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786 hydraulics


New Englander

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Hi,

I'm new to the forum although I've searched it in the past. I have a couple of IH industrial machines and have recently acquired a 786 tractor.

The new-to-me 786 has some hydraulic issues. It has very little pressure to the remotes, it looses steering at low rpm after being worked and the hydraulic fluid seems to have lots of air in it.

I've changed the filter - it was quite dirty and have ordered manuals for it. Are there any areas that commonly cause these symptoms?

Thanks!

Jim

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Hi,

I'm new to the forum although I've searched it in the past. I have a couple of IH industrial machines and have recently acquired a 786 tractor.

The new-to-me 786 has some hydraulic issues. It has very little pressure to the remotes, it looses steering at low rpm after being worked and the hydraulic fluid seems to have lots of air in it.

I've changed the filter - it was quite dirty and have ordered manuals for it. Are there any areas that commonly cause these symptoms?

Thanks!

Jim

Could be the Oring at the pump mount or oil pick up tube, also the Oring between the speed & range trany could be bad.

Do the brakes work?

Ray

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Hi,

I'm new to the forum although I've searched it in the past. I have a couple of IH industrial machines and have recently acquired a 786 tractor.

The new-to-me 786 has some hydraulic issues. It has very little pressure to the remotes, it looses steering at low rpm after being worked and the hydraulic fluid seems to have lots of air in it.

I've changed the filter - it was quite dirty and have ordered manuals for it. Are there any areas that commonly cause these symptoms?

Thanks!

Jim

Could be the Oring at the pump mount or oil pick up tube, also the Oring between the speed & range trany could be bad.

Do the brakes work?

Ray

Hi Ray,

A couple of times when turning, clutching, and braking at the same time, I momentarily lost all then got them back.

The fluid that drained with the filter change was very milky. Some postings on other forums suggest overfilling by 5 to 10 gallons will "correct" the problem but that's not the way I do things.

Since the filter looked so clogged I wouldn't be surprised if an O ring got destroyed in the suction side. How much time/trouble to pull the pump? The machine is low time and runs excellent - easiest starting diesel I've ever seen. It's also been neglected. I've already tended to a half dozen easy fixes.

Are there any service bulletins that address this and where can I search them?

Thanks!

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Hi,

I'm new to the forum although I've searched it in the past. I have a couple of IH industrial machines and have recently acquired a 786 tractor.

The new-to-me 786 has some hydraulic issues. It has very little pressure to the remotes, it looses steering at low rpm after being worked and the hydraulic fluid seems to have lots of air in it.

I've changed the filter - it was quite dirty and have ordered manuals for it. Are there any areas that commonly cause these symptoms?

Thanks!

Jim

Could be the Oring at the pump mount or oil pick up tube, also the Oring between the speed & range trany could be bad.

Do the brakes work?

Ray

Hi Ray,

A couple of times when turning, clutching, and braking at the same time, I momentarily lost all then got them back.

The fluid that drained with the filter change was very milky. Some postings on other forums suggest overfilling by 5 to 10 gallons will "correct" the problem but that's not the way I do things.

Since the filter looked so clogged I wouldn't be surprised if an O ring got destroyed in the suction side. How much time/trouble to pull the pump? The machine is low time and runs excellent - easiest starting diesel I've ever seen. It's also been neglected. I've already tended to a half dozen easy fixes.

Are there any service bulletins that address this and where can I search them?

Thanks!

If the hytran is milky, change it.

It has some water in it and maybe been over heated.

Milky hytran don,t work well.

Ray

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Your tractor has two independent hydraulic systems that share a common filter and reservoir. If you are getting air into the system the pumps will be unusually noisy.

Problems with the remote pressure will be caused by a bad relief valve, leaking O-rings, or a bad pump. The best way to check the relief valve is to swap it with a known good valve. The pump is located opposite the hydraulic filter. The O-ring that causes the most problems is located between the rear frame and the cover on which the pump is mounted. A blown O-ring between the pump and cover is also possible. If the relief valve is good and the O-rings are not blown out, change the pump.

