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Author Topic: Transmissions: Overdrives: A-500 & A-518 Swap  (Read 68612 times)

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Transmissions: Overdrives: A-500 & A-518 Swap
« 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:

  • First Character = Number of forward speeds: "3" = 3 speed, "4" = 4-speed
  • Second Character = Type of duty: "0" to "9", with 9 being the strongest
  • Third Character = Type of drive: "R" = Real Wheel Drive
  • Fourth Character = Type of shift control: "H" = Hydraulic control, or "E" = Electric control

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:

  • A-500, 40RH, 40RE, 42RH and 42RE, 44RE - This series of transmissions (hereafter called A-500), is based on the Chrysler A-904 series transmission design.  Gear ratios are the same as 1980-up A-904-series transmissions. They share many of the same internal parts with A-904 series transmissions except for the OD tailshafts. The transmission pan has an identical shape to the A-904 series transmission pans, but it is much deeper.  The OD units will not interchange with tailshafts from A-904 series transmissions. A-904-style slip yoke will NOT work with these transmissions.
  • A-518, 46RH, 46RE - This series of transmissions (hereafter called A-518), is based on the Chrysler A-727 series transmission design.  Gear ratios are the same as A-727-series transmissions. They share many of the same internal parts with A-727 series transmissions except for the OD tailshafts. The transmission pan has an identical shape to the A-727 series transmission pans, but it is much deeper. The OD units will not interchange with tailshafts from A-727 series transmissions.
  • A-618, 47RH, 47RE - This series of transmissions (hereafter called A-618), came behind Cummins Diesel and V10 truck engines.  The internal parts are much heavier than the A-518, and they will interchange with A-518 parts. However, the A-618 Cummins bellhousing won't bolt to a small block Chrysler engine due to a different bellhousing bolt pattern. They are also unsuitable for car applications because the governor speeds are really low.  It has not been confirmed yet, but a few sites mention that the V10 bellhousing bolt pattern is the same as the Cummins pattern.

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 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.

  • The early 1991 and older non-lockup A-518s will have two pins towards the back of the main case just ahead of the rear oil line port. The input shaft will be splined all the way to the end.
  • 1995 and older lockup A-518s and all A-500s will have three pins towards the back of the main case just ahead of the rear oil line port. The last inch or so of the input shaft will also be smooth with no splines.

Swap Considerations:

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

  • Years to Look For - Look for 1995 and earlier versions because they are easy to wire. The 2-pin A-518 unit needs one fuse protected hot wire and one switch controlled ground wire to control OD. The three pin A-500 and A-518 units need one fuse protected hot wire, one switch controlled ground wire to control OD and one switch controlled ground wire for LU. They can either be manually operated with toggle switches or set up to operate automatically with a control kit from Performance Automotive and Transmission Center or Jet Performance Products.
  • Years to Avoid - 1996 and newer A-500s and A-518s are entirely computer controlled, and should be avoided.
  • Fabrication - If you're thinking of swapping an OD transmission into an M-body, you will probably have to widen the transmission tunnel at the rear crossmember to get the back of the unit up high enough so that the engine remains in its stock position and is not angled down. You will need to take a reference measurement with the stock transmission in place to make sure that you return the engine to its stock position.  Patrick Grossman used the distance from the steering center link (drag link) to the engine oil pan as a reference, and his swap returned the engine to within 1/8" of its original position. This will require fabrication skills as part of the floor and crossmember will have to be cut and rewelded.
  • Rear Crossmember - the rear crossmember will have to be cut and sectioned back together so that the rear mount position is relocated both farther back and lower to accomodate the bulkier OD tailshaft. Below is Mark Mullins' recap of the steps that he took to rework the rear crossmember of his Fifth Avenue:
    • The crossmember in the back of the tunnel that goes from side to side is the problem. You have to cut that piece out and weld a new one in.
    • I started by removing the front seats and rolling the carpet all the way back.
    • Next I drilled out the spot welds on the crossmember and sawz-alled it out.
    • Now only cut the crossmember from the point where it starts to follow the curviture of the tunnel.
    • Once that is out cut a hole in the top of the tunnel that follows the outline of the old crossmember.
    • Now you can fabricate a new piece of steel that'll take the place of the old crossmember that will sit up higher and flush with the bottom of the tunnel. I used 1" x 3" x 1/8" box tube I believe, might wanna check that. Weld it in and your all set.
    • Next you'll have to make a new trans mount. It's done pretty much the same way you made the top piece. Only differance is you need to make some mounting ears so you'll have a means of bolting it to the crossmember.
    • To secure the trans to the mount you just made use a universal GM trans mount. It's a piece of steel with a rubber isolater that'll work great. You might have to bore the holes out on it that bolt to the trans itself, but no more than a 1/4".
    • BTW - Don't cut the cross member out and think you could leave it like that. Some people have in the past while performing this swap. It weakens the integrity of the car.
    Below is Patrick Grossman's method for modifying the crossmember
    • I cut it out between the bolt holes for the lower removable portion of the crossmember.
    • Then I added 2 more holes further outboard of those holes
    • I welded some black pipe in them so the crossmember wouldn't crush when tightened
    • I then built a big, beefy bolt in crossmember out of 2"x 4" x .125" wall square tube to carry any load that crossmember carried.

