Slip clutch vs shear pin
- Thread starter erda
- Start date
Russell King
Well-known member
Lifetime Member
Equipment
L185F, Modern Ag Competitor 4’ shredder, Rhino tiller, rear dirt scoop
Shear Pin -
Pros - simple, cheap, usually easy to replace, usually have to have one to connect the PTO shaft to the gearbox anyway
Cons - Can be replaced with incorrect strength bolt so is not really a shear pin any more, can be replaced with the incorrect length bolt and can fail at root of thread, can become lodged in the driven shaft's through hole and difficult to remove. When it fails, you have to take the time to replace it.
Slip Clutch-
Pros - Adjustable (can be set to slip at various slip levels), will slip as needed and then grip so there is no repair to take care of. If separate from PTO shaft, can be used on multiple implements.
Cons - more expensive, has to be maintained/adjusted or they do not perform their function. Have to adjust length of the PTO shaft to compensate for additional length (if not part of shaft).
Pros - simple, cheap, usually easy to replace, usually have to have one to connect the PTO shaft to the gearbox anyway
Cons - Can be replaced with incorrect strength bolt so is not really a shear pin any more, can be replaced with the incorrect length bolt and can fail at root of thread, can become lodged in the driven shaft's through hole and difficult to remove. When it fails, you have to take the time to replace it.
Slip Clutch-
Pros - Adjustable (can be set to slip at various slip levels), will slip as needed and then grip so there is no repair to take care of. If separate from PTO shaft, can be used on multiple implements.
Cons - more expensive, has to be maintained/adjusted or they do not perform their function. Have to adjust length of the PTO shaft to compensate for additional length (if not part of shaft).
The shear pin is almost idiot proof as long as you dont go using high strength grade 8 bolts.
The slip clutch pushes the u joints closer together and thus the angle they have to operate at is increased which shortens their life.
PTO angle of 5 deg has a life of 450 hours
PTO angle of 10 deg has a life of 195 hours
PTO angle of 15 deg has a life of 90 hours
PTO angle of 20 deg has a life of 40 hours
PTO angle of 25 deg has a life of 20 hours
A small change in pto shaft angle dramatically shortens the life of the u joints.
Dave M7040
The slip clutch pushes the u joints closer together and thus the angle they have to operate at is increased which shortens their life.
PTO angle of 5 deg has a life of 450 hours
PTO angle of 10 deg has a life of 195 hours
PTO angle of 15 deg has a life of 90 hours
PTO angle of 20 deg has a life of 40 hours
PTO angle of 25 deg has a life of 20 hours
A small change in pto shaft angle dramatically shortens the life of the u joints.
Dave M7040
I purchased a 48" rototiller as part of my BX-25D package. I already know how to work a shear pin, but the slip clutch, not so much. I either stall the tractor dead cold, not good, or smell burnt clutch when I'm done, likely not good either. I didn't expect a learning curve, and I have been running tractors for over forty years. This is my first tractor mounted tiller, and I do seem to grow more rocks than anything else... Your mileage may vary!
Jerry
Jerry
Thanks for the info.
Just to further confuse the issue, I've starting looking at tow behind, powered mowers-some of the area I need to maintain is the edge of a ditch and I've started to wonder if the slope might be a bit to steep.
Just to further confuse the issue, I've starting looking at tow behind, powered mowers-some of the area I need to maintain is the edge of a ditch and I've started to wonder if the slope might be a bit to steep.
Tallahassee Kubota Man
New member
Equipment
M5140HD/LA1153/LandPride RCF2072/DirtDog disc/RakeMaster grapple/Caroni tiller
Dave how much distance do you think the slip clutch would make? Never thought about it. On a bushhog that's 6-7' or larger the length of the pto shaft is quite long and wouldn't think it would change the angles that much. We've got an older 6' Bush Hog 286 with at least 800 hrs and never a problem with the u joints. Will have to take a look see to find the angles in that set up.
Mark
Most slip clutches will shorten the drive shaft by 6" or so. On an older bush hog, the slip clutch was likely standard equipment, most likely designed into the drive line. Shortening up the driveline on short shaft 3 point equipment isn't always the best idea...
I've got 8' and 10' brush mowers. Both have factory clutches right in front of the center gearbox. 6 ft. or so long PTO shafts, so it's all built into the design.
On second thought, maybe they were just slapped together without any design. They been around a while. Moses drug them through the desert with him on the way to the Promised land!! They've got a lot of miles on them.
On second thought, maybe they were just slapped together without any design. They been around a while. Moses drug them through the desert with him on the way to the Promised land!! They've got a lot of miles on them.
I was just about to post my question.
I have a B2650 with a 4' woods brush hog with a slip clutch. My mower is right at a year old with maybe 5-10 hours on it. Using it today in heavy stuff I stalled a couple times. I'm thinking I need to do a PM on the clutch and check to ensure it's slipping when needed. What say others?
I have a B2650 with a 4' woods brush hog with a slip clutch. My mower is right at a year old with maybe 5-10 hours on it. Using it today in heavy stuff I stalled a couple times. I'm thinking I need to do a PM on the clutch and check to ensure it's slipping when needed. What say others?
If you leave a slip clutch outdoors, or where it can get wet, it can effectively become a solid mass, glued together with rust...
Mark
I dont think in the situation you are considering the slip clutch will make a big difference. However, for likely $30 you can buy a simple plastic angle gauge like the one below:
With this tool you can just lay in on your pto shaft with and without the clutch installed and see how much change in degrees happens. This avoids the calculations necessary and is likely faster.
There are many experts on this forum, I learn all the time. My background as a mechanical engineer makes it easier for me to understand the theory but I would never want to fail to heed the advice of those with years of practical experience.
Dave M7040
Tallahassee Kubota Man
New member
Equipment
M5140HD/LA1153/LandPride RCF2072/DirtDog disc/RakeMaster grapple/Caroni tiller
If I'm understanding you right your concern is that your clutch doesn't slip when you load your tractor to the point of it stalling? The clutch shouldn't slip in that situation. It's made to slip when the blades come into contact with an immovable object, thereby protecting the drivetrain parts of the mower and tractor.
Tallahassee Kubota Man
New member
Equipment
M5140HD/LA1153/LandPride RCF2072/DirtDog disc/RakeMaster grapple/Caroni tiller
Dave, that's another tool I need........ err I want!Mark
I dont think in the situation you are considering the slip clutch will make a big difference. However, for likely $30 you can buy a simple plastic angle gauge like the one below:
With this tool you can just lay in on your pto shaft with and without the clutch installed and see how much change in degrees happens. This avoids the calculations necessary and is likely faster.
There are many experts on this forum, I learn all the time. My background as a mechanical engineer makes it easier for me to understand the theory but I would never want to fail to heed the advice of those with years of practical experience.
Dave M7040
Tallahassee Kubota Man
New member
Equipment
M5140HD/LA1153/LandPride RCF2072/DirtDog disc/RakeMaster grapple/Caroni tiller
Thanks. They've got a 1/2" drill on sale.....kill 2 birds with 1 stone.