Manual Transmission/Transaxle: Description and Operation

Manual Transmission
The S6-650 and the M6HD transmissions are -speed synchronized units. The ZF 6-speed has the following features:
^ An integral clutch housing
^ An aluminum main case, extension housing and intermediate housing
^ The mainshaft has two tapered roller bearings. Mainshaft end play is controlled by a selective shim located under the bearing cup
^ The countershaft has two tapered roller bearings. The countershaft end play is controlled by a selective shim located under the bearing cup
^ The countershaft is serviced as an assembly
^ Synchronized in all gears
^ All gears are helical
^ All gears, including reverse, turn on needle roller bearings
^ Single-piece shift forks with moly coated pads
^ Internal oil pump, driven by the countershaft, to supply transmission fluid to an external cooler
^ Provisions for mounting a power take-off unit
^ A reverse idler gear that does not need to be removed during disassembly
^ The mainshaft and countershaft are assembled under preload. If the ZF transmission is disassembled, a preload measurement must be taken

The S6-650 and the M6HD have six forward speeds that feature a LOW gear for take-off under heavy loads and a OVERDRIVE gear for highway driving conditions. The gear ratios are as follows:
^ Low 5.79:1
^ First 3.30:1
^ Second 2.10:1
^ Third 1.31:1
^ Fourth 1.00:1
^ Overdrive 0.72:1
^ Reverse 5.23:1

Transmission Identification
All ZF transmissions are identified by the model and serial number. This information is on the transmission identification tag and affixed to the transmission case. Do not remove or destroy the transmission identification tag.

Part 1:

Part 2:

Part 3:

Transmission Internal Components - Disassembled View

Part 1:

Part 2:

Part 3:

Transmission Internal Components-Disassembled View

Part 1:

Part 2:

Transmission Shift Components - Disassembled View

Lubrication

CAUTION: Additives and friction modifiers are not recommended for use in ZF transmissions.

ZF transmissions are designed so that the internal parts operate in an oil bath circulated by the motion of the gears and shafts. All parts are amply lubricated if these procedures are followed:
^ Maintain the correct fluid level by inspecting it regularly.
^ Change the fluid regularly. Refer to the owners literature for the recommended intervals.
^ Use MERCON Multi-Purpose Automatic Transmission Fluid XT-2-QDX or equivalent meeting Ford specification MERCON.

High operating temperatures increase the lubricant's rate of oxidation and shorten its effective life. When the average operating temperature is high, the transmission may require more frequent fluid changes or external cooling. External oil coolers are used to reduce high operating temperatures. The following conditions in any combination can cause high operating temperatures:
^ Operating consistently at slow speeds.
^ High ambient temperatures.
^ Restricted air flow around the transmission.
^ Exhaust system too close to the transmission.