Independent PTO drive

Texasmark1

Well-known Member
I purchased this 3910 recently and today I'm replacing the starter safety switch. I whipped out the I & T #43 and looked at the process. OK fine.

My curiosity has existed for a long time and today, while in the area of the tranny, it got me to looking at just how does a gear driven "Independent PTO"
get driven?

Looking at the tranny exploded view it's a no brainer looking at the dual shafts and all that allows the function to happen. The problem arises with the
drive mechanism.

Looking at the exploded views of the clutch and tranny, I see one primary shaft coming out the front of the tranny with a spline that fits into the splined
hub of the clutch disc.....one shaft connecting the disc. No other connection point that I can see for the PTO drive. Looking at the front end of the
tranny, you see how the dual shafts are hooked together and some where in there is the sliding sleeved spline that engages the output PTO shaft when
you move the PTO lever.

When the pressure plate is compressed, like when clutching to shift gears, the disc is separated from the engine's flywheel....ok fine.

The kicker: That being the case, with only one input shaft, how does the PTO get driven when the clutch pedal is depressed?

Something to do with your morning coffee. Wink!

Thanks,
Mark
 
Two input shafts: one INSIDE the other, and slightly longer. One engages splines in the clutch hub, the other engages splines on a hub that's riveted to the pressure plate. And in the back end, the pto lever atcuates a hydraulic clutch fir the pto, rather than a sliding sleeve.
 
What Fordfarmer said... plus that inner shaft also drives the hydraulic pump for the 3 point lift, and that pump is actually two pumps in one housing, the main larger pump for the lift and a smaller pump section on the back side that is what powers the hydraulics for the PTO clutch and brake.
 
Actually the outer shaft, on a 3-cylinder. It's the inner
shaft on 4- cylinder (and I would assume on 6-
cylinder) models.
 
(quoted from post at 09:42:30 06/19/18) Actually the outer shaft, on a 3-cylinder. It's the inner
shaft on 4- cylinder (and I would assume on 6-
cylinder) models.

I don't think that's possible. How could the outer shaft go all the way to the coupler on the flywheel and still allow the inner shaft to interface with the splines on the clutch disk?
 
The outer shaft (pto input) is the shorter of the two.
The pto hub is riveted to the rear side of the
pressure plate, so it extends farther back into the
bellhousing. Luke and I were just looking at this on
his 4000 a couple days ago. His 4000 is still split, as
we have to get a new pressure plate before we put it
back together - it has worn splines on the pto hub.
 
Thanks for hitting on this. I can see where there is a collar/pipe/sleeve type thing that is/appears to be splined or geared so as to connect to a power source. On terminology Mr. Farmer, I'm confused about what you are talking about.....help me if you will.

I know the flywheel is attached to the crankshaft.
The Pressure plate is mounted to the flywheel.
The clutch disc sits between the two and with the springs of the pressure plate being depressed via the "throwout" (clutch release) bearing the clutch pedal activates the release.

I can see the raised area on the tranny side of the clutch disc. Assume that the tranny input shaft fits there as is usually the case with clutch operated systems.
I don't see where the collar/sleve connects and don't understand your terminology.

Did you say that it connects to the rear of the disc., or does it connect to the rear of the crank shaft/flywheel via a splined adapater bolted to the flywheel.....continuous engagement as long as the tranny case is bolted to the engine block. I can understand that if it does.

Then, taking what Sean said about "how could that be possible......." if the shaft actually runs the hyd and PTO pumps and sticks into the rear of the crankshaft/flywheel, with no connection to the clutch assy, I can see how you could have the pumps pumping as long as the engine was rotating.

Then if the transmission were driven by the outside collar/sleeve hootus that splines into the adapter thing on the clutch disc, I can see how you can have the clutch control the tranny input power.

Am I getting the idea?

Thanks,
Mark
 
I'm not sure if I'm following this thread exactly.
Here's a couple of photos.
The inner and outer input shafts are the same on an IPTO and LPTO tractor.
The difference is in the pressure plates.
Here's a photo of the pp on a 4000 with Ipto.
Note how the splined hub that drives the pto (and hyd pump) is riveted directly to the pp.
a270923.jpg

a270924.jpg
 
The pto/hydraulic pump input shaft is driven by a splined hub riveted to the pressure plate, which is bolted to the flywheel... so continuous drive, whenever the engine is running. The transmission input shaft is longer, reaching farther ahead, to the splined hub of the clutch disk, allowing power to be interrupted by stepping on the clutch pedal.
This is a lot easier to understand if you have one split and right there to look at, as opposed to written, verbal, or drawn descriptions... for me, anyway.
 
Well that's the connection.

It is in fact the center shaft that goes to the disc and drives the tranny just like in most all engine transmission drive applications. Since the PP is bolted to the flywheel, the outer, hollow shaft is connected to it via the spline per your picture (which doesn't exist on normal manual transmission hookups, and as long as the PP is turning, aka the flywheel is turning, aka the engine is running, the outer (hollow) shaft turns. Makes perfect sense.

