Where to measure PTO shaft diameter?

[Killscreen123]

Hey everyone!


I'm trying to buy an ORC for my 56 Ford 640 to use when I'm brush hogging my field. I want to be sure I buy the correct size to fit my PTO. I know the size is either 1 1/8" or 1 3/8", so I measured my PTO shaft yesterday. My problem is, where do I measure it from? When I measure the round part of the shaft with my calipers (not including the splines) I get 1 1/8", but when I measure spline to the opposite spline, it is 1 3/8". What size PTO shaft do I have?

Thanks!

 

[Sawyer Rob]

I've never seen a 1-1/8" shaft on a farm tractor, you have 1-3/8", 6 spline...

What's an ORC again???

SR

OK, I just figured it out, over run clutch... You guys and your abbreviations...

 

[Ford850]

I think those originally came with 1 1/8" shafts, but many were converted to 1 3/8" so an adaptor wasn't needed. That's why you'll see both 1 1/8" to 1 3/8" ORC, and 1 3/8" to 1 3/8" ORC listed.
So as long as you don't have an adaptor/extension on there and you measured that by accident, then you do need the 1 3/8-1 3/8" model.
Here are a couple examples of the adaptors:
SpeeCo PTO Increaser at Tractor Supply Co.
SpeeCo PTO Short Increaser at Tractor Supply Co.