubishi’s lead for the 1999 model year.
When the one-way clutch was added, the application of the low/reverse clutch also was changed. Transmissions equipped with the low one-way clutch keep the low/reverse clutch on at speeds of up to 6 mph, as shown in the clutch/solenoid application chart in Figure 1.
The transfer gear shown in Figure 2 fits a transaxle without a low sprag and is identified by the four mounting-bolt holes and the smoothly machined journal.
The transfer gear shown in Figure 3 fits a transaxle with a low sprag and is identified by the eight mounting holes and the splined journal to accept the low-sprag inner race. The sprag assembly is loaded into the underdrive ring gear, also shown in Figure 3.
The change in clutch-application strategy resulted in a change in the TCM. The TCM for a transmission with a low one-way clutch is NOT interchangeable with a TCM for a transmission without a low one-way clutch.
The TCM programmed for a transmission without a low one-way clutch has a metal cover (see Figure 4).
The TCM programmed for a transmission with a low one-way clutch has a plastic cover (see Figure 5).
Using an incorrect transmission/TCM combination will cause the complaints mentioned.
Use the correct transmission/TCM combination as explained previously.
How can you tell whether your transmission has a low sprag? Check the transaxle serial number on top of the case. If the serial number contains an A, as shown in Figure 6, the transmission does not have a low sprag and should have the TCM with the metal cover.
If the serial number contains a B, as shown in Figure 7, the transmission does have a low sprag and should have the TCM with the plastic cover.
TCM Part Numbers
- Mitsubishi without one-way clutch . . . . . . . .MD760927
- Mitsubishi with one-way-clutch . . . . . . . . . .MR357259
- Hyundai without one-way clutch, 2.4L, federal . . . . . . . . . .39110-38970
- Hyundai without one-way clutch, 2.4L, California . . . . . . . .39110-38317
- Hyundai without one-way clutch, 2.5L with TCS . . . . . . . . .95440-39012
- Hyundai without one-way clutch, 2.5L without TCS . . . . . .95440-39032
- Hyundai with one-way clutch, 2.4L, federal . . . . . . . . .39110-38298
- Hyundai with one-way clutch, 2.4L, California. . . . . . . .39110-38318
- Hyundai with one-way clutch, 2.5L, with TCS. . . . . . . . . .95440-39013
- Hyundai with one-way clutch, 2.5L, without TCS. . . . . . . . .95440-39033
Mitsubishi vehicles equipped with the F4A40/50 series transaxle may exhibit erratic shifts or diagnostic trouble codes related to gear-ratio errors, such as P0732, 2nd-gear-ratio error; P0733, 3rd-gear-ratio error; or P0734, 4th-gear-ratio error, after transaxle replacement.
The cause may be an incorrect transaxle, or that gear-train parts having ratios incompatible with the vehicle’s computer were installed.
Figure 8 breaks down the identification code dot-peened into the case.
Please make a special mental note about the speedometer-gear ratio, where it is explained that the letter Z indicates that the ABS wheel-speed sensors produce the vehicle-speed signal. The transmission will have a bolt-on plug instead of a speed sensor, as you can see in Figure 10. Do not think you can remove the plug and put a speed sensor in the transmission to be used in a vehicle that requires a speed sensor in the transmission. After it is installed into the car you will discover that you do not have any vehicle-speed signal. The reason is that there is not a drive gear on the differential to drive the speedometer gear you put into the case.
March 2007 Issue
Volume 24, No. 3
- Mitsubishi F4A40/50 Series: Updated Gear-Ratio Information
- Mitsubishi F4A40/50 Series: Erratic Shift and/or Gear-Ratio-Error Codes