A/T - A500 Service Procedures
SIL: 88-34 (Oct)SUBJECT: CHRYSLER A500
SERVICE PROCEDURES:
This bulletin provides a description of the A 500 four-speed automatic overdrive transmission, as well as diagnosis and repair procedures to service this transmission.
The front portion of this unit is a modified A 999 three-speed loadflite automatic transmission. The rear unit, or overdrive, replaces the extension housing and provides a fourth gear with an economy gear ratio (.69 to 1.0) (Figure 1).
A lockup torque converter which is electronically controlled and hydraulically activated, will also be used with this transmission. Fourth gear (overdrive) and lockup will only occur during certain conditions determined by the SMEC (Single Module Engine Controller).
When the vehicle is traveling in third gear over 25 miles per hour, the SMEC uses the following information to allow the shift: The SMEC checks the coolant sensor signal for a 60-degree Fahrenheit minimum temperature. It also checks the engine speed sensor, the vehicle speed sensor, the throttle position sensor, and the map sensor.
ELEMENTS IN USE AT EACH POSITION OF THE SELECTOR LEVER
There is an overdrive off switch located on the instrument panel. The switch is marked O/D OFF and incorporates a pilot light to indicate when the switch has been activated. When activated, the switch will prevent shifts into overdrive and lockup. This is desireable when towing, driving in hilly terrain, or any other driving conditions that make overdrive unsuitable. Activating the switch again will restore the automatic overdrive operation. The switch will reset for operation when the key is turned off.
Other features in conjunction with this unit include:
^ The output shaft of the three-speed section will now be referred to as the intermediate shaft.
^ The three-speed section rear drum is retained on the support with a snap ring.
^ The governor and speedometer drive have been relocated to the rear of the output shaft.
^ The overdrive case now contains two output shaft bearings. One is the output shaft front bearing, and the other is the output shaft rear bearing.
^ There are no rotating seal rings or pressurized oil for the overdrive and direct clutches in the overdrive housing. The governor is the only component receiving pressurized oil through slip-fit tubes. Pressurized oil for the overdrive lubrication circuit is supplied through the intermediate shaft.
^ Governor pressure and overdrive pressure taps are provided in the rear of the main case for in-vehicle transmission pressure testing.
^ The valve body has been modified by adding several new valves. There's an overdrive solenoid a 3-4 shift valve, a 3-4 timing valve, a 3-4 accumulator, and a 3-4 shuttle valve. Once in fourth gear, the lockup solenoid, lockup valve, and lockup timing valve accomplish the hydraulics to lock the converter turbine to the torque converter housing.
^ The direct drive and overdrive gear ratios are supplied by a third planetary gear set, a direct clutch, an overdrive clutch, and an overrunning clutch. A very strong spring, rated at up to 800 pounds (5,516 KPA), holds the sun gear to the annulus for direct drive. For coasting or reverse gear, power flows only through the direct clutch.
^ All closed throttle 3-4 upshifts will occur at 25-28 mph, regardless of axle ratio.
^ All closed throttle 4-3 downshifts will occur at 25 mph, regardless of axle ratio.
^ No 3-4 upshift can be achieved, regardless of vehicle speed, if throttle opening is greater than 70% approximately.
OVERDRIVE DIAGNOSIS