It looks like the pump was put together without a thrust bearing. The thrust washer is on the shaft. You need to replace the shaft. All the force pushing the machine forward goes through that bearing.
You can buy full rebuild kits with everything but the pump body. Make sure the kit is for the model you have.
The bearings need to be pressed in and out. Out is easy but they need to be pressed in to certain depths which makes things a little more difficult. They make a tool that seats the bearings to the proper depths, they are spendy and the job can be done with sockets, a hammer, patience and a depth guage of some sort.