Entropy455
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Here’s some PTO information, for the M939 series trucks. Note: I’m posting this information because it was difficult to find, and it might be useful to others looking to convert their truck over to hydraulics. Please let me know if I’ve made any errors below.
The M939 series trucks utilize a MT-654CR Allison transmission. The transmission’s PTO drive gear (piece 11, of figure 187,of TM9-2320-272-24P-1) is a 64-tooth, 6” diametrical pitch, 20-degree pressure angle, straight-cut (non-helix), full-involute spur gear. The gear is downstream of the torque converter, thus it is powered whenever the engine is on, across all 5 forward gears, including neutral and reverse. Due to fluid-coupling within the converter, the transmission’s PTO gear turns at approximately 80% of crankshaft speed at low engine rpm, and approximately 1:1 at higher rpm.
Regardless of which PTO brand you select (stock or aftermarket) the input gear on the PTO itself must be a 6” diametrical pitch, 20-degree pressure angle, straight-cut (non-helix), involute spur gear.
The stock 5-ton PTO uses a 25-tooth input gear (piece 20, of figure 530, of TM9-2320-272-24P-2). The other two gears (piece 21 and piece 23, of figure 530, of TM9-2320-272-24P-2), combine for an overall PTO gearing of about 1.236:1 (overdrive with respect to crankshaft rpm). The Muncie TG6S series PTO, requires a U60 input gear for use with the MT-654CR Allison transmission, which is a 24-tooth gear. The TG6S-U6004 gears combine for an overall PTO gearing of about 0.963:1 (reduction with respect to crankshaft rpm). The TG6S-U6005 gears combine for an overall PTO gearing of about 1.255:1 (overdrive with respect to crankshaft rpm – which is similar to the stock 5-ton PTO).
For the purpose of sizing the hydraulic pump, assume the transmission PTO drive gear (piece 11, of figure 187, of TM9-2320-272-24P-1) is turning at 1000 rpm. This is a reasonable throttle setting for a PTO hydraulic application. Ensure your pump is safe to operate at the maximum engine rpm (max pump speed is 2100 rpm, times the PTO overall gear ratio).
The M939 series trucks utilize a MT-654CR Allison transmission. The transmission’s PTO drive gear (piece 11, of figure 187,of TM9-2320-272-24P-1) is a 64-tooth, 6” diametrical pitch, 20-degree pressure angle, straight-cut (non-helix), full-involute spur gear. The gear is downstream of the torque converter, thus it is powered whenever the engine is on, across all 5 forward gears, including neutral and reverse. Due to fluid-coupling within the converter, the transmission’s PTO gear turns at approximately 80% of crankshaft speed at low engine rpm, and approximately 1:1 at higher rpm.
Regardless of which PTO brand you select (stock or aftermarket) the input gear on the PTO itself must be a 6” diametrical pitch, 20-degree pressure angle, straight-cut (non-helix), involute spur gear.
The stock 5-ton PTO uses a 25-tooth input gear (piece 20, of figure 530, of TM9-2320-272-24P-2). The other two gears (piece 21 and piece 23, of figure 530, of TM9-2320-272-24P-2), combine for an overall PTO gearing of about 1.236:1 (overdrive with respect to crankshaft rpm). The Muncie TG6S series PTO, requires a U60 input gear for use with the MT-654CR Allison transmission, which is a 24-tooth gear. The TG6S-U6004 gears combine for an overall PTO gearing of about 0.963:1 (reduction with respect to crankshaft rpm). The TG6S-U6005 gears combine for an overall PTO gearing of about 1.255:1 (overdrive with respect to crankshaft rpm – which is similar to the stock 5-ton PTO).
For the purpose of sizing the hydraulic pump, assume the transmission PTO drive gear (piece 11, of figure 187, of TM9-2320-272-24P-1) is turning at 1000 rpm. This is a reasonable throttle setting for a PTO hydraulic application. Ensure your pump is safe to operate at the maximum engine rpm (max pump speed is 2100 rpm, times the PTO overall gear ratio).
