Over-running Clutch For PTO Inside The Tranny?

[npalen]

I use my Mahindra 3015 (30 HP wi hydrostat) quite a bit for roto-tilling and normally use the tractor clutch when engaging the mechanical PTO. I don't use the clutch for dis-engaging the PTO, however, but rather just move the PTO lever to the off position. The other day, for some reason, I pushed in the clutch to stop the tiller, and noticed a weird clunking noise in the transmission that sounded like some kind of over-running clutch as the tiller was coasting to a stop.

So did some testing by turning the roto-tiller manually with the engine off but the PTO engaged and was able to duplicate the noise.

So I ordered a PDF of the service manual for the tractor and sure enough, after some searching, found the section showing an over-running clutch inside the Mahindra transmission.

I've heard of over-running clutches in the external PTO driveline used on rotary mowers, for example, so that tractors with non-live PTO's would not be over driven while the PTO is coasting to a stop. An internal over-running clutch in the tractor, however, is a first for me and wondering what you guys might know about this and whether it is common especially in a hydrostat tractor.

TractorData.com Mahindra 3015 tractor information

www.tractordata.com

 

[claggstractors]

I use my Mahindra 3015 (30 HP wi hydrostat) quite a bit for roto-tilling and normally use the tractor clutch when engaging the mechanical PTO. I don't use the clutch for dis-engaging the PTO, however, but rather just move the PTO lever to the off position. The other day, for some reason, I pushed in the clutch to stop the tiller, and noticed a weird clunking noise in the transmission that sounded like some kind of over-running clutch as the tiller was coasting to a stop.

So did some testing by turning the roto-tiller manually with the engine off but the PTO engaged and was able to duplicate the noise.

So I ordered a PDF of the service manual for the tractor and sure enough, after some searching, found the section showing an over-running clutch inside the Mahindra transmission.

I've heard of over-running clutches in the external PTO driveline used on rotary mowers, for example, so that tractors with non-live PTO's would not be over driven while the PTO is coasting to a stop. An internal over-running clutch in the tractor, however, is a first for me and wondering what you guys might know about this and whether it is common especially in a hydrostat tractor.

Very common in modern tractors. That would be the "dog ear" style, which is noisier but more durable.

 

[npalen]

So what exactly is the purpose of the over-running clutch in modern tractors with live PTO?

 

[claggstractors]

Good question. Only reason I can figure is to make it shift out of gear while still turning without "scratching" the gears. I know on the Branson's before independent PTO came out it would allow you to up and down shift the PTO while the implement was still turning. Maybe a hold over on that Mitsubishi from the Japanese market. Would probably have a multi speed PTO over there.

 

[CalG]

Without an over running clutch, any PTO driven attachment with inertia will DRIVE the tractor even if the clutch is pressed or the transmission is in neutral. Snow blowers might be a useful example. I can tell you, when you are hoping to slow and stop forward progress by declutching around building and such, and the tractor just keeps driving forward , it's an unsettling sensation.

My old E27n Fordson is like that. Scary .. I put an over running clutch on the PTO stub after the first scare.

The Kubota B7200 has an internal over run clutch. That's a pretty old design. The Hurlimann has a two stage clutch, so no issues there. It also has a ground speed gearing for the PTO output which would send power to the wheels from any spinning implement.

If fitted with a hydrostatic transmission, I can see a BIG surprise to the operator if the tractor is driven along by inertia with the go pedal in neutral ... Whee Haa!

 

[npalen]

This is all news to me especially on tractors with a two stage clutch. I thought an independent PTO was just that, seperate from the ground drive. Is there a difference between electric PTO clutch and mechanical clutch when it comes to the "overdrive issue"? I thought for sure that a hydrostat would be immune especially when the pedal(s) are "centered".

 

[TerryR]

Without an over running clutch, any PTO driven attachment with inertia will DRIVE the tractor even if the clutch is pressed or the transmission is in neutral.

Not on any modern tractor with independent PTO.

 

[npalen]

With curiosity aroused, I checked the WSM for my Kubota B9200 HST and found this:

 

[CobyRupert]

So…does this mean you can’t start a modern compact tractor by rotating the PTO shaft?
Can’t find the video anymore of a guy who coiled a fire hose around the rotary mower PTO shaft and then connected it to the family car and had his wife drive away. The tractor started right up. I thought it was a pretty slick way to “pull start” a hydro.

Does this also mean you can’t turn your PTO on (with the engine off) to “lock” the PTO in place. I do this and manually turn the rotary mower blades to confirm that the mower’s slip clutch “slips” and isn’t rusted together. ….or do you just turn the PTO off and rely on an internal PTO brake?

 

[workinonit]

I always thought the overun clutch was there to keep from burning the PTO brake up.