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USATransdoctor.com
These recommendations do not cover all possibilities. They are some things to check before you have your transmission rebuilt. Always check transmission fluid level first. Always run a scanner on any computer controlled transmission . On modulated transmissions make sure they have enough vacuum.

MERCURY VEHICLES
FIND THE MAKE OF YOUR VEHICLE
CLICK ON THE YEAR OF YOUR VEHICLE

*Bob Cat*	*1974-87 C3*	*1974-87 C4*
*Capri*	*1972-81 C4*	*1979-86 C3*	*1982-86 C5*
*Comet*	*1964-76 C4*	*1966-69 C6*
*Cougar*	*1967-81 C4*	*1967-78 C6*	*1982-86 C5*
	*1980-92 AOD*	*1993-1997 AODE/4R70W*	1999-2002 CD4E
*Grand Marquise*	*1983-92 AOD*	*1993-95 AODE*	*1996-2008 4R70W*
*Mariner*	2005-2008 CD4E
*Marquise*	*1983-86 C5*	*1983-86 C3*	*1983-86 AOD*
*Meteor*	*1965-80 C4*	*1966-72 C6*
*Montego*	*1968-76 C4*	*1968-76 C6*
Monterey	2004-2007 CD4E
*Mountaineer*	*1997-01 5.0L 4R70W*	2003-2008 5R55S ( No fill tube) 4.0 or 4.6L
*Mystic*	*1995-00 CD4E*
*Sable*	*1986-92 AXOD*	*1991-04 AX4S*	*1996-05 AX4N*
*Topaz*	*1987-94 ATX*
*Zepher*	*1976-83 C-3*	*1978-81 C4*	*1982-83 C5*

A4LD
This transmission is a rear wheel drive 4 speed automatic. Common symptoms are erratic shifting, hesitating going into gear and losing transmission fluid without a trace of a leak.

You have a modulator on the passenger's side of the vehicle pointing towards the driver's door. Pull the rubber line off the modulator and see it trans fluid comes out of the line. Now, if it does your modulator is no good. It can cause any of the above symptoms. If the vehicle speed sensor goes bad it can cause a no 4th gear symptom.
You also have band adjustments on this trans. Make sure they adjust them when your transmission is serviced.
I recommend that you always replace the boost valve when rebuilding any Ford transmission.

CD4E / G4AEL / 4EAT / AX4S /AX4S
The transmissions above are 4 speed front wheel drives. They are all computer controlled. If your transmission starts shifting erratic or not at all, then make sure you or a shop run a scanner on the vehicle.

You want to see if you have a sensor that has gone bad, causing your problems. The vehicle speed and transmission range sensors like to go bad on vehicles with these transmissions in them. So keep that in mind.

I recommend that you always replace the boost valve when rebuilding any Ford transmission.

E4OD / 4R70W / AODE
The transmissions above are rear wheel drive 4 speed automatics. they are all computer controlled. Common symptoms are overdrive light flashing, trans shifting erratic, slipping or not shifting at all. external sensors on the vehicle like the manual lever position sensor or throttle position sensor or vehicle speed sensor, quite often go bad causing these symptoms. Always run a scanner first to see if a sensor is causing your problem.

I recommend that you change the transmission fluid about every 12,000 to 15,000 miles. These transmissions can develop a symptom called torque converter chatter. The vehicle feels like you are running over railroad tracks when the torque converter locks up between 35-50 miles per hour. There are also valve body recalibration kits you can have installed to help prevent this before it occurs, or while your transmission is being rebuilt.

The manual lever position sensors like to go bad on vehicles with these transmissions.
I have seen a number of wire harness connectors that go bad and start seeping trans fluid up through the connector where the trans wire harness plugs into the transmission mostly on the 4R70W. Keep that in mind if you are having a problem. Upgraded Cast iron planetaries are now available for heavy trucks or motor homes with E40D style transmissions.
I recommend that you always replace the boost valve when rebuilding any Ford transmission.

C3 / C4 / C5 / C6
The transmissions above are rear wheel drive 3 speed automatics. Common symptoms are: erratic shifting, slipping or losing trans fluid without a source of a leak.

You have a modulator on the rear of the transmission on the C4 / C5 and the C6 units. The modulator is on the passenger's side of the transmission on the C3. Pull the vacuum line off the mod. If fluid comes out of the vacuum line your modulator is not good. Make sure your bands get adjusted when you service your trans. Make sure they do not lose your little spring and plunger that is under your filter on C4, C5 styles. This will cause unusually early and soft shifts.

ATX
This transmission is a front wheel drive 3 speed automatic. Common symptoms are: Early soft, late hard shifts or no shifts at all.

Listen up because this problem happens all the time. Always check the throttle pressure rod that goes from your transmission to your carburetor or throttle body linkage. This controls shift points and often the plastic little bushings that hold it on, get brittle from the heat, breaks into pieces and falls off causing symptoms above. Good Luck!
I recommend that you always replace the boost valve when rebuilding any Ford transmission.

AOD
This transmission is a rear wheel drive 4 speed automatic and shift timing is controlled by a throttle pressure rod or cable that connects from the transmission to the carburetor or throttle body.

Listen up again because this problem happens all the time. Always check the throttle pressure rod that goes from your transmission to your carburetor or throttle body linkage. This controls shift points and often the plastic little bushings that hold it on, get brittle from the heat, breaks into pieces and falls off causing symptoms above. Good Luck!
I recommend that you always replace the boost valve when rebuilding any Ford transmission.

AXOD
This transmission is a front wheel drive 4 speed automatic and shift timing is controlled by a throttle pressure cable that goes from the transmission to the carburetor or throttle body.

Always check this item first. If you do have to have your transmission rebuilt, make sure whoever rebuilds it, makes a modification called full time lube. This modification gives your transmission better trans cooler flow. You want to have at least 1 quart in 20 seconds, when vehicle is hot, on your return line from your trans cooler (radiator), to your transmission.
I recommend that you always replace the boost valve when rebuilding any Ford transmission.

4R44E / 4R55E
The transmissions above are rear wheel drive 4 speed automatics. They are all computer controlled. Common symptoms are, overdrive light flashing, transmission shifting erratic, slipping or not shifting at all.

External sensors on the vehicle like the throttle position sensor or vehicle speed sensor quite often go bad, causing these symptoms. Always run a scanner first to see if a sensor is causing your problem. If you screw the force motor in 1/2 turn the transmission has better shifts and engagements.
I recommend that you always replace the boost valve when rebuilding any Ford transmission.

5R55 N/S/W 5 Speed Rear Wheel Drive
These style transmissions do not have fill tubes to commonly check the trans fluid level. This transmission has a common problem of the case bores wearing out where the o/d - Intermediate servo pistons ride, causing various transmission slipping codes. There are also several different valve bodies and solenoid packs, Be careful.