Steve, I own a Worksaver HPD-20 SWO (offset hydraulic) that I run with my JD4700 CUT. I've driven approximately 1,500 posts with it in mostly sandy soil and it's performed pretty well. Many posts have been up to 8" diameter. My tractor's hydraulic flow is fine for the unit. The offset type has a balast box that you fill so the total weight is about 1800 lbs. This is as much as I'd want to lift with my 3PH. The HPD-16 SHC requires a tractor with a hydraulic system capable of 3-4 gpm at 1500 psi and no less than 35 hp. The unit weighs 723 lbs. You don't state if your NH-TDC-40 has a hydrostatic transmission but even if it does you should be OK (for hp). When the ram comes down the fluid has to be dumped immediately back into your tractor's hydraulic reservoir so the plumbing of the dump line is critical. I always have a loader on my tractor to counterbalance the weight and sometimes will the bucket to help depending upon terrain. For 400 posts, I would reconsider a PHD since this is considerably less expensive. The drivers, even with pointed posts, tend to have the posts wander if the ground is not uniform (rocks, roots, etc). Some of this can be corrected with the hydraulics. For normal fencing they are fine but for exact fencing (i.e. at the entrance of my farm) I used a PHD and string lines to accurately set my fences. I also used the PHD where the fences went through the woods due to many roots. Worksaver does stand behind their products. The master ram cylinder failed after a few hundred posts and they immediately sent a new one under warrenty. I was down for only a couple of days. The drive springs do break. One of mine broke around 1,000 posts so I replaced both. Kencove carries replacements. I've also bent two CAT 1 pins that attach the unit to my 3PH amazingly. I've set up to 120 posts in a day with a helper. Make certain your post tops are square and solid. Best of luck.
