</font><font color="blue" class="small">( Most likely it will not matter )</font>
Makes a huge difference.. do some research.
</font><font color="blue" class="small">( but on some tractors, the manual specifies to not use the bottom-most position )</font>
Toplink rockers are mechanical force amplifiers for feedback to the draft sensing mechanism. Your comment is so vauge as to be totally useless... That's like saying some cars use gas, when someone writes in and ask what fuel to put in their car.
What hole to use is based on where the toplink rocker pivots, and where the draft sensing mechanism is getting its feedback from, in relation to the pivot, and the toplink connection. For instance.. on an N, the bottom of the rocker is mounted and can rotate on a pin at the base of the rocker.. midway up the rocker, in the back of it, it is coupled to a draft plunger and spring.. this plunger is connected to the draft mechanism linkages under the hyd top cover. Now.. on the front side are 1 or more holes for the toplink.. the upper holes are higher up than the draft plunger, and thus offer the most mechanical advantage ont he plunger. These holes are for implements with very light draft, like a spring tooth harrow or small cultivator, that have such low draft, that you have to mechanically amplify it ( with a lever ) so that the draft sensing lift can be adjusted. Putting a heavy load like a 500-600 pound mower up in the top hole can actually damage the sensitive draft linkages under the lift cover by putting too much stress and range of motion on them.
Later ford designs like on their larger 5xxx and 7xxx tractors went to a toplink rocker that was connected and rotated on a pin at the top of the rocker, and then midway -down- the rocker was the draft plunger.. etc. In that example, the lowest hole would be the highest mechanical advantage, and the highest hole would be the least mechanical advantage.. etc.
</font><font color="blue" class="small">( I would suggest one of the middle positions )</font>
Late 8n fords only had 3 holes anyway.. however.. heavy loads are best placed on the lower hole for the 8n.
</font><font color="blue" class="small">( Also DO use the draft control and NOT the position )</font>
Draft control is almost exclusively for ground engaging implements. Anyone who has ever owned a ford 9n or 2n, or ferguson tX-20 can sure tell you that it is no fun to mow in draft control. Invariably they get a set of limit chains that attach at the toplink, and then run down to the implement pins.. you adjust the chain so that the mower is suspended at the level you want to cut at... that way you can mow without the mower dropping lower.. yet you can manually raise it with the 3pt lift to clear obstacles, then set it back down and know that you are mowing at the same height. A flexible toplink connection that adds a few inches of play is now included with most rotary cutters, so that the front of the mower can pivot a bit when the tractor is on uneven ground. Also, there were many add-on position control 'jigs' that will allow a draft only tractor using the ferguson system to function like it had position control. Most notably, one of the older ones was called 'the fergy positioner' A fellow retired ford tractor mechanic I know also makes and sells a device called a 'zane thang' Both of these devices bolt onto the lift housing and allow for extra external feedback so that the draft mechanism is automatically counter-adjusted so that it in effect.. it functions like plain old position control.
In draft control, say you went over a rise, then there would be more weight on the toplink.. the draft mechanism would interpret this as higher draft, and would lift the 3pt, and you would be mowing with a mower on the back that was bobbing up and down.
</font><font color="blue" class="small">( this way, if you hit a stump or other object, the bushhog will pick up automatically )</font>
Not neciscarilly. for the draft sensing mechanism on a ford ( or any ferguson system tractor ) to operate, there must be negative compression on the toplink for it to activate the lift. In the case of a 3pt mower, if the front of the mower strikes an object that won't move, the tail of the mower is going to try to flip up and rotate around the 2 lower lift points.. this will put the toplink in compression, and actually -lower- the lift.. not raise it. What you are thinking of is the analogy where a plow strikes a root or rock, and begins traveling under it, putting negative tension on the toplink, thus the lift would then try to extract the plow out of the ground.. hopefully before a tip breaks... or on later designs,.. the plow may trip .. etc.. 2 different scenerios, both with different directions of forces on the geometry.
</font><font color="blue" class="small">( and it follows the contours better. )</font>
Ford and ferguson system lifts on most tractors do not incorporate ground down pressure. Therefor if you set the lowest leverl you want your mower deck to be at, either with the position control, or by a limit chain, the mower deck is actually free to 'lift' on its own, as in -float- to follow the contour of the terain. If you doubt this, wal up behind a ford or fergy and ask the owner to rais the lift mid way, now grab the lift arms... you can freely move them up to max travel... they are not solidly coupled to the rockshaft that is driven by the hyd cylinder under the hyd cover, but are instead loosly coupled by a 'dogbone' that rides in the open ounth of the hyd piston, and is attached to the 3pt upper lift arm rockshaft.
I've got a 46 ford 2n, a 52 ford 8n, 54 dord NAA, 55 ford 660, 75 ford 5000 and a 2002 NH 7610s, and used to have a NH 97 1920.
The last substantial hyd repair I made on one of my tractors was 2 years ago on the 8n.. top to bottom.. 9 hour job to drain 5 gallons of oil, remove the seat, and lift link arms from the upper lift arms, pull the pto sahft, drop the belly pump, remove the top cover, remove the hyd cyl from under the top cover, disassemble the draft linkage and service the cam follower pin, add new gaskets to the hyd cyl, replace the oem 3 ring hyd piston with a newer oring/backup washer based piston designed for the NAA, dissasemble and clean the pump, reseal, replace relief valve, clean the sump, reattach the bellypump, reseal & reinstall the pto shaft and then reinstall the hyd top cover and align the control valve, and replace the side cover, reconnect lift link arms to upper lift arms, and drop the seat on. add 5 gallons of oil and go.
Not trying to be too 'hard' on this message.. except that I've helped people repair / repalce very expensive and sensitive draft control components on tractors for this very issue.. a rotary mower int he top hole... it can literally rip the 'guts' out of the hyd system. Most spectacularly is if the max travel linkage does not properly sense the piston movement at the end of the hyd cyl throw, the piston can be shoved out too far and damage lots of expensive little metal parts under the lift cover, not to mention making the relief open and or overtaxing the pump.. which by the way.. all those parts mentioned are NLS, except for the hyd cyl and piston.. the rest is pot luck via salvage and rebuilt parts.. Please try to be very specific, correct, and carefull when giving people advice that may well damage 800$-1000 in parts.. which is a average price for a salvage pump and top cover, piston, cylinder, and seals/gaskets and gooey stuff... not to mention the labor, and manual needed for repair and adjustment of the hyds after rebuild.
If you'd like to discuss more specific workings of the ferguson lift system let me know.
Soundguy
