Transmission

by Michael Decipha Ponthieux
Posted: 4-28-2013
Last Updated: 7-5-2016

Basic Transmission Operation

The ECU can only control the 2 shift solenoids A and B, TV-Line pressure via the EPC solenoid, and the TCC - Tq Converter Clutch.
All other operations are done mechanically by the transmission and valve body.
E4OD / 5R55 and newer transmission's also have a CCS - Coasting Clutch Solenoid (sometimes refered to as solenoid 3 or solenoid C), the ecu
powers that solenoid when O/D is disabled by the TCS - transmission control switch on the shift lever.
WARNING: Hot-wiring the CCS when in overdrive will cause a parking shaft to trans case hard lock and will damage the transmission.


Automatic Transmissions Sensors:
OSSOutput Shaft Sensorecu use's to calculate the speed of the output shaft
VSSVehicle Speed Sensorequipped on all 98 and older vehicles, some 99+ vehicles do not have a VSS
TSSTurbin Shaft Speedecu uses to calculate the speed of the input shaft, used on E4OD, 5R55 and newer transmissions
MLPSManual Lever Position Sensorecu uses to know the position of the gear shifter, 98 and newer have 6 switches, older MLPS is analog 0-5v
TCSTransmission Control Switchthe switch on the gear shifter lever, disables O/D and engages the CCS on those so equipped
**Click on MLPS above to view the MLPS wiring diagram

Valve Body

The valve body is the central operations of the transmission. The valve body directs fluid flow to specific passages to engage/disengage
frictions, etc.. blah blah blah, yadda yadda yadda and so on...

EPC Solenoid

The EPC "electronic pressure control" solenoid is a simple amperage based flow valve. The more amperage the valve is given the more closed the orifice allowing less flow.
With no power applied to the EPC it is in a normally open state giving 100% line pressure. Not all EPC's are identical, the nagivator has an EPC with more flow capabilities
than the more common EPC's on most other vehicles. When changing EPC solenoids for the higher flowing Navigator EPC, it is necessary to let the ECU know that you have
changed the flow characteristics of the EPC via the transfer function FN620 - Variable Force Solenoid Transfer the standard EPC transfer is as follows
PSIAMP
85.000.298
75.000.420
50.000.635
20.000.835
3.500.922
0.001.000

...now on to the good stuff

Tuning

To lock the trans in 3rd for Dyno Tuning see the Tuning Tips & Methodology Write Up.

TV Pressure

Dynamic TV pressure is calculated by engine torque, the ecu uses the current airmass from the MAF Sensor to calculate engine torque. That value is compared to the engine
torque table FN1615A - Engine Torque Table, which is scaled by Load and RPM, if the actual torque is less than this table then you get excess pressure,
If the actual torque is greater than this table then you get less pressure. This table must be manually dialed in by the tuner.