The problems with the steering and brakes is typical of what happens with a worn out MCV pump. A blown O-ring between the MCV and center section can also have the same symptoms but they are usually more pronounced and will appear even with cold oil. A worn MCV pump also results in loss of lubrication to the range transmission and ring gear and pinion.

The reason for adding additional oil is to compensate for a leaking O-ring between the rear frame and center section. The symptom of that O-ring leaking is loss of prime on the MCV pump when the tractor is first started after setting idle for a while. Sometimes a week or two of non-use is necessary before this appears.

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I at first thought that the milky look was strictly due to air - there were visible bubbles in it. Now, after sitting overnight it is uglier. No water has yet to settle out of it so I don't think that's the problem. It must be some terrible mix of various oils and???

My plan is to remove the hitch pump and inspect the suction side, clean out the case and change the fluid and filter. I don't think I have a cartridge relief valve that's the same as this one but I'll pull it and inspect it anyway. I have had one stay open with a piece of what i think was a piece of old O ring stuck in it. That was in a loader.

If I don't find anything obvious in the hitch pump and new fluid is no help, I'll start on the MCV. It is showing a brake wear light so maybe there's some extra demand there when they're applied. Those will get changed as well.

Thanks for the help and, if anyone thinks of anything else, I'd love to read it! I've been perusing the posts here and it's plain to see there's some experience talking.

Jim

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If the hydraulic oil is milky it's a pretty sure thing that it is contaminated with water. If they get that bad the oil won't necessarily separate back out of the oil. Change it, and if it were me I'd put another clean filter in. When you refill don't be afraid to go 5 gal past full. The extra oil will help greatly in lubricating the rear end.

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The more that I think of it and the more folks who tell me, I agree that it must be water and ?? It's just that I expected to see at least some separate out the bottom. This stuff is pretty well homogenized. It certainly holds water in suspension, not like engine oil or ATF.

How would water get into the system? I've had water-oil heat exchangers go bad and fill transmissions up with water (it get pretty pink but settles out), but this machine seems to have an air to oil cooler. Maybe someone got carried away with a pressure washer.

Anyway, It will have to wait a week or so until parts arrive and I get time to get back to it. I'll certainly post my findings.

Thanks all for the help!

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For starters you live in a part of the country where you actually have a winter. Under the right conditions in the fall and spring you will see sweat all over the outside of the tractor. That tractor is seating just as much on the inside as it is on the outside and the moisture has no where to go. So if the hydraulic oil hadn't changed for a number of years, or never that would explain why it was so contaminated.

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For starters you live in a part of the country where you actually have a winter. Under the right conditions in the fall and spring you will see sweat all over the outside of the tractor. That tractor is seating just as much on the inside as it is on the outside and the moisture has no where to go. So if the hydraulic oil hadn't changed for a number of years, or never that would explain why it was so contaminated.

None of my other IHC industrial or green AG machines have water in them so I don't think condensation is the culprit. They do sweat or frost a lot. Condensation would require substantantial amount of air movement. The vent will allow some movement as atmospheric pressure changes but that really only amounts to the column of air in the tube. A certain amount will be drawn in as the tractor cools as well. This is a substantial amount. Maybe it was accidentially induced or the machine may have been partially submerged.

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New Englander - I'm going to agree with Old Three Bottom, I think the moisture is from condensation, or the tractor sat outside a lot. From what you've said it's really likely the oil is the factory fill oil from thirty years ago when the tractor was built at FARMALL in '80 or '81. The "equivilent" oil for your green ag tractors is formulated to NOT mix with or absorb water. But since water or condensation is a fact of life for outdoor power equipment IH spec'd Hy-Tran to absorb some water.

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Well Doc, I'll take your word for it. Whatever the cause, the stuff will be changed and hopefully, the problem solved.

My 3616 has Hy-Tran in it, (assumedly), sat neglected outside for years before I took pity on it, but it had relatively clean oil in it when I changed it, that is, no water suspended or free in the sump. The previous owner had not even changed the engine oil for years.

Anyway, I'll report when I finally get the time to change it, check the pump, etc. It's parked for the time being.

I do appreciate the help/suggestions.

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