460 power steering

This is a two-part question, the parts of which may or may not be related. 460U has a vented plug above the power steering unit on the steering column. It leaks. I disassembled the PS unit and replaced the o-rings, it still leaks. The power steering valve itself is NLA. The plungers for the valve (if that is the problem) are $30+ apiece, it uses six. Since they fit in the bores in the NLA valve, I am not sure new plungers in worn bores would do any good. Any suggestions? I can replace the vented plug with a normal pipe plug, which will stop the leak, PROVIDED it does not force fluid up the steering column, and leak past the seal under the steeing wheel, or perhaps blow something else. Also, related or not, the filler cap for the whole thing, trans/diff/TA/power steering had the vent hole plugged. That cap will be replaced with a vented one. (The entire hyd system has had all worn parts replaced, everything except the leak in the PS works) The PS vent still leaks with the main system filler cap removed. Everything from the engine back uses Hy-tran, except the worm gears in the steering. The Operators manual says "torque amplifier fluid" (discontinued) or "worm gear oil". I am probably wrong, but I assumed worm gear oil meant SAE 90, which is in the gear unit (NOT the PS unit) now. I had the PS off yesterday, replaced the seals and reassembled. It appears to me that the SAE 90 and Hytran are mixing, as there is no seal on the shaft that enters the gear box. Is this my problem? There is only 1.25 pt of 90 to mix with 10 gal of Hytran. Tractor probably has not been run enough to cause damage, but if it is wrong, it needs to come out. Suggestions are appreciated. I followed instructions in the IT and Blue Ribbon Service manuals.

I've looked a little bit at the 460U steering as I also have problems with turning right (little to no assist) on my 460U. BUT I have turned no wrenches so take this with the appropriate amount of salt.

On general hydraulic principles, I'd say that the vented tank blockage could cause more problems than anything else.

I personally would not replace a vented plug with a sealed plug...this is bound to cause other serious problems. But: I think you are correct in your troubleshooting that a seal is leaking...somewhere the vented passage has a seal (or seals) and that's where the trouble lies IMHO.

"Worm gear oil" to me means "steam cylinder oil" which is classically used in industrial worm-drive gearboxes where there is bronze on steel. Mobil 600W is one such animal although Mobil SHC634 has replaced that mostly and can be bought in gallon jugs from McMaster Carr. If steel on steel (with no bronze anywhere) then "rear axle lube" ala 85W140 might be the best bet. However the EP additives in the "rear axle lube" will slowly "corrode" bronze if there is any present (and I can't say for sure).

Just in a quick "word" summary, my initial (simplified) impression of the 460U steering is as follows. Turning the wheel moves a spool valve, which is then re-centered by a set of springs. The spool is only offset from center as long as the wheel is being turned. When the spool is offset from center, this allows fluid to flow to either side of a piston depending on turning R or L. The piston is connected to a gear rack which supplies "assist" to the geared steering sector-arms.

I have seen the multiple outboard pistons in the diagrams and not 100% sure yet how this relates to the the explanation above. Once I get my shop built I'll probably tear it fully apart.

Thanks -- My concern about the worm gear oil is that it is contaminating the Hytran as there is no seal between the gear box and the power steering unit, at least not that I have found. I wonder if I shouldn't just use Hytran in the whole thing? The manual is rather vague on that. I am also hesitant to replace a vented plug, but since it is already leaking, there is nothing in the unit to damage except maybe to cause a bigger leak, which ultimately may come out the top of the steering column, but I don't think so. The unit has no springs, it does have a spool, the oil is directed left or right to the piston (which is connected to the rack) by the plungers and spool in the valve block. That is my oversimplified explanation, anyway. One thing I did not mention. This problem did not start until I hung a bush hog on the fast hitch after adjusting the Tel-a-depth so that it worked properly. It did not leak by just raising and lowering the empty fast hitch. That was before I realized that the previous owner had plugged the hole in the cap on the main reservoir -- but, the lift works fine. The PS pump on the 460 is mounted on the main hydraulic pump. The power steering works fine too, except for more pressure turned fully to the right. Not sure how all this ties together as to what pressure goes where.