NP435

New Process Gear's heavy-duty four-speed manual, built from 1962 and fitted by Ford, Dodge, GM, Jeep and International over a production run that outlasted most of the trucks it went into. In Ford's hands it is the four-speed of the F-100, F-150, F-250 and F-350 from 1966 to 1992, and of the full-size Bronco alongside them.

Like the GM SM465 it is a three-gear gearbox with a crawler in front of it. First is 6.68:1 and reverse is the same, and both are straight-cut and unsynchronised; second, third and fourth are helical and fully synchronised. So the shift into first while rolling will grind, and that is the design rather than a worn synchro. The pattern is a conventional H with reverse to the right and down.

Identify one by the top cover: eight bolts, aluminium, on a cast iron case. It weighs about 135 lb dry and measures a little over 17 inches overall.

The input shaft is what decides whether a used one will fit, and this is where most swaps go wrong. Ford's version is 1-1/16 inch and ten-spline with a 6-1/2 inch stick-out from the front face. Dodge's is not the same gearbox in this respect: early Dodge units to 1968 used a one-inch ten-spline shaft, and later ones a 23-spline shaft with an 8-3/8 inch stick-out. Measure the shaft and count the splines before buying — the cases look identical from three feet away.

On the name. New Process Gear became New Venture Gear in 1990, which is why an NP435 and an NV4500 can be described as coming from the same company and carry unrelated prefixes. Nothing changed inside the gearbox when the name did.