For info on the Hydraulink, check out the original thread. But be prepared to do some reading.
http://www.tractorbynet.com/forums/...-contained-air-over.html?highlight=hydraulink
I make it through page 15, almost went to sleep (mostly cause I was tired) it is a long read. Take away in a nutshell:
The Hydraulink (or HL) is basically a double acting hydraulic cylinder, plumbed so one port connects directly to the other port with a needle valve between. By closing the valve, the HL can be "almost" locked in any position within its 6" hydraulic stroke*. "Almost" as there is some air in the cylinder too, there has to be to get full stroke, as the cylinder capacity is naturally less on the piston rod or ram side of the piston than on the other side. The air provides some squish or "shock absorption", which many would think a detriment, it is claimed to be a feature and reputed to provide a smoother seat experience when towing a box blade etc. I can't remember feeling a need for shock absorption in my top link. This feature is also reputed to provide a degree of "self adjusting" - not sure how that would work though. . .
Because the aft most, rod, end has the least volume, and the welded ports are closest to the distal ends of the cylinder, and the cylinder in most installations is lowest at the tractor attachment, it may be assumed that the air will be, or mostly be, in the end nearest the tractor. Okay, lets say you are trundling along pulling a box scraper and the leading edge of the blade hits an obstruction of some sort (e.g. root, rock etc). The additional drag at the blade then tends to compress the top link. There is movement as the air compresses to a higher pressure, and the HL gets shorter. This movement then allows the blade to assume a *greater* angle of attack in relation to the soil, thus *increasing* the pressure and retraction of the top link. If this be the case, then the HL has positive feedback which would tend to make the operation *less* stable. Small obstructions or smoother soil would tend not to do this of course. I have no clue how the HL performs "real world", but I cannot imagine that the shock absorption, such as it is, would be beneficial. Please explain and correct me if I've got this wrong (it wouldn't be the first time :c).
To adjust the HL, you just reach around (maybe, if it's not too far) and open the valve. Gravity takes over and you close the valve when it's moved enough. Go to far? Start over by raising the implement.
To raise the implement, lower 3 point to ground (this may lose your "just right" 3 point position and require you start over with that - later. Once on the ground you can open the HL valve and drive forward. If all is well, the implement will tilt forward and you can close the HL. Raise the 3 point to where you liked it before, and proceed. Of course this assumes you can reach the HL.
*The HL has a 6" stroke and also a screw adjustment to get you in the ballpark. Not in the ballpark? . . . get out and screw. (My Cat-1 hydraulic top link has a 10" stroke - - no screwing around required :c)
The HL is an expensive step up from a mechanical screw type top link. Cost is about the same, or slightly more than a true hydraulic top cylinder with hoses, fittings and maybe a DPCCV. This assumes you have a rear hydraulic outlet already - if not, the cost of the rear remote may swing in favor of the HL.
The HL is being marketed as having it's own unique set of advantages, almost to the point where one might choose it over a traditional hydraulic top cylinder. IMO that's a bit of a stretch. I would rate the 3 options roughly on a scale of 1 to 10. Screw adjust = 1; Hydraulink = 3.5; Hydraulic top = 10
Some advantages of a true hydraulic top cylinder: Easy to adjust on the fly. Spreading the content of a box scraper is smooth and a beautiful thing, just extend top link for a fine adjustment of spread rate - more precise than raising the 3 point. Able to lift implements high for clearance when trailering etc. Easy to lift a brush cutter high enough to check blades etc (with adequate safety measures of course). The hydraulic top link makes brush cutting on uneven terrain much more doable.
Once you have a hydraulic top link, you won't want to go back. If you have a hydraulic remote, then a true hydraulic top link is the logical and best way to go. I you don't have a remote already, then consider getting an HL, though expensive for the convenience it offers over the old screw type.
bumper
