Problems With The Ford AX4S Transmission: What You Need To Know
Posted by Regis on Monday, January 7th, 2013
The AX4S is a 4 speed trans-axle developed by Ford for front wheel drive vehicles. The AX4S comes from a family (in this order from oldest to news) of transmissions that includes the AXOD, AXOD-E, AX4S and the AX4N/4F50N. Although the first transmission in this family was introduced in 1989, the AX4S did not go into production until 1993. It was used in the Lincoln Continental, Ford Tarus, Sable and Windstar. It was discontinued after the 1993 model year and replaced by the AX4N/4F50N.
Although the AX4S is the third member in family of transmissions it still has its share of problems. You’d think after the third redesign the transmission would be problem-free, but unfortunately that’s not the case. Here are some of the more common problems with the AX4S and what to look for next time your customer brings one in with a problem.
The transmission hesitates to engaging at a stop. This points to a problem with the pump possibly. I have seen where a pump shaft sheared and caused this exact symptom.
The 2-1 down shift is harsh. The problem here is a defective solenoid. What is happening is that the shift solenoid is not mechanically deactivating. The spring portion of the valve is hanging and causing a very long downshift because it is so slow to return to the off position. Even though this problem is with an electric solenoid, I want to stress this is a mechanical failure. Disassemble the solenoid and see if you can determine what’s holding up the spring. It could be rust or debris that got into the solenoid. Use a fine grit emery cloth to remove any rust of small imperfections and see if that helps. Otherwise the solenoid with need to be replaced.
Fluid is leaking from somewhere on the transmission. Fluid can be coming from a number of different places. It could be a bad or over tightened pan gasket or the servo gasket on the side of the transmission. It could be a front or rear seal or the seal around the shift lever. The vent plug at the top of the transmission could be blocked, and when the fluid gets hot it expands and comes out the drain tube. I’ve even seen the cheap transmission lines that Ford uses on some of these transmissions rust and develop a pinhole leak.
The speedometer suddenly drops to zero while moving and then the transmission won’t shift. The most common cause of this problem is a malfunctioning VSS (Vehicle Speed Sensor). I would first remove the sensor and clean it with electronics cleaner. If that doesn’t fix the problem, I would replace the VSS with a new one.
Ford made a lot of these transmissions so sooner or later a customer is going to bring you one in for repairs. Hopefully, the above information will help you quickly diagnose the problem with your customer’s AX4S.