706 power steering hydraulics lost prime

[jhncp]

I've had this problem several times after it sits, the hyd for power steering and brakes and TA don't work. The main hyd and 3pt do work. I had it running for an hour today, and tried compressed air in fill hole but I have no electricity there and only a air tank. I took the lower plug out and it's sucking. I think when it's pressurized it will burst out. I let it suck hyd oil in but still couldn't get it.

 

[Dieseltech]

Did you try the five gallon over the full mark trick?

 

[wore out]

.

 

[jhncp]

FWIW, the two pumps share the same inlet filter.

The hydraulic pump has primed first and is sucking hard enough against the filter that you notice suction at the OUTLET of the hitch pump!

Has the filter been changed lately? Any chance of ice restricting the filter or associated plumbing?

If it actually sucked oil into the OUTPUT of the hitch pump and it didn't prime it makes me wonder if the hitch pump isn't turning or is BADLY worn out.

The power steering works good when it's primed. If the main hydraulics are working good how good the filter be bad?

 

[caterpillar guy]

I've had that same problem.I have had it work and not work so well. IF you can get it out of the shed run it around in an open area in low 1st and turn the steering wheel as much as you can one way then the other and some times it will pick up and go. I find this happens more in winter than in summer so I'm coming to the conclusion I need to do a couple things one is change the hydraulic oil more often and change the filter more. I'm going to start that program this year and see how it works. There are a few reasons the filter could appear fine and remotes work and all. 1 is the distance from the filter to the steering pump for that to work. 2 there are more sealing surfaces to seal. Pump o rings in back of MCV and other o rings on MCV. 3 I believe the oil has to follow through the casting gallies to reach the MCV and steering pump. Meaning those gaskets and o rings could be getting hard from 50 years of use without being changed. 4 This would mean a rear split not at the clutch but at the range section to speed section. I never found the 5 gallon over did anything for me except require an extra 5 gallon of oil. Not saying it could not work for yours. IF that tube inside has a crack or leak it could since it would cover it in oil. I have not run my 806 in winter since I replaced all the springs and o rings in the MCV a couple years ago so could not say if it helped or not. What has always had me perplexed is it would work one time and not the next. in about the same temperature. Usually colder temperatures have more affect on it. I do believe it has to do with the amount of frozen moisture in the oil.Thus being the reason I think the more frequent oil and filter changing would help this problem. If the oil has a lot of moisture in it and the moisture freezes then flow would be effected so no steering. Mostly being the smaller passages in the MCV will slow down the flow. And the remotes flow directly to the valves from the pump not being restricted like the MCV would be. Best explaination and solution I can give. I'll wait and see if anybody agrees or has a better solution. There is a guy on U tube that has a remote plumbed so it goes into the bottom of the MCV and just puts pressure in there from the remote to prime it. I just see me loosing my remote use if I did that.

 

[jhncp]

I've had that same problem.I have had it work and not work so well. IF you can get it out of the shed run it around in an open area in low 1st and turn the steering wheel as much as you can one way then the other and some times it will pick up and go. I find this happens more in winter than in summer so I'm coming to the conclusion I need to do a couple things one is change the hydraulic oil more often and change the filter more. I'm going to start that program this year and see how it works. There are a few reasons the filter could appear fine and remotes work and all. 1 is the distance from the filter to the steering pump for that to work. 2 there are more sealing surfaces to seal. Pump o rings in back of MCV and other o rings on MCV. 3 I believe the oil has to follow through the casting gallies to reach the MCV and steering pump. Meaning those gaskets and o rings could be getting hard from 50 years of use without being changed. 4 This would mean a rear split not at the clutch but at the range section to speed section. I never found the 5 gallon over did anything for me except require an extra 5 gallon of oil. Not saying it could not work for yours. IF that tube inside has a crack or leak it could since it would cover it in oil. I have not run my 806 in winter since I replaced all the springs and o rings in the MCV a couple years ago so could not say if it helped or not. What has always had me perplexed is it would work one time and not the next. in about the same temperature. Usually colder temperatures have more affect on it. I do believe it has to do with the amount of frozen moisture in the oil.Thus being the reason I think the more frequent oil and filter changing would help this problem. If the oil has a lot of moisture in it and the moisture freezes then flow would be effected so no steering. Mostly being the smaller passages in the MCV will slow down the flow. And the remotes flow directly to the valves from the pump not being restricted like the MCV would be. Best explaination and solution I can give. I'll wait and see if anybody agrees or has a better solution. There is a guy on U tube that has a remote plumbed so it goes into the bottom of the MCV and just puts pressure in there from the remote to prime it. I just see me loosing my remote use if I did that.

I did get it out of the shed, and it builds up pressure in the steering if I turn it enough but I can barely get the tires to turn. The brakes don't work either unless I pump them alot they work a little bit. It seems this happens every time it sits for months. If I use it daily it's fine.

 

[DeltaRed]

Two things. First,change the hydralic filter. That filter serves both PS/MCV and hydralic/hitch circuits. When it gets restricted,the PS/MCV gets starved. Second,add 5 gallons over full of hydralic fluid. It may have a vacume/air leak in the ps supply tube. There is an Oring between the trans/rear end houseing that is above the trans oil level. 5 gal over puts the fluid above the oring. The oring can get hard and suck air but not leak oil.Common issue/problem and common 'fix'. Another possibility is your MCV/power steering pump is getting weak.They are not rebuildable. Replace with a new one.

 

[DeltaRed]

I did get it out of the shed, and it builds up pressure in the steering if I turn it enough but I can barely get the tires to turn. The brakes don't work either unless I pump them alot they work a little bit. It seems this happens every time it sits for months. If I use it daily it's fine.

The MCV controls the PS;brakes;TA and transmission lube. I'll bet the TA doesnt work either when it sits like that.

 

[DeltaRed]

The power steering works good when it's primed. If the main hydraulics are working good how good the filter be bad?

That one filter serves both powersteering and hitch hydralics. When the filter gets restricted the power steering circuit gets starved for oil.You cant see the 'dirt'/ restriction but it's there.I was taught (several years ago) that the first thing you do in similar cases is you change the hydralic filter.Many times that solves the issue. IH tractors are sensitive about that.

 

[DeltaRed]

The power steering works good when it's primed. If the main hydraulics are working good how good the filter be bad?

That one filter serves both powersteering and hitch hydralics. When the filter gets restricted the power steering circuit gets starved for oil.You cant see the 'dirt'/ restriction but it's there.I was taught (several years ago) that the first thing you do in similar cases is you change the hydralic filter.Many times that solves the issue. IH tractors are sensitive about that.