WHY ???????????????

[pharmvet]

If I am correct:

Cat I setup uses 7/8" pins for the lift arm and 3/4" for the top link.

Cat II setup uses 1 1/8" pins for the lift arms and 1" for the top link.

Apparently, since this is standard, there must be a reason for it, but I would really like to know "WHY". It seems that it would be much more logical and less confusing for the lift arms and top link to be the same whether it be all 7/8" for CAT I or all 1 1/8" for CAT II.

Please explain to me why this is necessary. thanks

 

[Verticaltrx]

Larger tractors need the thicker pins on the Cat II to keep from bending them. Cat I came first (with the Ford/Ferguson in '39) then as tractors got larger they made Cat II, III and IV. As things progressed there was already a lot of tractors and equipment that was using Cat I, so they kept making the smaller equipment in those dimensions. It also helps to know roughly which equipment is compatible with which size tractor, although you can put one on the other.

 

[pharmvet]

I see the logic in larger pins for larger tractors / implements, but why not make the lift arms and toplink the same, regardless of size?

 

[chopped]

Basically make the top pin ""oversize"" to match the required lower you mean..Good question..

 

[pharmvet]

Exactly, what could be more logical and simplestic than 3 of the same sized pins (which ever size it may be) to hook up an implement?

 

[Brad_Blazer]

Some @#$%^& engineer figured the top link didn't need as much strength.

 

[gwdixon]

Many of the really heavy duty CAT 2 implements, especially the ground engaging ones, have a clevis-type lower arm hook up. The torque on the standard "stick out" pins in CAT 2 use can be tremendous. The mounts are usually of very heavy plate.

With a clevis-type hook-up, bending a pin could cause it to seize thus the beefier pin.

The top link rarely has the forces on it that the lower arms have. It is mainly used for lifting the implement or keeping the implement from rotating forward during use (unless you have draft control) and thus less stoutness. Not excusing the lack of a "single" pin that would fit all - just an explanation. Maybe it is an economic issue although the prices are not that much different.

You can change all of your implements to one size with a torch or plasma cutter if you like. I use CAT 3 to CAT 2 bushings welded in a cut hole to turn CAT 1 into CAT 2 for the clevis mounts.

The top link has an entirely different bushing but now that you point it out. It would be just as easy to weld in a large bushing and use one size pin.

If you saw some of the CAT 3 implements in use you'd know why their pins are so heavy duty. A CAT 1 pin wouldn't make it 5 feet without snapping or bending.

My CAT 2 implement hook ups are made from 3/4" to 7/8" bar stock to resist the twisting. The CAT 1 implements are 7/16" to 1/2" bar stock

 

[Verticaltrx]

I see the logic in larger pins for larger tractors / implements, but why not make the lift arms and toplink the same, regardless of size?

Yup, I misunderstood what you were asking. Some implements do use the same size pins all around, we have an older Gill box scraper that uses double captured pins for the lower links and they are the same pin as for the top link. IIRC our Deere #95 rear blade is also set up this way.

 

[crazyal]

I'm guessing it's cheaper to use 3/4" for the top link on a cat I. It's not just the pin but the rod end and the rod. Back when the standard was first set price of parts (over the labor cost to build) was a major concern. Once a standard was set it's hard to change.

 

[Baby Grand]

I'm guessing it's cheaper to use 3/4" for the top link on a cat I. It's not just the pin but the rod end and the rod. Back when the standard was first set price of parts (over the labor cost to build) was a major concern. Once a standard was set it's hard to change.

+1


Nobody who designs without keeping cost in mind stays in business for long. $5 here and there can add up to a lot over the bill of material of an entire tractor.

The smaller top link pin size means:

A cheaper top pin. Before standardization, and if you were a full line mfr, then this meant all your implements costs less to hook up.

Drilling a smaller hole in the top link position on the implement - less material/machining time/cost on all the imlpements you make.

Smaller top link - less material/less cost.

Since both ends of the top link are the same diameter hole - smaller hole on the tractor side top link mount - again, less material/machining time/cost.

All this cost reduction from one pin diameter change.

Welcome to my world - it ain't always pretty, but it keeps you on your toes.


PS - In my few dealings with real farmers I have always been impressed at how close to the bone they can operate just about anything. They make great engineers.