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Sherman Trans and PTO hp


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#1 DH1 ONLINE  

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Posted March 08, 2011 - 06:24 PM

OK guys here's a good question for ya.

1953 Ford Golden Jubilee with a Sherman combination step up, step down trans.

The tractor has a PTO hp rating of 32hp, 540 rpm without the Sherman.

The Sherman trans. changes the gear ratio between the engine and the tractor's trans.
You get 3 choices, step down, straight through(1to1) or step up.

So to get the PTO shaft to spin at 540 rpm the engine rpm changes.
Step down...........1000 Engine rpm = 540 PTO rpm and ?? PTO hp
Straight...............1500 Engine rpm = 540 PTO rpm and 32 PTO hp
Step down...........2200 Engine rpm = 540 PTO rpm and ?? PTO hp<<<

My question is HOW MANY PTO hp is there in step down with the PTO shaft turning 540 rpm? The engine is turning 2200rpm.

I have asked this question before on other forums and I don't get a number only generalizations.
This time I have more info see picture. I hope it shows clear enough.
shermco.jpg http://www.oldfordtractors.com/sherman/shermco.jpg

The reason I ask this question is the tractor is used for field grass cutting
1st gear travel speed is 2.68 mph and you can't slow down without slowing the PTO.
With a Sherman in step down the travel speed and PTO speed are the same but the engine is now turning 2200rpm instead of 1500rpm.
There has got to be more power there just in gear ratio along, also the engine probably makes more power at 2200 verses 1500. But how much???

A side note Ford made the 600s a few years after the Jubilee, basically the same tractor, same engine, some had the same 4sp trany, some had a 5 speed trany. Differences in engine to PTO rpm.
4sp 1500 engine rpm to 540 PTO and 32hp
5sp 1800 engine rpm to 540 PTO and 36hp

#2 Texas Deere and Horse OFFLINE  

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Posted March 08, 2011 - 07:11 PM

Doug, I will have to get back to you do that.:confuse::wallbanging:

#3 Alc ONLINE  

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Posted March 08, 2011 - 07:33 PM

Doug I have no clue but was wondering does your tractor have a separate pto shaft from the trans. ? Guess what I mean is does the if you keep the engine rpm the same does the PTO rpm's change with different gears ? My 3400 Ford uses 2 . Thanks Al

#4 DH1 ONLINE  

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Posted March 08, 2011 - 07:42 PM

Doug I have no clue but was wondering does your tractor have a separate pto shaft from the trans. ? Guess what I mean is does the if you keep the engine rpm the same does the PTO rpm's change with different gears ? My 3400 Ford uses 2 . Thanks Al


No it's not live pto. When the PTO is engaged it changes rpm as the engine does and the ground speed. 1st gear is the lowest gear and when you cut long heavy grass it's a bit to fast. Tractor does not have hi/low range and only 1 pto speed.

#5 Alc ONLINE  

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Posted March 08, 2011 - 08:05 PM

I thought that's how those worked , so no matter which step down your using the ground speed and pto will stay proportioning the same ? Anything less then 2.68 mph will drop your pto RPM 's ? Will that affect you mower ?

#6 MH81 ONLINE  

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Posted March 08, 2011 - 08:07 PM

Wow Doug,I always thought the Sherman unit had a pass thru for the PTO. Learned something new today. I have a friend that may have that answer. He's in Fla right now, should be back in another month, will ask him when he returns.

I see the ad says 37% increase in Hp due to increased RPM and Gearing. The other figure doesn't quite wash with that: 1.5 to 1 gearing in low, 1 to 1.5 in high. that would equate to a 50% gain or loss... I'm guessing the missing 13% is due to add'l gears & friction/etc. but that seems high percentage wise.

Edited by MH81, March 08, 2011 - 08:14 PM.


#7 DH1 ONLINE  

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Posted March 08, 2011 - 08:14 PM

I thought that's how those worked , so no matter which step down your using the ground speed and pto will stay proportioning the same ? Anything less then 2.68 mph will drop your pto RPM 's ? Will that affect you mower ?


Yes that's what this does ground speed and pto stay proportional the same and slower than 2.68mph drops pto rpms which slows down the mower.
My thinking was that if the engine is turning faster 2200 verses 1500 it would have more power, but how much more?

Let me rephrase the question.
How much more power do you think a 134cid OHV 4 cly. engine would have at 2200rpm verses 1500 rpm?
5% 20% 50%???

#8 DH1 ONLINE  

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Posted March 08, 2011 - 08:23 PM

I see the ad says 37% increase in Hp due to increased RPM and Gearing. The other figure doesn't quite wash with that: 1.5 to 1 gearing in low, 1 to 1.5 in high. that would equate to a 50% gain or loss... I'm guessing the missing 13% is due to add'l gears & friction/etc. but that seems high percentage wise.


That's my thinking 37% more, there will be loses, more parts turning, but 37% more power means the 32hp goes up to almost 44hp and that's a lot.

#9 MH81 ONLINE  

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Posted March 08, 2011 - 08:29 PM

My only concern here is that is WOT on a 60 yr old engine. 2200 was no problem when it was new, but now... I'd be a little concerned with running her all the way open like that for extended periods of time and working hard while doing it. Don't need a sight hole into the engine.

What size & what kind of mower?

#10 Alc ONLINE  

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Posted March 08, 2011 - 08:37 PM

OK , you need to find a old brochure that has shows the hp & torque curves right ?

#11 Gtractor ONLINE  

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Posted March 08, 2011 - 08:40 PM

I get what you are saying but I believe you would have to know the HP at the crankshaft, at each engine speed, and then run all the percentages of PTO speed to do the correct figuring. There are a lot of variables to consider.
I have many hours running a 9N with the two speed Sherman and it has more than it wants with a five foot brushcutter in direct drive. Overdrive is only good for a road gear or split speeds if using a non powered attachment. The overdrive does make the 3 point hydraulic lift motivate!

#12 DH1 ONLINE  

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Posted March 08, 2011 - 08:49 PM

My only concern here is that is WOT on a 60 yr old engine. 2200 was no problem when it was new, but now... I'd be a little concerned with running her all the way open like that for extended periods of time and working hard while doing it. Don't need a sight hole into the engine.


I hear you on that one, 2yr ago this engine was all done. Bought a master engine kit for it sleeves and all, got the so called "super power kit" which is 65thou larger bore with high compression pistons, checked and measured the crank and got all the right size bearings, mains+rods. Sent the head out and it came back like new, all new valves, milled and whatever else they did. Manifold broke when I took it off so I got a new one, this one is made for the 172 engine but fits the 134 that I have, universal type. Got a new carb for the 1962 172 engine on it and the exhaust is 2" vertical instead of the 134s 1 5/8". I used a universal reverse flow cherry bomb muffler, only cause it was on the shelve and cheap. Surprising how quiet it is. Has 12 volt system with alternator, spin on oil filter conversion and solid state points eliminator. Also put a foot throttle on it. It runs pretty good, I find when it hits 1800 the revs fly up to 2200.

#13 Alc ONLINE  

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Posted March 08, 2011 - 08:50 PM

Does this have what your looking for ?
http://digitalcommon...ractormuseumlit
  • DH1 said thank you

#14 Gtractor ONLINE  

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Posted March 08, 2011 - 08:51 PM

Another thing to consider is the torque will drop significantly by the time engine speed reaches 2200 rpm. On the flatheads of the 9N and 8Ns it would be way worse than the OHV 134s.

#15 DH1 ONLINE  

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Posted March 08, 2011 - 09:06 PM

What size & what kind of mower?

I want to get a 5 ft flail for it.




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