That would be a 351w engine, neither the 351C or 351M made it past 1980 and the cleveland was never installed in trucks anyway.
Shifting in and out of 4Hi can be done on the fly, just lock the hubs and pull the lever or press the button when you need it. Shifting into 4Low must always be done with the vehicle stopped and the transmission in neutral. DO NOT drive on clear pavement with 4wd locked in or drivetrain damage will result, snow covered roads and offroad is OK. Note it is safe to drive straight forward on clear pavement in 4wd but turning is where problems start, the rear wheels turn a shorter radius than the front and that creates binding, so don't do it. The manual transfercase shift mechanisms always seize up and forcing them to move will usually break something, if yours doesn't move freely dismantle and lubricate it.
Be sure to excersise the 4x4 monthly, lock in the hubs, no need to pull the shifter, just lock in the hubs and drive around a couple miles. This is to get everything turning in the front axle to lubricate the bearings, seals etc.
Check your tranny fluid while engine running and warmed up to operating temps*
Check the level ofcourse and color, and smell it. If it is abit dark, smells burnt, flush it as soon as possible! Flush and filter!
1990 Ford F250 4x4, ZF5, L/S 4.10, N/A 7.3L Diesel, 568,808km/377,497 miles, still on the original clutch!
1989 Ford F150 300-6, C6, 2.73, 152,000km/95,000 miles.
1987 Ford E350 26ft. Motorhome, N/A 6.9L Diesel, C6, 3.54, 289,000km/180,000 miles.
1985 Ford E350 Ext Van, 6.9L Diesel, C6, 4.11, 677,000km/425k miles
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