  • Speedometer Cable - The speedometer cable and shift components will swap from the A-904 or A-727 to the A-500 or A-518.  However, if you have cruise control and you want to keep it, you will need a longer speedometer cable.  Use Pioneer part number CA3024, which is 20" longer than stock and has the correct ends.
  • Shift Linkage - Your existing shift linkage should work with either transmission.
  • Kickdown - Mark used his stock 904 kickdown with the A-500.  He just had to get a 4bbl arm from a cop car.  Patrick Grossman also used the 904 pieces with his Fifth Avenue. Depending on the year of the transmission used, kickdown linkage may be limited to the older one piece design or an aftermarket cable setup because there may be no provision for mounting the pivot needed for the three-piece setup.
  • Cooling Lines - OD transmissions have larger 3/8" cooling lines vs. 5/16" lines for the A-904 and A-727 transmissions. A heavy duty cooler is also recommended.
  • Driveshaft Slip Yoke - Both the A-500s and A-518s use the A-727 style slip-yoke. If you have a A-904 transmission, your slip yoke will be too small to fit.
  • Driveshaft Length - The additional length of the OD unit will require you to have your driveshaft cut down and rebalanced. A good truck shop can do this with the proper measurements.
  • Torque Converters - A-518s and A-500s do not use the same torque converters. A-500s use A-904-style torque converters, while A-518s use the A-727-style torque converters. Make sure that a non-lockup (NLU) torque converter is not mixed with a Lockup (LU) transmission and vice-versa. Also, a 360 (5.9) torque converter will have weights on it and a 318 (5.2) one won't. They can't be interchanged.
  • Lockup and OD Control - There are a few ways to control lockup and OD:
    • Mark Mullins pulled his cruise control out from under the hood, and wired OD to the existing wiring so that it is controlled by the cruise control switch on the turn signal stalk.  Lockup is wired to a separate 12v source and is controlled by a glow toggle switch on the left hand side of the dash.  Mark said: "It works out pretty well.  I only use lockup on the expressway. If you forget to turn off lockup and slow down to the point where the transmission downshifts on its own to second, the torque converter will shudder to no end.  You have to be careful of that because it will eventually damage the transmission and/or torque converter.  Overdrive, or 4th gear, has nothing to do with the kickdown.  Since OD is electronically controlled by a 12v source, if it is left on, the transmission will immediately shift to 4th once it shifts into 3rd.  Also, if OD is left on, it will not down shift via the kickdown.  It will only downshift when slowing down.  Patrick's automated setup using engine vacuum is really the way to go."
    • Patrick Grossman used a different method: He went to a local transmission shop, and bought 2 normally open oil pressure switches. Following the instructions on the  PATC website, he ran a 3/16" line off of the governor port to a tee fitting and installed a 48PSI and 50 PSI switch. He ran the OD control to the 48PSI switch and the lockup ground to the 50PSI switch. These switches are used in GM TH350's, and cost him $17 for both. He then ran the positive lead to a GM vacuum switch (Standard Motor Products P/N VX2), which was $37 at the local parts store. So far, for a factory connector, he is thinking that an '83-86 chevy van connector from a junkyard seems to be the best bet. There is a newer GM vacuum switch that uses a standard weatherpack connector, and he's researching that now. For the OD cancel switch, he used his rear amp switch, which wasn't being used.
    • Moparts member DonOremus used a similar method to control the A-518 that he installed in his big block 1969 Dodge Super Bee: He ran a GM vacuum switch in the fused key-on 12volt supply to the center terminal of the transmission. On the ground sides (the front and rear terminals) He has the Lockup wire going through a normally closed relay hooked up to the brake light switch that opens (unlocks converter clutch) when the brakes are applied. He also has a couple of manual rocker switches as well to add a little more control.  He uses the rocker switches to shift between the two, but the GM vacuum switch automatically kicks OD and lockup off if when he hits the throttle hard.


  • A-500 & A-518 Pictures and Dimensions
  • Photos below courtesy of Mark Mullins © 2008 Mark Mullins
    • Interior showing floor and crossmember cuts with A-500 in place. 
    • Interior showing crossmember reinforcement and rewelding floor. 
    • Interior showing final welding and closing of floor.
    • Underneath showing crossmember cuts with A-500 in place.


« Last Edit: February 19, 2011, 00:29:49 by Reggie »
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