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I just picked up this lifted 1979 F100 the other day. The speedometer was not working. The driven gear looks OK, but the drive gear teeth seem to be mushed (melted maybe?), so I was going to replace the drive gear. Because it's melted, it's hard to count the number of teeth, but it looks like it's 6. The truck is a four speed manual 4WD. The previous owner thinks it's a 360 or 390, he wasn't sure what the ratio was on the back end either, and I haven't had time to dig in an figure out either.
I looked on MAC's auto website but it shows a drive gear and several white driven gears for the 1979 F100. I'm guessing that they changed those to yellow due to the larger tires. I can find a yellow drive gear that is for Mustangs but that one has teeth on the inside while the grey one on MAC's is smooth.
Anyone have any suggestions on what drive gear I should order? Any hints on how to figure out whether I have a 360, 390 or something else?
I just picked up this lifted 1979* F100 the other day. The speedometer was not working. The driven gear looks OK, but the drive gear teeth seem to be mushed (melted maybe?), so I was going to replace the drive gear. Because it's melted, it's hard to count the number of teeth, but it looks like it's 6. The truck is a four speed manual 4WD.
The previous owner thinks it's a 360 or 390. No 360/390's after 1976. If it isa 1979, it could be a 302 (6 valve cover bolts), 351M or 400 (8 valve cover bolts).
He wasn't sure what the ratio was on the back end either, and I haven't had time to dig in an figure out either.
To get the correct speedometer DRIVE gear (located on the output shaft), the trans type, axle ratio and tire size are required.
Post the AXLE code stamped on the 2nd line-far right of the Warranty Plate, riveted to the left door face below the latch.
3 possible 4 speeds, need the TRANS code from the Warranty Plate, it's just before the AXLE code.
The nylon DRIVEN gears (16 thru 21 teeth) are the same: 1960 and later Passenger Cars & F100/350's, 1961 and later Econolines, 1966 and later Bronco's.
These gears are available from Ford and auto parts stores.
*Your "1979" has a 1973/77 grille frame and 1976/77 grille inserts.
F100 the other day. The speedometer was not working. The driven gear looks OK, but the drive gear teeth seem to be mushed (melted maybe?), so I was going to replace the drive gear. Because it's melted, it's hard to count the number of teeth, but it looks like it's 6. The truck is a four speed manual 4WD. 
