Farley`s Dodge Diplomat Forum

Forum Index => The Library => Topic started by: Reggie on January 19, 2008, 00:01:17

Title: Transmissions: Overdrives: A-500 & A-518 Swap
Post by: Reggie on January 19, 2008, 00:01:17
Chrysler A-500 and A-518 Four Speed Automatic Transmission Swap


Chrysler automatic overdrive (OD) transmissions are four-speed transmissions based on the old Torqueflite three speed design, but with .69:1 overdrive units located in their tailshaft sections.  Production of OD transmissions started around 1988 in Dodge trucks and vans.   ODs were also used in Jeep vehicles.  As far as it is known, they were never installed in passenger cars from the factory. All A-500 and A-518 series tranmissions share the same bellhousing bolt pattern, and they will bolt up to any 273, 318 (LA and Poly "A" ), 340 or 360 engine (hereafter called LA pattern).  They can also can be used with big block B/RB engines with special adapters.  They will not bolt up to Slant 6 engines.

Originally, Chrysler identified its automatic transmissions using a letter followed by a three digit number, such as "A-904" or "A-727".  Chrysler followed this identification method with its early OD transmissions.  The A-904-based overdrive was called the A-500, while the A-727-based overdrive was called the A-518.  In 1992, Chrysler began designating all of its transmissions with a series of alphanumeric values based on the number of forward gears, the type of duty, the application and the method of control.  The identification method is as follows:

Transmission Identification Codes:

Thus, a "42RH" designation would be for a four speed, light duty, rear wheel drive transmission that is hydraulically controlled.  A "42RE" designation would mean  four speed, light duty, rear wheel drive transmission that is electronically controlled. Chrysler developed three types of automatic OD transmissions based on the old Torqueflite design:

Types of Overdrive Transmissions:

Below are Chrysler automatic overdrive (OD) transmission gear ratios:

Overdrive Transmission Gear Ratios:

TransmissionA-500 A-518 A-618
First 2.74 2.45 2.45

Overdrive Units:

A-500 and A-518 tailshafts both contain the same .69:1 overdrive unit, and they will interchange with each other.  However, there are variations in the number of clutches between V-6 and V8 42RH/RE applications and V8/V10/Diesel 46/48RH/RE applications.  The OD tailshafts will not fit 904-series or 727-series transmissions due to different bolt patterns and oil passages. They are also much bulkier than A-904 or A-727 tailshafts, and the location of the mounting pad is farther back than A-904 or A-727 transmissions.


OD transmissions came in both lockup (https://www.dippy.org/forum2/index.php/topic,16.0.html) and non-lockup versions. Non-lockup versions of the A-518 were available at least through 1991. A-500 transmissions were only offered with lockup.

Swap Considerations:

We will only discuss the A-500 and A-518 series transmissions here, since they have the LA bolt pattern.