Thanks guys for clearing this up for me.

The last circle in your top picture is the throw out bearing which releases the PP from the clutch disc (like all clutch release designs) but not from the flywheel keeping the outer shaft turning while the transmission input shaft isn't.

Thanks for your time.

Surely somebody else on this forum has wondered about this over the years. Now WE know.
 
Correct. The PTO and pump drive is through the bottom transmission shaft on 3 cylinder models and through the top transmission shaft on 4 and 6 cylinder models.
 
I have, good post on this. I've looked over the OEM shop manual and they cover it well, but not the easiest thing to understand.
 

mvphoto18536.jpg

I'll try adding a picture, too. This (if it shows) is the flywheel, clutch disk, and pressure plate from Luke's 4000, looking at it from the rear. You can see the two sets of splines.
 
Perfect. I'm going to copy this picture and Dog's and put them in my manual for future reference if needed. I appreciate you guys jumping on this. It's been fun for me, hopefully for you guys too.

I don't know how you guys fix things but I try to remember that the building is built one brick at a time and each brick has a job. If you understand that, and I make it a point to do so, then when something breaks, it's easy to see which brick is out of place for your smoking gun.
 
Off topic, slightly: You said Luke's 4000....you currently working in this area on his tractor? In your picture am I noticing pretty good wear marks on the teeth which drive the pumps? I had a 4 cyl 4000 SOS years ago and it too was driven by a clutch disc between the flywheel and the PP but the PP remained pressed against the disc always (no clutch pedal perse....an inching pedal which interrupted hydraulic fluid pressure).

My disc spline was worn like what I think I see here and replaced it as a good measure. Tranny input shaft wasn't damaged, some wear marks, but not damaged. Time for a new PP assy or can those be repaired?
 
The S-O-S has a clutch, it is called a torque limiting clutch (TLC) and it is always engaged with no way for the operator to disengage it. It is similar to a "slip clutch" used on the PTO shaft of some PTO driven implements like rotary mowers and roto-tillers. The TLC is designed to slip when more than a certain amount of torque is applied so as not to damage things like the splines on the transmission input shaft and the coupler in the middle of the torque limiting clutch.

It is my suspicion that the TLC sometimes gets "stuck" via rust and/or humidity and dirt contamination and doesn't slip when it is supposed to, and that is what causes the damage to the splines.
 
Yes, a new PP will be ordered next time we go to our dealer. We have the engine pretty much back together after a full rebuild. This is a long-term project Luke and I are doing together as he earns the money for it. He was a little sick last week when we picked up the injector pump and injectors and the bill was about $750.
 
Okayeeeee. When I saw it I just assumed it was an easy way for Ford to connect the SOS to the engine with minimal odd parts. Makes sense that at
some point the disc could slip with enough pressure applied.
 
I can understand that. Many years ago we had a noted pump rebuilder in the area but like the SOS mechanic....time passes and so do folks. The International OTR/Farm equipment dealer had a pump/injector "lab" on site. Never used them but they seemed to be up to speed on what it took to get the job done.
 
"It is is my suspicion that the TLC
sometimes gets "stuck" via rust and/or
humidity and dirt contamination and doesn't
slip when it is supposed to, and that is
what causes the damage to the splines."

Well that and the bloody hammering the SOS
does when it shifts.
 
(quoted from post at 17:06:11 06/20/18) "It is is my suspicion that the TLC
sometimes gets "stuck" via rust and/or
humidity and dirt contamination and doesn't
slip when it is supposed to, and that is
what causes the damage to the splines."

Well that and the bloody hammering the SOS
does when it shifts.

If the TLC slipped properly when the transmission does a hard shift then I don't think the splines would get damaged.
 
Now that I am aware of a second use of the connection method Ford chose, on slipping or not, I'd compare it to a slip clutch on a PTO driven
implement.....if you don't do regular maintenance (of some sort) to the surfaces, it won't slip when you need it. I see the "slip" function on a 50 year old
tractor that has never been split a "pipe dream" on the part of the designer.
 
(quoted from post at 08:46:33 06/22/18) Now that I am aware of a second use of the connection method Ford chose, on slipping or not, I'd compare it to a slip clutch on a PTO driven
implement.....if you don't do regular maintenance (of some sort) to the surfaces, it won't slip when you need it. I see the "slip" function on a 50 year old
tractor that has never been split a "pipe dream" on the part of the designer.

I see a 50 year old tractor that has never been split as a pipe dream as well. But I guess it could happen with a hobby farm where the tractor only gets a few hours a year and regular fluid and filter changes. But there's usually something that needs a split to work on after 20 or 30 years no matter how few hours and how well maintained they are. Seals eventually fail, etc.
 

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