ZF S5-42, S5-47 Fluid Replacement Procedures

How to Replace the Fluid in a ZF 5 Speed Manual Transmission

The ZF S5-42 and later S5-47 five speed manual transmissions were used in Ford diesel pickups from 1987 to 1997. Few 6.9L IDI engines were made available with the ZF 5 speed, but it was standard issue for the 7.3L IDI and 7.3L Power Stroke during these model years.

Applicable Model Years: 1987 to 1991 Ford F-Series
Applicable Transmissions: ZF 5 speed S5-42 & S5-47
ZF S5-42/S5-47 Fluid Spec: Motorcraft MERCON V synthetic ATF (replaces defunct MERCON spec)
ZF S5-42/S5-47 Fluid Capacity: 3.38 quarts

The ZF 5 speed transmissions are known to be rugged and relatively strong with the only major concern being synchronizer wear. Synchro wear occurs naturally through normal use but can be expedited by improper operation and/or abuse (slamming gears, power shifting, not using the clutch properly, harsh downshifts at high RPM, etc). Both the ZF S5-42 and later S5-47 transmissions require full synthetic MERCON V automatic transmission fluid for lubrication (MERCON V replaces the original MERCON spec, which is now defunct and no longer produced by Ford). Failure to use the proper fluid will result in reduced shift quality and premature wear. Ford recommends replacing the transmission fluid at 60,000 mile intervals, however you may consider 30,000 mile service intervals if you tow frequently; the fluid in manual transmissions tends to reach very high temperatures and the ATF will degrade more rapidly under high load conditions.

If you have not already performed the Heim Joint Mod for 1988 - 1997 Ford trucks, we highly recommend you consider the upgrade. It completely removes and eliminates the problematic plastic bushing found in the eye of the clutch master cylinder pushrod. This is a permanent, maintenance free fix for an extremely common problem associated with the ZF 5 speed manual transmission.

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ZF 5 speed transmission fluid

• The ZF 5 speed manual transmission calls for 3.38 quarts (3.2 liters) of synthetic MERCON ATF (Ford part number E6AZ-19582-B) or Castrol TRANSMAX-S ATF. Yes, this manual transmission requires the use of automatic transmission fluid due to its tight design tolerances. Thick gear oil is not compatible with the transmission and will cause poor performance, premature wear, and/or driveability issues.

ZF 5 speed drain and fill plug locations

• Park the vehicle on level ground before attempting to change the fluid.

• Locate the transmission's drain plug and fill plug (see image at left if in question). Place a drain pan beneath the transmission and remove the drain plug and then fluid fill plug using a 7/8" wrench.

• Once the fluid has drained completely, reinstall the drain plug.

Filling the transmission with fluid

• Use a fluid transfer pump to fill the transmission with fresh ATF. The correct fluid level is up to the fill plug hole - when the transmission has reached the correct fluid level, ATF will begin to run out of the fill plug opening. At this time, remove the hose for your transfer pump and reinstall the drain plug.

Amsoil synthetic ATF for ZF 5 speed manual transmission

• We've chosen to use Amsoil's Signature Series multi-vehicle ATF for this transmission. This high quality fluid gave us smoother shifts and the peace-of-mind that our gear box is protected by one of the most renowned names in the lubrication industry.