A/T - Chattering/Bucking On Slow Cornering
January, 1994Technical Bulletin # 202
^ Transmission: Subaru 4 speed with 4WD
^ Subject: Chattering/binding in corners
^ Application: Subaru
Subaru Automatic 4 speed with 4WD
Slow speed sharp corner chattering/binding
The Subaru automatic four speed with 4WD uses a computer to control shifting, pressure rise, the torque converter clutch, and the transfer clutch. A malfunction of the transfer clutch can result in a condition called "tight-corner braking", which is felt as a chatter or bucking while turning a corner slowly,
Inputs to the computer which may affect the operation of the transfer clutch are the VSS, TPS, inhibitor switch and manual switch. The transfer clutch is controlled by duty solenoid C. At 95% on time, the transfer clutch is released and at 25% on time, the clutch is applied. Fail-safe or loss of power to the solenoid will result in full time 4WD.
The following steps should be used to isolate the problem.
Step 1 Check for trouble codes: Trouble code retrieval procedures vary from model to model and year to year. Refer to the factory manual.
Step 2 Turn the transfer clutch off: This can be done by inserting the spare 15 amp fuse (or any 15 amp blade-type fuse) into the FWD switch (Figure 1).
If the tight-corner braking condition remains, check the transfer clutch pressure. When checking the transfer clutch pressure you should also check the voltage to duty solenoid C. This can be done by probing the wire to pin # 11 (Figure 2) with a voltmeter (dc volts).
With the fuse inserted, voltage on pin # 11 (key on, engine running), should be 8-14 v. Pressure should be 0 psi. With the fuse removed, voltage and pressure should vary with throttle opening. When the voltage is high, pressure should be low. When the voltage is low, pressure should be high. The chart shows pressure readings for the transfer clutch pressure tap (Figure 4).
^ If the voltage responds with throttle opening and pressure does not, then the solenoid may be defective or the transfer clutch valve may be stuck.
^ If voltage does not respond, then the circuit to the solenoid or the TCU would be the suspect.
^ if voltage and pressure respond to throttle opening, the transfer clutch assembly may be damaged (clutches locked on).