Shear pin on post hole digger question

[perryjosh64]

Folks this is on an old post hole digger I was given. I m having to replace the PTO shaft. Finally got everything off and new shaft however the shear pin hole on gear box/old yoke is 5/16". On new PTO yoke hole is 3/8". Question is am I ok using 5/16 shear pin or do I need to drill out hole to 3/8" cause that would be a pain.

 

[K-Mo]

Also need provision to keep the PTO shaft on the gear box from disconnecting when pin shears. Some have snap rings on the gear box shaft.

 

[perryjosh64]

Yeah that came with new shaft. Just need to know if using a smaller bolt size (leaving space) through yoke will cause problems/unnecessary bolt shearing?

 

[Eric in IL]

Sloppy fitting shear pin holes are prone to shear the pin sooner than a good tight hole.

If possible, I'd rotate the yoke 90 degrees and drill a proper sized hole in the yoke.

If that is not possible, I'd weld or braze the yoke hole shut and re-drill it at 5/16.

 

[MARK ROBKE]

I would be afraid drilling the shaft hole bigger would weaken the shaft. I would also recommend brazing or
welding the yoke hole shut and redrilling. Mark.

 

[perryjosh64]

Yyeeaahh seems everything about this digger is a little off. Not only is the shear pin 5/16" (vs 3/8"), the drive shaft is 1 1/2" (vs 2" which seems to be standard). Got a piece of pipe cut/drilled to fill gap, so far it works.

 

[DoubleO7]

Got a piece of pipe cut/drilled to fill gap, so far it works.


LOL, yea I was thinking a 3/8 x 5/16 sleeve too.
Wet to McMaster Carr, looked up drill bushing, they have one with those dimensions. Very hard SS too.........$375 EACH

 

[Texasmark]

I wouldn't worry about it if you are a careful digger. Understanding what your soil conditions are, tractor HP, your digging RPMs and
your digging process has more to do with shearing the pin than the difference in hole diameters. BTDT

I like low RPMs, lots of cleaning out the auger as you go along (us and downs), final depth of dig, stop the auger, raise the 3 pt and
spin the auger, discharging the findings from the bottom of the hole in the surrounding area.

Why not jus use it as it is and if it breaks then worry about drilling out to 3/8.

Along these lines I have a Ford 3000 with Live PTO and Live is perfect for post hole digging especially digging in a line like would
be made for a new fence....just made for the job.