Yanmar YM1510D – Front Wheel Assist Not Working

[SPYDERLK]

Thanks again for all the help so far—it’s been a huge benefit having this forum to turn to.

We spent more time on the tractor and ended up tearing into the front differential. The good news: we found no damage at all to the gears inside. That’s encouraging.

What seems to be the underlying issue is that the roll pin (shear pin) on the lower U-joint may have been the problem all along. I’ll be replacing that. You can see the sheared pin and before and after.
View attachment 3885664View attachment 3885665View attachment 3885666

I was surprised that the roll pin is carrying all that torque to those front wheels, but I suppose an engineer was thinking let’s make the fail point be a cheap piece to replace and easy to access (little did that engineer know I’d still rip apart the entire tractor!! )

Youre right.
A roll pin is a really bad choice for a torque limiter for several reasons; > it is an open section with spring temper (very hard), > it undergoes significant continuously varying torque in either direction actively working the section, > correct orientation of the pin relative to the torque force borne is critical and only alleviates the working. The pin will finally fatigue and break. Its inherent hardness is not good for the shear zone.

An appropriately sized and prepared shear bolt would be better.