Rotary Cutter PTO yoke broke

[johndeerezach]

i was bush hogging just a littl bit ago and was mowing a hill and went to back down a little way to cut the top of the hill and hit a medium sized log and i raised it right when i hit it and i thought there was no harm done then i moved to a different spot to mow grass and when i started the pto the u joint broke and the part that connects to the spline on the tractor broke off the u joint. what did i do wrong anything helps

 

[leonz]

Hello John ,

I think the actual impact on the log was the
point where the yoke started to break and
the added stress of raising the mower
added to it and it snapped when you restarted it.

 

[RickB]

Service your slipclutch if your cutter has one.

 

[tessiers]

if the cutter went up enough to close the PTO shaft to the bottom will break the yoke every time.

 

[Dead Horse]

This may be an object lesson to setting up an implement properly.

The PTO shaft has to be cut to the proper length for the specific tractor, implement combination.

When you lift up on an implement the distance between the two spindles shortens. (tractor spindle and implement input spindle) IF the shaft is too long to allow that full retraction it will BOTTOM out and something will break.

Often times the spindle lock bends, deflects, breaks, resulting in it being VERY hard to get the shaft off the spindle on the tractor (as usually the implement end is through bolted and as a result tougher than the lock at the tractor end of the PTO shaft).

So, the lesson here is make sure when you install a new implement that nothing binds through the full range of motion on the lift, before you set out for work.

 

[johndeerezach]

the shaft was cut to the right length have taken it out already and am going to replace the yoke. but im pretty sure that the gear box should have a shear pin shouldnt it?

 

[tessiers]

every bush hog I ever saw has a shear pin usually 1/2" where the driveshaft bolts on the gearbox, or an eccentric flange thereabouts. A broken yoke is more typical of binding or bending than from over torque, unless defective or damaged prior to this incident.

 

[johndeerezach]

i dont think that it was binding because i lowered the mower and was backing up to cut near the hill and hit the log thats when the yoke broke when i engaged the pto after i hit it

 

[johndeerezach]

so the shear pin should be what attaches the pto to the gear shaft?

 

[Dead Horse]

so the shear pin should be what attaches the pto to the gear shaft?

Yes unless the mower came equipped with a slip clutch. All 6 of my mowers have some sort of slip clutch mechanism. In fact i do not recall seeing a bush hog (that was not at least 30 years old) without one.