The ecu is constantly trying to adjust tv pressure to get the engine tq to equate the expected torque in the torque table, this is actually a very efficient way of controlling tv pressure
However, any changes to the engine such as injectors, MAF, etc.. can skew the expected engine torque table and cause premature transmission wear due to too much or too little
tv pressure. Therefore, I HIGHLY recommend loading in the values below and using the Engine TQ Table to adjust the shift firmness.
EEC-IV & EEC-V
PIDParameterRecommended ValueComment
VS21PI2 - 1 MAX SPEEDMPH @ 5k rpm in 1stECU REFERENCES TO CALCULATE WHICH GEAR TO SHIFT INTO WHEN POWERED ON WHILE THE VEHICLE IS MOVING
VS32PI3 - 2 MAX SPEEDMPH @ 5k rpm in 2ndECU REFERENCES TO KNOW WHICH GEAR TO ENGAGE WHEN POWERED UP WHILE VEHICLE IS MOVING
VS43PI4-3 Max SpeedMPH @ max rpm in 3rdthis is used as the above, but is also used to Disable the TCS o/d cancel when vehicle speed exceeds this value
TMVEDNDOWNSHIFT DELAY0.200DOWNSHIFT DELAY TO RAMP PRESSURE for 4r70w/aode ONLY, E4OD must be set to 1.0 to prevent damage.
TMVEUPUPSHIFT DELAY0.200UPSHIFT DELAY TO RAMP PRESSURE for 4r70W/aode ONLY, E4OD must be set to 2.5 to prevent damage.
TMVETOUPCT UPSHIFT DELAY1UPSHIFT DELAY AT CLOSED THROTTLE (DURING TIP OUT)
SW_STALTVFN616 OVERRIDE1SWITCH TO DISABLE DYNAMIC TV PRESSURE AND FORCE FN616F AND FN616R TO BE USED
TMSQ23P43rd Gear UPSHIFT DELAY2.0MINIMUM TIME IN 2nd BEFORE UPSHIFT IS ALLOWED
TMSQ34P44th Gear UPSHIFT DELAY3.0MINIMUM TIME IN 3rd BEFORE UPSHIFT IS ALLOWED
TMSQ21P12nd Gear Downshift DELAY1.5MINIMUM TIME IN 2nd BEFORE Downshift to 1st IS ALLOWED
TMSQ32P23rd Gear Downshift DELAY1.0MINIMUM TIME IN 3rd BEFORE Downshift to 2nd IS ALLOWED
MNOSSPEROSS MIN PERIOD100MINIMUM OSS PULSE TIME CLIP - SET TOO HIGH WILL CAUSE DOWNSHIFT TO 3RD AT HIGH SPEEDS
RTNVMXMAX N/VS CORRECTION1MAXIMUM ADAPTIVE VEHICLE SPEED
RTNVMNMIN N/VS CORRECTION1MINIMUM ADAPTIVE VEHICLE SPEED
GR_SEQ_4214 - 2 SHIFT 1ST STEP31ST STEP IN 4 - 2 GEAR DOWNSHIFT, RECOMMEND TO NEVER ALLOW 4TH TO 2ND SHIFT WITHOUT GOING THROUGH 3RD
SRLUMNMIN SPD RATIO TO LOCK CONVERTER0.930MINIMUM SPEED RATIO TO ALLOW THE TCC TO LOCK - THIS WILL REDUCE EXCESSIVE CLUTCH USAGE FOR HIGH STALL CONVERTERS
UNLKDLYTMTCC CT UNLOCK DELAY64THE CLOSED THROTTLE TIME DELAY BEFORE THE TCC IS UNLOCKED
++|TVPMINPT_11ST GEAR MIN TV PT0.0MINIMUM TV PRESSURE CLIP IN 1ST GEAR AT PART THROTTLE
++|TVPMIN11ST GEAR MIN TV0.0MINIMUM TV PRESSURE CLIP IN 1ST GEAR
++|TVPMINST_11ST GEAR MIN TV NON SHIFT35.0MINIMUM TV PRESSURE CLIP IN 1ST GEAR NON SHIFTING
++|TVPMINPT_22ND GEAR MIN TV PT8.0MINIMUM TV PRESSURE CLIP IN 2ND GEAR AT PART THROTTLE
++|TVPMIN22ND GEAR MIN TV0.0MINIMUM TV PRESSURE CLIP IN 2ND GEAR
++|TVPMINST_22ND GEAR MIN TV NON SHIFT35.0MINIMUM TV PRESSURE CLIP IN 2ND GEAR NON SHIFTING
++|TVPMINPT_33RD GEAR MIN TV PT8.0MINIMUM TV PRESSURE CLIP IN 3RD GEAR AT PART THROTTLE
++|TVPMIN33RD GEAR MIN TV0.0MINIMUM TV PRESSURE CLIP IN 3RD GEAR
++|TVPMINST_33RD GEAR MIN TV NON SHIFT40.0MINIMUM TV PRESSURE CLIP IN 3RD GEAR NON SHIFTING
++|TVPMINPT_44TH GEAR MIN TV PT15.0MINIMUM TV PRESSURE CLIP IN 4TH GEAR AT PART THROTTLE
++|TVPMIN44TH GEAR MIN TV20.0MINIMUM TV PRESSURE CLIP IN 4TH GEAR
++|TVPMINST_44TH GEAR MIN TV NON SHIFT45.0MINIMUM TV PRESSURE CLIP IN 4TH GEAR NON SHIFTING
TVPMIN_ENGTV MIN CLIP4MINIMUM TV PRESSURE CLIP (GLOBAL) - USED EVEN AT IDLE DO NOT EXCEED 12 UNDER ANY CIRCUMSTANCES
++|TVPMINPT_ENGTV MIN CLIP PT20MINIMUM TV PRESSURE CLIP AT PART THROTTLE (GLOBAL)
++|SCINT11ST GEAR STATIC OFFSET0STATIC OFFSET PRESSURE IN 1ST GEAR
++|SCINT22ND GEAR STATIC OFFSET-10STATIC OFFSET PRESSURE IN 2ND GEAR
++|SCINT33RD GEAR STATIC OFFSET-4STATIC OFFSET PRESSURE IN 3RD GEAR
++|SCINT44TH GEAR STATIC OFFSET-1STATIC OFFSET PRESSURE IN 4TH GEAR
++|SCSLP11ST GEAR STATIC SLOPE0.219STATIC TQ MULTIPLIER FOR NON-SHIFT CAPACITY - REDUCING THIS VALUE INCREASES TV PRESSURE
++|SCSLP22ND GEAR STATIC SLOPE0.270STATIC TQ MULTIPLIER FOR NON-SHIFT CAPACITY - REDUCING THIS VALUE INCREASES TV PRESSURE
++|SCSLP33RD GEAR STATIC SLOPE0.301STATIC TQ MULTIPLIER FOR NON-SHIFT CAPACITY - REDUCING THIS VALUE INCREASES TV PRESSURE
++|SCSLP44TH GEAR STATIC SLOPE0.320STATIC TQ MULTIPLIER FOR NON-SHIFT CAPACITY - REDUCING THIS VALUE INCREASES TV PRESSURE
++SCSLP1SDDOWNSHIFT SLOPE IN 1ST0.039STATIC TQ MULTIPLIER FOR SHIFT CAPACITY - REDUCING THIS VALUE INCREASES DOWNSHIFT PRESSURE
++SCSLP2SDDOWNSHIFT SLOPE IN 2ND0.250STATIC TQ MULTIPLIER FOR SHIFT CAPACITY - REDUCING THIS VALUE INCREASES DOWNSHIFT PRESSURE
++|SCSLP3SDDOWNSHIFT SLOPE IN 3RD0.250STATIC TQ MULTIPLIER FOR SHIFT CAPACITY - REDUCING THIS VALUE INCREASES DOWNSHIFT PRESSURE
++|SCSLP4SU4TH GEAR UPSHIFT SLOPE0.078STATIC TQ MULTIPLIER FOR UPSHIFT CAPACITY - REDUCING THIS VALUE INCREASES TV PRESSURE
++|SCSLP2SU2ND GEAR UPSHIFT SLOPE0.180STATIC TQ MULTIPLIER FOR UPSHIFT CAPACITY - REDUCING THIS VALUE INCREASES TV PRESSURE
++|SCSLP3SU3RD GEAR UPSHIFT SLOPE0.199STATIC TQ MULTIPLIER FOR UPSHIFT CAPACITY - REDUCING THIS VALUE INCREASES TV PRESSURE


