RPM Question

[Hook]

Approximately how many RPM's should my L3240 be turning before engaging the PTO for a 6 foot bush hog. My tractor has 26.5 hp at the PTO.

 

[1970cs]

Go to about half throttle. The driveline/PTO shaft is it a shear bolt or slip clutch?

Pat

 

[rjcorazza]

Half throttle is about what I spin my mower up with (1500rpm). With my previous L3410 the clutch had to be used to put the pto in gear, so it could be feathered somewhat.
Current L4060 with electric pto (no clutch pedal) engages smoothly at 1500 also.


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[Hook]

Go to about half throttle. The driveline/PTO shaft is it a shear bolt or slip clutch?

Pat

Shear bolt. Thank you all for responding.

 

[lugbolt]

I asked Kubota about this a number of years back. They said anything with a hydraulic pto clutch would benefit from engaging the pto at a low speed, close to idle if possible, and then reducing the engine speed back to idle before disengaging. We were speaking of an M9540 at the time but the tech I spoke with mentioned that the same principles applied to anything with a hydraulic PTO clutch, which also includes the grand L's.

The loads places on the hydraulic clutch are lessened during the engagement and disengagement processes if the RPM is low both times. Not that the clutch is "weak" by any means, but if I can reduce stress on something, I try to as much as possible. The 9540 in question above had suffered a pto clutch holder failure where the pto brake actually broke the "tab" off of the clutch holder from disengaging the pto with it still being at speed. Common issue which Kubota has addressed, but it's not an inexpensive fix on those if a tractor owner has to pay for it. I don't imagine a grand L PTO clutch is cheap either.

 

[1970cs]

Shear bolt. Thank you all for responding.

Ok lower it till it's just above stall! You will have to experiment with the RPM's

The shear bolts don't take kindly to harsh engagements. The electro/hydaulic engagements are usually all or nothing. Or very little modulation/feather/cushioned start up.

Pat

 

[bearbait]

I asked Kubota about this a number of years back. They said anything with a hydraulic pto clutch would benefit from engaging the pto at a low speed, close to idle if possible, and then reducing the engine speed back to idle before disengaging. We were speaking of an M9540 at the time but the tech I spoke with mentioned that the same principles applied to anything with a hydraulic PTO clutch, which also includes the grand L's.

The loads places on the hydraulic clutch are lessened during the engagement and disengagement processes if the RPM is low both times. Not that the clutch is "weak" by any means, but if I can reduce stress on something, I try to as much as possible. The 9540 in question above had suffered a pto clutch holder failure where the pto brake actually broke the "tab" off of the clutch holder from disengaging the pto with it still being at speed. Common issue which Kubota has addressed, but it's not an inexpensive fix on those if a tractor owner has to pay for it. I don't imagine a grand L PTO clutch is cheap either.

Good advice, no need to have it above idle at startup or shut down

 

[dandeman]

if I can reduce stress on something, I try to as much as possible...

ditto.. same here...
This from experience from my Ford 4000 with live PTO driving a heavy duty built 6' bush hog. Although not a hydraulic drive, the PTO clutch on this tractor is a wet clutch pack in the transmission (i.e. expensive repair) and not something to abuse.

The inertia of the rotating mass in a heavy duty 6' bush hog can be enormous, and it makes sense to engage only at idle to minimize drive line shock loading and clutch slippage during engagement.

I even installed an external overrun clutch on the PTO shaft as the overrun torque (quite audible in the gear train noise, effect on engine rpm) when dropping the throttle speed is significant from the flywheel effect of the bush hog rotating mass. Also lowered the setting on the bush hog slip clutch.

Perhaps with some cheaper, lighter construction bush hogs this would not be so noticeable, but the used unit I bought decades ago is built like a tank..