Ford 5R55N

Transmission general data

The 5-speed automatic transmission 5R55N (5R55W, 5R55S) was released in 2000 and found application in Ford Explorer and THUNDERBIRD. Besides Ford and Lincoln, it was installed on Mazda pickup trucks in Asia and on Jaguar S-type (for 2 years). In 2002, the problematic 5R55N was replaced by a new sub-modification 5R55W, and in 2003 the 5R55S was released with some updates. This transmission is installed on RWD and 4WD vehicles with quite powerful engines (from 3 up to 5 liters). In terms of design, this transmission belongs to the 4R44 - 4R55E family .

Technical issues and repair guidelines

The design of this transmission includes a forced electronic control of the torque converter lock-up. It complicates the system operation and makes it dependable on the ATF quality. The torque converter of the automatic transmission clogs the valve body quite rapidly and turns out to be the main reason of the valve body contamination and failure of the solenoids.

During the first years of operation, it is required to monitor possible leakages (quantity and quality of oil MerconV - 11.5 liters) and the filter condition. The 5R55N is very sensitive to contaminated ATF and the torque converter repair is the first in the list of rebuilding procedures.

The most common repair procedure is replacement of the filter and the pan gasket. There are 3 modifications of filters depending on the pan dimensions and year of manufacture.In addition to spare parts, it is frequently required to replace brake bands (Intermediate - O.Drive). One more constructive problem is the failure of the band locking plate caused by sidesway and vibrations. They are replaced together with the servo piston.In many cases, sensors of the output\input shaft speed (VSS\ISS) also get replaced.

In most cases, friction components of the Forward package get burnt, but specialists replace not only a full kit of friction discs, but also steel discs and the bearing disc of this package.The pump valve is the most vulnerable element in the pump. Sticking of the valve leads to delays in gear shifting or even to the lack of the pull-rod at growing engine revs.

The valve body is repaired quite often, therefore Sonnax released many repair kits for rebuilding of these transmissions. This problem is common for all valve bodies produced in the early 2000s, in which the torque converter locking was performed too early and accompanied by strong slippage. It is complicated by the fact that drivers in these situations too often use aggressive accelerations and too rarely changed ATF and the torque converter friction elements.

It is recommended to install additional cooling radiator on “old” cars, which went through the ATF overheating and burning of friction elements.