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Regarding the 540, 541, 542 transmissions:
Consider the direction you pull the stock 4-speed to get it into direct (4th). That is where direct is in the NP 540-series 5-speed. That is where direct will always be on that transmission, whether it is 5th direct or 5th overdrive. The difference in the direct and the OD transmissions is in the ratio you have with the lever pushed to that forward position.
Shift the transmission into direct; on that trans it will involve a pull of the lever’s knob toward the rear bumper of the truck. You can verify where direct is simply by turning the input shaft and watch the output shaft. The two shafts should turn at the same speed, indicating the direct ratio of 1:1.
Make index marks on the input shaft and the output shaft with a felt tip pen. Shift the lever in to the position forward from direct. Turn the input shaft one turn, count the turns at the output shaft.
If the output shaft turns more than one revolution, you have an OD trans. If it turns less than one turn, it is a direct.
Consider the direction you pull the stock 4-speed to get it into direct (4th). That is where direct is in the NP 540-series 5-speed. That is where direct will always be on that transmission, whether it is 5th direct or 5th overdrive. The difference in the direct and the OD transmissions is in the ratio you have with the lever pushed to that forward position.
Shift the transmission into direct; on that trans it will involve a pull of the lever’s knob toward the rear bumper of the truck. You can verify where direct is simply by turning the input shaft and watch the output shaft. The two shafts should turn at the same speed, indicating the direct ratio of 1:1.
Make index marks on the input shaft and the output shaft with a felt tip pen. Shift the lever in to the position forward from direct. Turn the input shaft one turn, count the turns at the output shaft.
If the output shaft turns more than one revolution, you have an OD trans. If it turns less than one turn, it is a direct.