NOTE: ++| = are disabled by the SW_STALTV being enabled.
EEC-V - Additional Scalars
PIDParameterRecommended Value
DSRUE2Shift Slip% 2nd End0.300
DSRUE3Shift Slip% 3rd End0.250
DSRUE4Shift Slip% 4th End0.040
DSRU2Shift Slip% 2nd0.005
DSRU3Shift Slip% 2nd0.099
DSRU4Shift Slip% 2nd0.005
TMCLUP2Time CL Upshift 2nd2.500
TMCLUP3Time CL Upshift 3rd1.400
TMCLUP4Time CL Upshift 4th1.400
TMOLUP2Time OL Upshift 2nd0.200
TMOLUP3Time OL Upshift 3rd0.600
TMOLUP4Time OL Upshift 4th0.600
TCDNONDownshift Complete Time1.350
TCUPON12Upshift Complete Time 2nd2.200
TCUPON23Upshift Complete Time 3rd2.100
TCUPON34Upshift Complete Time 4th1.800
TCD43ONDownshift Complete Time 3rd1.000
TCDN1ONDownshift Complete Time 1st0.700

With the above values set, you can adjust shift firmness by using the engine tq table ONLY. Reducing the engine tq table will reduce shift firmness, increasing the tq table will increase shift firmness.

SW_STALTV / Disable Dynamic TV Pressure

Dynamic TV pressure can be disabled by forcing the ecu to use the FN616 function(s) for all TV pressure.
Disabling Dynamic TV Pressure is achieved by changing the scalar SW_STALTV from 0 (disable) to 1 (enable), as recommended above in the table.
Keep in mind when doing such, you loose all the gear specific transmission clips denoted by ++| in the table above.
If you have disabled dynamic tv pressure then its imperative that you put realistic values in the FN616F (forward tv pressure) and FN616R (reverse tv pressure) functions.
Note: It is NOT IDEAL to override tv pressure on turbocharged vehicles since load is a HUGE factor in tv pressure requirements on turbocharged vehicles.

