Pros and cons of using an over run clutch/coupler on pto??

[JWR]

Not correct. engine braking with a diesel is much less than a gasoline motor of the same displacement, unless that engine is equipped with a compression (Jacobs) brake.

..and pto brakes usually are wet multi plate units, immersed in gearbox oil. Plenty of oil at all times.

With diesel compression ratios being much higher than gas why wouldn't the inherent braking be greater?

 

[JWR]

Hello all, I am hoping to get some feedback from people that use an over run clutch/coupler (ORC) on their tractors. I like the idea of saving the pto brake on shut down but was wondering if there is a down side to using them. Added stress or something else?

Also would like to know which ones would be best to buy if I decide to go that route?

Thanks in advance!!

Found this but not sure of the quality of this one or the manufacturer:

Amazon.ca

The only time I ever use and overrun clutch/coupler is on a 1954 tractor that lacks one internally. I tore up the PTO on that tractor once for lack of an overrun clutch. But I see no need for an ORC unless your tractor lacks one internally.

 

[CobyRupert]

Having a functional PTO should be expected and demanded when someone shells out big bucks for a machine.

For decades, tractors were designed so turning on and off the PTO didn’t snap shear bolts, stall tractors, burn up PTO brakes, or cause the need to repair the tractor or implement afterwards.

(…well, other than pushing an occasional tractor through a fence or into a pond. And an independent lever controlled PTO clutch solved that.)

IMHO, push buttons that slam on PTO’s and brakes that slam them off are a huge step backwards in tractor design.

 

[efox]

Hello all, I am hoping to get some feedback from people that use an over run clutch/coupler (ORC) on their tractors. I like the idea of saving the pto brake on shut down but was wondering if there is a down side to using them. Added stress or something else?

Also would like to know which ones would be best to buy if I decide to go that route?

Thanks in advance!!

Found this but not sure of the quality of this one or the manufacturer:

Amazon.ca

A lot would depend on what type PTO your tractor has. Live/braked/straight mechanical, and what type implement you are running. Older tractors w/o live pto tend to be pushed forward by the inertia of a wound up machine like a brush hog when the main clutch is disengaged and still in gear. An overrunning clutch allows it to wind down without doing that.
Now the unpopular opinion: there are conditions where using the good tractor brakes to stop that is preferable to letting the machine spin down. My life was saved this way once when I was wrapped up in a pto shaft on a tractor I was riding while being shown where the junk and ditches were. The boss was able to stop the brush hog rotation by leaving the tractor in gear and braking hard.
I know this is anecdotal but I don’t use one on my finish mower. It don’t spin as hard and my brakes are good. I can also kick the tractor out of gear anytime.

 

[Bentrim]

There a three types of PTO's.
1. Transmission driven. Tractor has a single disc clutch, Transmission and PTO start and stop together. Example N series Ford, older Farmnones, A, B, C, H, M etc, John Deere 2 cylinders before 1953 even some after, AC B, C, etc, Ferguson TO20 and TO30, almost all Massey Harris, most all tractors built before 1950, and a lot of early imports. These MUST have an over running clutch. Although a lot of aftermarket companies made a clutch that went on the differential and opened the drive to the rear wheels so the PTO could start before the transmission, this made the tractor more or less the same as a live PTO.

2 Live PTO Tractors with 2 stage clutch, 1/2 down stops transmission, complete down stops PTO, 1/2 way up starts PTO, complete up drives transmission. No need for an over running clutch as most have no brake.

3 Independant PTO Totally separate from the transmission. Controlled by a separate clutch, may be hand, or hydraulically engaged. If hydraulically engaged, you may engage by a lever-controlled valve or if electrically engaged you turn a knob or move a switch. Most of these have a brake to stop rotation when turned off. Some will NOT engage brake until the lever is moved far enough to apply it. Check your operator manual to check for operation, it should tell you if you if and when the brake is applied. If the brake is controllable, you don't need an over running clutch.

Most over running clutches that I am familiar with are mounted on the tractor PTO shaft therefore extend the shafts length and may be more likely to be bent or hit from something, it is possible it could cause a vibration or become out of balance. Most of the better quality and more expensive equipment that need them have over running clutches "built in". Rotary mowers though usually do no, and would need them the most.

 

[LouNY]

The older independent PTO's with a mechanical and or hydraulic linkage such as the IH 400's and up through to the 86 series you could ease the pto's on lock them up and use them then when disengaging it was up to the operator how much PTO brake was used.
These newer "improved" tractors with the electrically engaged hydraulic actuated PTO's are not as easy to work with most of them have no way to ease them on or off. Yes you can and should idle down before engaging or disengaging the PTO's but many of them still engage and disengage very harshly. If your implement does not have an over running clutch you may consider getting and using one, if you don't use it a lot and think that brake is durable and will be inexpensive to replace don't bother, or just for the heck of it ask your dealer how much to replace the PTO brake, you may reconsider.

 

[5030]

With diesel compression ratios being much higher than gas why wouldn't the inherent braking be greater?

Because a diesel creates no vacuum in the cylinders hence no braking power. What a Jacobs brake does, it holds a valve slightly open so the cylinder(s) can draw in air and create the vacuum. Also why they won't work as the engine is accelerated.

 

[5030]

Most over running clutches that I am familiar with are mounted on the tractor PTO shaft therefore extend the shafts length and may be more likely to be bent or hit from something,

I'd like to see that. How do you do that, back into a brick wall??? I run an ORC on every implement that don't have one built in and I also have a friction clutch on my shredders.

 

[JWR]

Because a diesel creates no vacuum in the cylinders hence no braking power. What a Jacobs brake does, it holds a valve slightly open so the cylinder(s) can draw in air and create the vacuum. Also why they won't work as the engine is accelerated.

I do not follow that: Certainly the diesel creates a vacuum, otherwise the air would never be drawn in through the intake valves. The vacuum is produced on the intake stroke as it would be normally and as it is in all internal combustion engines be they diesel or otherwise. Then the Jake brake system (in braking mode) holds the EXHAUST valve partly (abnormally) open as the piston approaches TDC on the compression stroke. [NOT to let air be drawn in but rather to adjustably control the already compressed air as it leaves via exhaust. ] Instead of firing fuel via the heat of compression the air in the cylinder is exhausted through the exhaust valves. In effect using "back pressure" to accomplish engine braking.

Of course Jake brakes do not work as the engine is accelerated because during acceleration the compression stroke compresses the air to the point of being hot enough to ignite fuel and the injectors then inject fuel at the timed moment which explodes, causing the power stroke as the piston goes back down. That would not happen during Jake braking because the exhaust valves are "prematurely opened" intentionally to release air nearing TDC on the compression stroke. The timing is of course adjustable so that the operator can control the slowing effect of the Jake brake.

 

[LouNY]

A diesel has no butterfly on the air inlet, hence no restriction to create a vacuum.