On springs and things:
The second biggest frustration with the HD-8 has been the springs.
The driver incorporates two long extension springs which, together with gravity, accelerate the ram downward to strike the post. You can imagine how I felt when the first spring broke while driving the 19th post, and the second spring broke while driving the 21st post.
I called Shaver because I imagined the springs should last much longer, but Shaver said the springs are not included in the warranty. They also reminded me that the springs need to be seasoned every day before use by cycling them 10-15 times. Yes, I did this every time. So, I bought replacements from the same dealer I bought the driver from, at $50 a piece, and I hoped the replacements would last longer.
They did - one lasted for the next 93 posts, and another for 100. Also, because the springs were breaking at the curved hook at the bottom, I bought some clips which are designed for a previous type of springs, and fastened them to the bottom of the broken springs to get some more use out of them before replacement. That worked for a while, but eventually they broke in other places and had to be replaced again. This time the dealer told me they no longer sold any Shaver equipment. So I found another supplier, but the springs were now $70 each plus $30 shipping.
By the way, most of the broken springs stayed in the channel when they broke, but two of them shot out the top. One of those landed draped across the hydraulic lines and did no damage, and the other flew up and over the tractor and landed between the hood and the bucket. It also did no damage, but one end of the spring plugged itself 2" in the dirt, so I was glad it didn't hit the hood. Or my head.
Replacing the springs is easy, as long as you don't follow the instructions in the manual. The manual tells you to disassemble and reassemble the post driver for spring replacement. This is baffling, since you can figure out how to replace them in the field and it only takes five minutes. You can also install a spring clip to repair the bottom of a broken spring pretty easily in the field. You definitely want a spare set of springs at all times. It is frustrating to lose days waiting on replacements.
So, why did the first springs break so early? For a long time I assumed they were from a bad lot, but I don't believe that anymore. Here's my theory. Most of the fatigue on the metal spring occurs at impact. That impact force is proportionate to the rate of deceleration, which is proportionate to the deformation distance (how much the post moves). So the impact force will double if deformation distance is halved.
So the long and short of it is, not only will poor soil conditions require more strikes on the post, but each strike will fatigue the springs more quickly. You can see how bad conditions quickly become a recipe for broken springs.
Another thing you can do to avoid over-fatiguing your springs is to quit when you are close enough. For example, if I am trying to drive the posts 42" into the ground, but progress slows dramatically near the end, as long as I have at least 36" in the ground, I quit and cut off the top of the post to fit. This saves time, frustration, and springs. I'm currently on my third pair of springs, and I'm up to 115 posts with this pair, with no breakage.