s175 bucking when going into pile

[tubby's repair]

Need help on a s175 that is jerky when trying to push into a pile of dirt. Noticed that it will sometimes do it when taking off from a stop. Checked steering bushings and centering blocks. Charge pressure is 240 psi @ full throttle. Any help would be apriciated. Thank you, wes

 

[Tazza]

You checked the linkages at the pump too? the alloy blocks that bolt to the square shafts from the pump?
It does this when you move up slowly and keep pushing into the pile? No sudden movements or bashing the machine into the dirt at full speed? It should be smooth, the power shouldn't chance while loading it up slowly till the tyres start to spin.
As you mention it does it when taking off from being stationary, it really sounds like the alloy blocks. They bolts may be tight, but the shaft can wollow out the alloy linkage allowing it to move on its own. My S250 did this, i machined it and shimmed it.