--FN616F--
TP_RELPSI
5.1080
1.5070
1.3266
1.1262
0.5640
0.1030
0.0410
0.0010

Note: the bottom tv pressure is set to 10 at closed throttle, although that is slightly higher than you want, it is required to prevent gear drop-out (neutral drops)
when decelerating in gear at closed throttle.

Reverse requires a tad more pressure so for reverse you can make it look like this
--FN616R--
TP_RELPSI
5.1080
1.5070
1.3266
1.1262
0.5645
0.1035
0.0415
0.0015


As a general rule of thumb i never exceed 75-80 psi at WOT, in many factory calibrations its typical to reach 90+ tv pressure for a few seconds when at WOT while engine torque stabilizes.

Typically I find most transmissions like about 5 PSI more tv pressure than required to hold the clutch, avoid excessive tv pressure. Slightly less tv pressure is safer than slightly too much.

Speedometer / Calculated Vehicle Speed Calibration - N/V Base

In all 1995 and newer vehicles, the ecu reverse calculates vehicle speed based on the output shaft speed. This payload is VSBART_RT. VSBART_RT is used for all shift scheduling calculations. In order for the ecu to accurately calculate VSBART_RT (calculated vehicle speed) the following parameters must be set correctly.
PIDParameterValueComment
NVBASERPM / MPH Ratiosee chart belowthis scalar is the actual rpm divided by vehicle speed when the transmission gear ratio is 1:1 (typically 3rd gear)***
NOVCNTVSS Update Samplesvehicle speed sample rate to update learned
vehicle speed, either 4 or 10
NVBASE_X_NVCVSS Constantthis scalar should equal NVBASE*NOVCNT
***IF your transmissions does not have a 1:1 Ratio you will need to cross calculate your NVBASE value

The following is an N/V Base reference chart with the more commonly used N/V Base values.
N/V Base Reference Chart
NVBASEAxle RatioTire Rev/MileComments
372.7381294-04 stang
4098 mark8 all-(225/60/16 w/ 3.27 & 3.08)
433.55 or 3.73733 or 7032000-2004 Lightning & Harley F-150
443.2781203-04 stang
44.53.0881294-95 stang
4799-04 F-250 (all)
483.5581203-04 stang
50.53.73810estimated
54.54.10812estimated
Note: VSBAR is the actual VSS sensor reading which is used for the clusters speedometer on all 98 and older vehicles including some newer vehicles such as the 99-04 f-250 trucks. In those cases, the worm gear affixed to the vss sensor on the tail shaft housing will need to be changed for the speedometer to be accurate. Note that the VSS (VSBAR) is only used by the ecu for speed functions and limiters.
VSBART_RT is reverse caculated vehicle speed from the OSS and is used for all shift scheduling on all automatic ecu controlled transmissions.

In all OBD-II ford ecu's that have PCM calculated vehicle speed (most all 99+ fords), the 4 parameters that calculate vehicle speed are:
OSSoutput shaft speed on the tail shaft of the transmission
Gear Ratio'sThe transmission gear ratio's in the calibration
Rear End RatioThe rear end gear ratio in the VID BLOCK, this can be disabled to use the cal RT_AXLE
Tire REVS/MileThe amount of revolutions per mile stored in the CALIBRATION
**Note: Ford has a tire/rev offset of 1.0343%, when calculating actual tire revs per mile, increase the result by 1.0343% to be inputted into your tune for your speedometer to be 100% accurate.

The VID Block is the Vehicle Identification Block, it contains information regarding the vehicle including the tire rev's per mile and the rear end gear ratio. Even though all calibrations have a gear ratio and rev/mile scalar in the calibration constants, in most factory calibrations the VID Block is only used to provide the rear end gear ratio for the actual cluster vehicle speed calculation. This allows shops to reprogram the VID block for rear end gear changes WITHOUT having to have access to the strategy's calibration. Keep this in mind as your calibration constants for gear ratio and tire revolutions per mile may not be the same as the VID Blocks data. The tire rev per mile in the VID is ONLY for information purposes only, I am not aware of it actually being used on any factory calibration for the vehicle speed calculation. If you would like the ecu to reference the PCM's gear ratio calibration constant in lieu of the VID Block gear ratio, the VID Block Speedo Calculation scalar must be disabled in the calibration =0 instead of the stock value of 1=enabled. However, I do not recommend using the calibration value when you can simply just change the VID blocks value.

