new member with a tractor problem

[birdsnest]

I just bought a 1984 ford 1710 with a 757a backhoe attachment. After only about an hour of use the dipstick would drift down after lifting it. After learning a little about hydraulic principles I have come to the conclusion that the problem is probably not the cylinder. The cylinder has no external leaks and I can't believe the cylinder could let the dipstick drop without hydraulic fluid going somewhere to allow the ram to displace the fluid. I feel like the relief valve or the control valve are the problem but don't want to disassemble anything until I have some avenue to get replacement parts. The six station control bank is made by Kontak, an English company that has been acquired by Parker. I called a Parker distributor in Salt Lake City and although he was helpful, he couldn't find any repair kits for this control valve. Is there a source for repair parts, seals, o-rings etc. for this old machine. I have the old parts manual and operators/trouble shooting manual for the backhoe attachment which gives me all the disassembly procedures and parts numbers. Thought this forum would be a good place to start. By the way, there are no external leaks anywhere on the machine

 

[TimberHole]

A hydraulic expert I am not. I’m sure someone with more smarts will be along shortly. That said, what makes you think the fluid isn’t going around the o rings on the piston? The first thing I would do is repack the cylinder.

 

[birdsnest]

the way I understand it, both the upper and lower hydraulics fittings on the cylinder go to the control valve for that cylinder and both should be closed in neutral position. This causes a closed cylinder which would not allow the ram to move either direction due to the fact that the oil cannot be compressed or drawn out. I am no expert either but want to be feeling good about my first move towards repair. when the ram moves inside the cylinder, oil must be drawn into or out of the cylinder or it can't move. The stick will drop from full extension in about 5 to 10 seconds. About 20 minutes before it started dropping so radically it took about 10 to 20 minutes to drop so whatever changed did so quite quickly. All other functions are normal Thanks for the reply.. And I may be wrong about the cylinder.

 

[TimberHole]

Even if both sides of the cylinder are closed the dipstick drops if fluid moves around the o rings from one side of the piston to the other. Again, not an expert but am I wrong here?

 

[birdsnest]

I think we are both going to learn something pretty soon. No way I would call you wrong with my limited knowledge.

 

[MHarryE]

How fast is the drop? Control valves are not zero leak and have a specified leak rate by the supplier. It only increases with time. Rebuild when it gets objectionable. An example for me is my mini-excavator. If I leave the bucked a foot off the ground at night, it will be on the ground in the morning. Same for all the hydraulic functions under load when stopped. Internal cylinder leakage across the piston is not normally a leak down problem. For example if the fluid from the piston end leaks across to the rod end, where is the oil going to go? Example - moving the piston end May displace 4 cubic inches of oil but for that same displacement, the rod end chamber makes room for only 2 cubic inches. A cylinder internal leak is normally seen as loss of function. Direct oil into the piston end and it blows past the seal and out the rod port which at that time will be open.

 

[mikester]

How fast is the drop? Control valves are not zero leak and have a specified leak rate by the supplier. It only increases with time. Rebuild when it gets objectionable. An example for me is my mini-excavator. If I leave the bucked a foot off the ground at night, it will be on the ground in the morning. Same for all the hydraulic functions under load when stopped. Internal cylinder leakage across the piston is not normally a leak down problem. For example if the fluid from the piston end leaks across to the rod end, where is the oil going to go? Example - moving the piston end May displace 4 cubic inches of oil but for that same displacement, the rod end chamber makes room for only 2 cubic inches. A cylinder internal leak is normally seen as loss of function. Direct oil into the piston end and it blows past the seal and out the rod port which at that time will be open.

Bingo!

Surprised by hydraulic leak down on a 1984 machine? I was surprised when I was told by GM that 7L of oil consumption every 5000km was considered “acceptable” for a gas engine...

You will probably spend more money chasing that leak down than the machine is worth.

 

[birdsnest]

Does anyone know of a parts source for the 757a hydraulic controller?

 

[Industrial Toys]

Unfortunately, pretty much EVERYTHING is loose and leaks on many old machines. I have used the worst of them. Good for a pail of oil a day, but still cheap to get a job done.

 

[birdsnest]

I don't care if it uses TWO pails of oil a day, I just want it to work. Lets see, what is cheaper, add another quart of oil or rebuild the engine. We all know the answer to that question. If I was looking for a brand new machine I would have forked over $30,000 but instead I paid $2,000 and now need the backhoe to dig. I can afford to put some money into this machine and am looking for a little direction.