Description
PATC 727518 Overdrive and Lock Up Kit.
Use this kit if you have replaced your 727 with a 518 transmission for the lock up and overdrive to engage automatically.
Or use this kit for your non lock up three-speed transmission as well, but with only one switch needed.
With this kit your new 518 transmission will have automatic shifts into overdrive and lock-up, no toggle switch needed.
Now with an adjustable pressure switch option. This is the kit for gas applications or diesels with a vacuum pump.
The instructions are at the bottom of this page.
(Not for “RE” transmissions)
The vacuum switch must be set to 16 – 18 inches of vacuum to engage the switches, they do not come with a precise preset.
This is how to replace your three-speed transmission with a 1995-back A518 overdrive transmission with a three-wire connector.
A 518 transmission has a 31% overdrive and will produce a 30 to 40% increase in gas mileage on the road over a three-speed transmission.
There are two wire 518 transmissions out there, these have a non-lock-up torque converter.
With this three-wire setup you have a four-speed transmission plus a torque converter lock-up feature. The extra gear is 3rd high range.
What we are doing here is control the overdrive and torque converter lock-up (which is normally controlled by the computer) using one vacuum switch and two pressure switches.
INSTRUCTIONS:
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#1. The center wire on the transmission is the hot wire and the two other wires are ground wires for overdrive control and the torque converter control. The front wire is the overdrive ground and the rear wire is the torque converter lock-up ground. You can get a three wire female connector from a junk yard or buy one from us. (Part Number: 79M) #2. Run a 12 volt fused wire, that turns on and off with the key, to the vacuum switch, then to the center wire on the transmission connector. The vacuum switch takes 16 – 18 inches of vacuum pressure to engage. And 3 inches or less of vacuum pressure to down shift/disengage and unlock the torque converter. (There’s a small mistake in the picture. The fuse goes on the battery side of the vacuum switch. Updated picture coming soon) #3. At the Governor Pressure Tap on the transmission, Port #4 per picture below, install a tee fitting for two pressure switches. The Governor Pressure Tap is located on the right side, at the upper rear of the main transmission case. The pressure switches then go on the tee fitting, installed in Port #4. (White plastic fitting from kit should preferably be replaced with metal tee fitting, not included in kit, not sold by PATC). #4. Run a wire from the front pin on the transmission connector to the overdrive pressure switch and a second wire from the rear pin on the transmission connector to the lock up pressure switch. The vacuum switch acts as a throttle position sensor and the pressure switch acts as a speed sensor. |
The #4 tap is the correct one.
Throttle Valve Adjustment
#5. A 518 transmission has a throttle valve cable (pressure cable), it must be hooked up and adjusted correctly. You can get the cable and brackets from a junk yard if needed. If you have a 727 transmission now, the linkage may work. The correct adjustment on the TV cable or linkage is minimum throttle pressure at minimum throttle. In other words no slack in the cable at idle and it must start to pull immediately off of idle.
Other Modifications
#6. When going from a 727 transmission to a 518 transmission the driveshaft will need to be cut about 3 and 1/2 inches. The swap may require some driveshaft tunnel modification on some cars. You will have to fabricate a new crossmember using the old crossmember ends because the transmission mount is lower on a 518 transmission than a 727 transmission. The stock Dodge truck mount is very tall. See pictures below. In the 1st picture notice the 518 transmission has a larger tail area. The second picture is the crossmember ends cut off ready to be reused. In the 3rd picture notice the transmission mount area has been lowered.
On the Adjustable Pressure Switches the “C”/common and “NO”/normally open posts do not get used.
The “NC”/normally closed post goes to the solenoid or 3 wire case connector pigtail.
As this is a normally closed circuit, once pressure builds up to the desired amount, the switches then engage the lock up and overdrive functions.
The 3 above pictures are a 1970 Dodge Dart Swinger A-Body.
Click Here, if you have a diesel without vacuum.