For all 98 and older ecu's, the PCM does not calculate the vehicle speed for the cluster display. Instead, the transmission is equipped with a VSS - vehicle speed sensor that is fed directly into the cluster, ecu, and cruise control module. When changing tire size or gear ratio's on a pre 99 ford, the VSS must be removed and a correct tooth count ring be installed on the VSS.

Shift Scheduling - RPM & Vehicle Speed

The upshift schedules are controlled by the sealevel shift functions
which are scaled by relative throttle and inferred vehicle speed
The downshift schedules follow the same principles and are the functions:
The ecu reverse calculate's the vehicle speed from the tire speed through the OSS sensor, this is a dataloggable payload VSBART_RT, this is the actual
vehicle speed used in the shift functions, the VSS sensor "VSBAR" IS ABSOLUTELY USELESS AND NOT used for shifting
The objective when tuning shifts is to get the transmission to shift fast which doesn't necessarily mean hard.
A fast shift reduces slippage, where as a hard shift forces engagement.
Quick Shift Scheduling Adjustment for Tire/Gear Changes
Whenever you update the nvbase calculation or change gear ratio or tire size you should make a general ballpark adjustment to get the shifts to occur at the same rpm they used to. You can do so by simply dividing the old tire size by the new and multipliying that by the old gear ratio divided by the new to come up with a correction factor. Then simply multiply the shift functions by that factor for a general rough ballpark estimate. Then simply dial in the shift speeds to your desired liking.


I will give you a quick run down, for example:

old tire 225/60/16==26.6" overall diameter, and rear gear 3.08
6000 rpm in 3rd old setup == 154.4 mph

new tire 275/45/18==27.7" diameter and rear gear 3.73
6000 rpm in 3rd on new setup == 132.8

27.7/26.6 = 1.041 your shifts need to occur 1.041 mph faster to shift at the same rpm
3.08/3.73 = 0.8257 mph slower to shift at the same rpm


1.041 * .8257 = 0.8595, go multiply the upshift functions by .86 and you will have a good start to begin tuning the shift points
to double check, the vehicle speeds at 6k rpm will also provide the same factor, 132.8/154.4 == 0.86

dont forget to copy the modified upshift schedule to the downshift and subtract 10mph for a quick and easy rough adjustment
WOT Shifting
WOT shifting follows the same basics as part throttle shifting but also uses the WOT shift rpm scalars NE12S, NE23S, NE34S. When the ecu reaches these RPM's the shift is then commanded. Its ideal to command the shift 300 rpm or so before the actual shift will complete. Be sure the shift scheduling upshift and downshift functions have the correct vehicle speed entered for the shift to occur at these rpms. You will either need to calculate the vehicle speed or datalog and see at what vehicle speed the vehicle is at during these conditions to update the functions accorindly. Keep in mind, the shift schedule functions are based on relative throttle position, thus closed throttle = 0.000 and WOT = approx. 3.200 to 3.800 volts.

Note: Its common for 1st gear to be pedaled during wheel spin on launch. Therefore, I recommend setting 2.0 Relative TP and above to the WOT Shift speed in the FN12S upshift function. Failure to do so will result in a 1-2 upshift when the throttle is feathered during wheel spin on launch significantly hurting 60' times.

Erratic Shifting Issues - (MLPS FAILURE)

Its not uncommon to encounter an erratic 4 - 3 and 3 - 4 shift while at a steady cruise, this is typically due to a bad MLPS sensor found on pre 98 model vehicles. Ford redesigned
the MLPS for 98+ vehicles to prevent this issue from occuring. If you encounter this problem it is highly recommended to replace the MLPS. Datalogging the actual MLPS sensor
voltage input to the ecu via the payload "INDS" will make it evident if this is the issue.

Another reason one might have an erratic 4 - 3 downshift while coasting/decel is due to pressure loss, a leaking valve body gasket, low transmission fluid level, or insufficient tv
line pressure should be suspect AFTER the MLPS has been verified to be functioning correctly.

TCC - Torque Converter Clutch Lock/Unlock Scheduling

The TCC scheduling follows the same scaling of TP vs VS as does the shift scheduling.
The lock schedule functions are: FN2LS (2nd gear lock), FN3LS (3rd gear lock), FN4LS (4th gear lock).
The unlock schedule functions are: FN2US (2nd gear unlock), FN3US (3rd gear unlock), FN4US (4th gear unlock).
NEVER SET THE UNLOCK HIGHER THAN THE LOCK!!!! This will cause the ECU to lock/unlock the TCC very rapidly.


