Rotary cutter thumps when PTO turned off

[JCCinOhio]

Never used a rotary cutter before.. Bought a used rc2048 for my JD2305. Got it all cleaned and lubed up and gave it a short test (didn't cut anything). Didn't sound too bad starting up or running, but when I turned it off there was quite a 'thump'. As it says in the manual, I lowered the speed to idle first before pushing in the PTO knob to turn the cutter off. Is a thump normal? There's a lot of momentum in the blades and I'm guessing the whole rotary part comes to a complete stop at once.

Would shutting off the tractor be a gentler way to bring the blades to a halt?

Don't suppose it's a good idea to try to use the PTO selector to change to front PTO when the rear is engaged? That would let it free spin to a stop.

I understand the safety issues in the two above statements....

 

[seville009]

Thumping and bumping and shaking is all normal for these. You can always give it a good look over when its off to see if you see any evidence of something else, but my guess is that it is fine.

if there was something wrong with the blades, i'd think you'd notice it while you were actually cutting.

 

[ptsg]

Never used a rotary cutter before.. Bought a used rc2048 for my JD2305. Got it all cleaned and lubed up and gave it a short test (didn't cut anything). Didn't sound too bad starting up or running, but when I turned it off there was quite a 'thump'. As it says in the manual, I lowered the speed to idle first before pushing in the PTO knob to turn the cutter off. Is a thump normal? There's a lot of momentum in the blades and I'm guessing the whole rotary part comes to a complete stop at once.

Would shutting off the tractor be a gentler way to bring the blades to a halt?

Don't suppose it's a good idea to try to use the PTO selector to change to front PTO when the rear is engaged? That would let it free spin to a stop.

I understand the safety issues in the two above statements....

Your tractor, like mine, uses a PTO clutch pack for the PTO engagement which has a spring actuated brake. With the PTO on, the hydraulic pressure clamps the discs and releases the brake. Once you turn it OFF, there is no hydraulic pressure and the spring brake actuates.

What you're hearing is just the brake stopping a high inertia implement.

My tractor has no mid PTO, just rear PTO with 540 - Neutral - 540E. Sometimes I use that trick of moving the PTO lever to Neutral and let the mower coast to a stop. Kinda saves the PTO brake a little bit I guess. If you get the timing just right between dropping the RPMs and gently moving the lever, it will come right out of gear with very little effort or damage to the shift fork.

 

[JethroB]

Maybe the thump was a blade banging into or on to the top of the stump jumper pan. If the mower is vibrating more after a restart one of the blades is likely hung up. I get that occasionally, raising and lowering the RPM’s a few times will usually break it free.

 

[hosspuller]

Only a single thump ? likely the driveline backlash going from driving to braking. I get a thump when starting my cutter. No PTO brake so it spools down slowly and evenly.

 

[CobyRupert]

Why do tractor manufactures put a brake on the PTO shaft? That’s just asking for trouble. Both when hooking up the pto and turning it off.

Sounds like an overrunning clutch on the pto shaft would be a solution. Just like the days of non-live pto tractors, when they were needed to prevent pushing in the clutch and having the mower’s momentum continues to drive the tractor’s wheels through the pto / transmission with sometimes disastrous results.
Finally, non live pto’s gave us a built in overrunning capabilities. Now, they put brakes on PTO’s. Why?
70 years later and we still need the overrunning clutch pto’s .

 

[LouNY]

PTO brakes work well on many implements. Many of the larger pto implements will have a built in overrunning clutch on
high inertia loads.
Or as has been mentioned install an over running clutch it can be combined with a slip clutch.
for the smaller tractors;

and if needed;

 

[Jerry/MT]

Your tractor, like mine, uses a PTO clutch pack for the PTO engagement which has a spring actuated brake. With the PTO on, the hydraulic pressure clamps the discs and releases the brake. Once you turn it OFF, there is no hydraulic pressure and the spring brake actuates.

What you're hearing is just the brake stopping a high inertia implement.

My tractor has no mid PTO, just rear PTO with 540 - Neutral - 540E. Sometimes I use that trick of moving the PTO lever to Neutral and let the mower coast to a stop. Kinda saves the PTO brake a little bit I guess. If you get the timing just right between dropping the RPMs and gently moving the lever, it will come right out of gear with very little effort or damage to the shift fork.

+1
The other thing that happens is that the blades tend to "fold" under the stump jumper when the pto shaft stops turning abruptly.. When you start up, those blades "unfold" usually with a bang.

I have an independent pto and my cutter has a slip clutch. In order to keep the rotary inertia of the cutter from wearing out the clutch pack on the internal pto drive, I installed an over-running clutch to the pto shaft. I slow the rpm s down and then disconnect the pto and the as the cutter slows down the over running clutch disconnects the cutter drive shaft from the pto shaft without loading up the pto clutch.

 

[hornett22]

Make sure your gearbox mounting bolts are tight

 

[2manyrocks]

I was thinking along the same lines to make sure the blade bolts are tight and the mounting plate for the blades is also tightened properly.