Questions regarding PTO's

[Jason Mills]

I am looking to understand PTO's better. I've never used one, or been around someone who has. Starting from zero practical and all but zero intellectual experience.


Specifically drivers side mounted PTO attached to the Spur gear transmission found in the early Power Wagons, and how they varied as the trucks progressed into the sweptline era.

Can PTO's found on the sweptline era that are mounted on the NP435 and NP540 transmission be used on ether drivers side or passenger side of the transmission?

The only information I have comes out of TM 9-8030 for the M-37. It states that the PTO operates at 40% of engine RPM.

Is that consistent with all PTO's for all year trucks (that they run at about 40% engine speed)?

What amount of torque can they transmit at 100% duty cycle?

Any and all suggestions, and input welcome.

[Desoto61]

The PTO can usually be mechanically bolted to either side of the transmission (assuming you have a PTO port on both sides), however you usually have to build the PTO to support this (the input gear may need to be reversed in the housing). Most can also be built to output forward or backward (or both with the right parts depending on the design).

Of course just because there are bolt holes doesn't mean it will go there. Lots going on on the passenger side of early Power Wagons/M37s and such where the driveshaft and transfer case levers all potentially sit in that same space.

Torque output of any gearbox will be based upon the gear ratio of the input vs output speeds. Don't know specifics for the boxes you reference but I imagine they stayed very similar as the winch that box connected to didn't really change much and that will be one of the limiting factors in speed and output.

[Jason Mills]

The PTO can usually be mechanically bolted to either side of the transmission (assuming you have a PTO port on both sides), however you usually have to build the PTO to support this (the input gear may need to be reversed in the housing). Most can also be built to output forward or backward (or both with the right parts depending on the design).

Of course just because there are bolt holes doesn't mean it will go there. Lots going on on the passenger side of early Power Wagons/M37s and such where the driveshaft and transfer case levers all potentially sit in that same space.

Torque output of any gearbox will be based upon the gear ratio of the input vs output speeds. Don't know specifics for the boxes you reference but I imagine they stayed very similar as the winch that box connected to didn't really change much and that will be one of the limiting factors in speed and output.

So different PTO gear assembly's can influence the speed of the output shaft, which has a bearing on the amount of torque one can put through them. Is that accurate? and some PTO's will turn at a higher percentage of the mainshaft speed? some will be slower, based upon what they were intended for. ..?

Yes I agree that the passenger side of the truck is busy.. I am interested only in using the drivers side PTO port...

I Have a PTO for a NP435, and one for a 540. I have not even thought to look and see if they are the same or different. Guess I should do that this W/End.

[Desoto61]

Torque through a gear set is simply the input torque multiplied by the gear ratio. Put in 1 lb. ft. of torque into a 2:1 gearset and you get 2 lb. ft. out, just at half the input speed, which is always the tradeoff.

If you go to the Chelsea-Parker web site there are a ton of different PTO designs and setups depending on what it was intended for. Pumps may want more speed than torque and have a lower reduction, while mechanical PTOs are usually the other way around, but again it would depend on what was being driven, how it's being driven, and at what speeds it can or will need to operate.

40% of engine speed means there's a 2.5:1 reduction somewhere between the engine crankshaft and the PTO output shaft. The question would be where that reduction happens. It could be all in the transmission or all in the PTO.

I've been trying to get a PTO set up for my truck but the input gear is no longer manufactured for the PTO I'd like to use which is reversible. I have another PTO for that trans that will work but it's non-reversible and runs at a certain speed ratio and I haven't yet figured if I can make it work. I had hoped I could change the input gears over from one case to the other, but the input gears are different between the two PTOs. While the tooth pattern is meant to go to the same transmission, the way it mounts and meshes with the PTO gearing is different. So even if the PTOs you have are the same, the input gears are probably different.

On the plus side if you are using it to drive an original winch then mimicking the factory setup (as close as you can) is probably your best bet since they were designed to work together.

There should be a data plate on the PTO with name and model number, go look those up to see what they are supposed to be. There were so many variations it's hard to know what you have otherwise. Then once you figure out which one best fits the device you want to drive your best bet is to find a local distributor for the PTO brand you have and go see them. There are lots of ways to set most PTOs up to support the side the PTO is mounted on and which direction it needs to drive. They will be able to do that if needed.

[Jason Mills]

Ah! I am beginning to understand. Thank you. I will go visit Chelsea-parker and do some reading.

[Desoto61]

Their older documentation seems to be pretty good if you know what series PTO you are dealing with, but that's not always clear.

Oh, and Muncie is the other big company that makes them as well. I think they've both changed hands in the past, but their web sites seem to still have decent info on the older setups. But I guess first issue would be to determine who made it!