On every vehicle I tune I always, disable the tcc from locking between 0.7v - 3.0v of relative TP.
I always set 3.0v+ to the vehicle speed (calculated from RPM) that the engine makes peak torque.
I always set 0-0.7v on a linear slope from 1200 rpm to 2200 rpm.

To put the above mentioned values into context, a typical stock 3.27 rear gear 4r70w equipped vehicle with 225/60z16 tires I do like this:
--FN2LS--
TP_RELVS
5.152
3.052
3.0127.5
0.7127.5
0.719.5
0.019.5

TCC remains locked at closed throttle

In all of my tunes I prefer the TCC to stay locked at closed throttle, keep in mind you must DIAL IN THE TCC LOCK FUNCTIONS
otherwise you will have issues with clunking, stalling, etc...

To force the TCC to stay locked on EEC-V you would adjust the following

Force CT - TCC Lock on EEC-V
ScalarRecommended ValueComments
VSMXLKDLY34Minimum MPH for the TCC to remain locked at CT
TPUNBRK0.00Max TPREL to unlock when brake is pressed
TPUNCT0.00TPREL to unlock at closed throttle

Transmission Engagement Enrichment (to prevent stalling)

It's common for an engine to lean out when the transmission is engaged, the ecu has a function to combat this that conveniently adds fuel
when the transmission is engaged. That fuction is FN371 it's usually always neccessary to demand enrichment when the transmission
is engaged to prevent stalling or severe idle drop.

I recommend the following value's for initial base tunes, adjust accordingly there after.

------FN371------
ECTxLambse
655340.922
1200.922
1000.898
500.801
300.699
-655360.699
-655360.699
-655360.699


If the engine rpm's drop too much (usually when cold) you may need to add even more fuel by demanding even lower values of up to 0.602 at lower temps.
At warmer engine temps, usually this function can be reduced to 1.000 IF the engine allows. This function will decay enrichment at the rate of FN393.
Note: The xLambse is a multiplier on Lambse thus lower values will INCREASE (richen) fuel and higher values with DECREASE (lean) fuel .

Not only does fuel play a huge factor in transmission engagement, the ISC Drive Multiplier table will as well. Be sure to dial in the
ISC Drive Multiplier table - FN1862D as discussed in the
Startup Enrichment Write Up

Datalogging

The PIDs you want to log for dialing in the transmission are:
PIDParameterDetails
TP_RELRelative TPRelative throttle position, tp subtracted from ratch, ratch is the lowest tp voltage since ecu powered on
TV_PRESEPC PressureThe actual pressure delivered to the trans, Static+Dynamic
TV_STATStatic Pressurecalculated static tv pressure
TV_DYNDynamic Pressurecalculated dynamic tv pressure
TQ_NETNet TorqueCalculated net engine torque
BCSDCTCC DCTorque Converter Clutch Duty Cycle
SLIP_DESTCC Slip DesiredThe slip the ecu is commanding, values from 0-1024, 0=no slip, 1024=full slip
GR_CMGear Commanded tcc lock =+1
NOBARTOSS SpeedOutput shaft speed
VSBAR_RTCalculated Vehicle SpeedVehicle speed used for shifting, reverse calculated from output shaft speed
SPD_RatioConverter Speed RatioConverter ratio engine rpm over output shaft speed
DELTA_RATIOShift RatioGear change ratio during a shift
TOTTrans Oil TempActual temperature of the transmission fluid in the pan

Maintenance

NEVER change the trans fluid on a transmission with high mileage ( >100k miles) which hasn't been properly serviced. Changing
the transmission fluid on high mileage neglected transmissions will cause premature failure. If you have changed the fluid, do not
replace the filter. Likewise, if you have an external trans filter but excess mileage with neglect, its recommended to replace the filter only.
I only recommend using Mercon V transmission fluid in all 4r70w transmissions. Be sure to flush out the old fluid and change the filter before
changing fluid types. Also note, Mercon V is not recommended for manual transmissions that utilize ATF.
For all 4r70w transmissions, Ford recommends using only Mercon V trans fluid as factory equipped
For all E4OD/4r100 transmissions, Ford recommends using only Dex/Merc trans fluid as factory equipped.
Using the incorrect spec trans fluid may cause torque converter failure and increased transmission slippage.
Lucas Tranmission fix is a great additive I recommend for all high mileage transmissions when fluid is needed.
Note: Most transmissions have a reuseable transmission pan gasket, and most converters have a drain plug to allow full oil replacement.


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