Up To Standards
- Author: Mike Weinberg, Contributing Editor
In 2002 Ford introduced a new four-door model of the venerable Explorer and its sister, the Mercury Mountaineer. The manual-transmission option for the new four-door model is a five-speed fully synchronized unit designated the M5R4 or M5OD-R4. The M5R1 transmission we all know and love has been replaced by a radical new design built by Mazda. This unit bears no resemblance to the M5R1.
The new model has a detachable bellhousing, a main case and extension housing, all made of aluminum. The mainshaft and countershaft are supported by tapered bearings with shims under the races to set endplay. All speeds are fully synchronized with helical-cut gears. The speed gears all run on needle bearings on the shafts. Gone is the removable shift cover, and all shift components are housed in the main case. Mercon ATF is the lubricant fill specified for the M5R4.
- 1st gear – 3.38-1
- 2nd gear – 2.06-1
- 3rd gear – 1.30-1
- 4th gear – 1.0-1
- 5th gear – 0.790-1
- Reverse – 3.70-1
The M5R4 represents one of the most-radical design changes in rear-wheel-drive manual transmissions. Traditionally, rear-wheel-drive stick units have been designed with 4th gear being the input shaft. The input was relatively short, with the drive gear mounted behind the input bearing and a pocket in the input to support the pilot journal of the mainshaft on a needle or tapered bearing. On the M5R1 unit the 3-4-synchronizer assembly is on the mainshaft directly behind the input gear. The 1-2 speed gears and synchronizer assembly and the 5th and reverse driven gears are on the mainshaft. The 5th and reverse speed gears and synchronizer are mounted on the countershaft.
The design of the new M5R4 locates the 5th gear as the first gear on the input shaft, followed by reverse, 1st, 2nd and 3rd gears, in that order. At the rear of the input shaft is the 3-4-synchronizer assembly. Fourth gear is part of the shortened output shaft or mainshaft. Mounted on the countershaft are the 5th and reverse synchronizer and speed gears and the 1-2 speed gears and synchronizer assembly. The input gear drives the 5th, 1st and 2nd gears and the reverse idler gear. We have included a parts illustration and power-flow charts to help you understand how this design works.
Three stirrup-shaped shift forks ride on shift rails and are positioned by three pairs of shift-fork lock plates that are bolted through the sides of the main case. There is a conventional detent and interlock system to give the driver shift feel and to prevent engaging two gears at once.
Study the power-flow diagrams and parts schematics in Figures 1 through 5, as the diagnostic routines will be very different on the M5R4 because of the unconventional gear placement. We are used to seeing the geartrain mounted from front to back as 4th, 3rd, 2nd and 1st. Here we have 5th, reverse, 1st, 2nd, 3rd and 4th. Studying the design, we see that the input shaft resembles the design found in a transaxle rather than that in a rear-wheel-drive truck transmission.
With this being the introduction year for this gearbox, it is too soon to judge the durability of this design, but time will tell. One thing I’ve learned in the decades I’ve spent in auto repair is that it is never dull and that change in vehicle and component design will never stop. This design may not start a trend, but we will learn to service and repair these units profitably because we are professionals.