question 7745 hydraulic problems

[Darrell]

Just changed the hydraulic oil. The low pressure line of the three point hatch cylinder keeps jumping off. It seems as though the inlet is stopped up I’ve tried to blow air through the metal line in the picture. The fluid can not return so it blows the line off. Any ideal what would cause this I have a shop manual but doesn’t mention anything about the return line.

 

[diyfarmer]

Is that the return hose off the top of the assistor ram, that is coming off?

 

[Joachim]

Normally no oil should come out on this side (thin hose with hose clamp) because the lifting mechanism cannot press the external and internal lifting cylinders as single-acting.

On my Zetor 7340 (which is almost the same as the 7745) there is only a kind of ventilation valve on the cylinders instead of the line and that works too.

If oil comes out of the line, the inner sleeve seal of the lifting cylinder is defective and is letting oil through.
So remove the cylinder and reseal it. This is quite easy with these screwed cylinders and the sealing rings are standard parts.
You just need to measure the thickness of the chrome-plated piston rod once, then you will know which cylinder it is, because Zetor has installed 3 different ones here over the years.


For 32 mm chrome-plated piston rod:

74 - scraper ring 32 number 974583
75 - rubber ring 45x2 number974424
76 - guff 40x50 number 974479
76a - guff 40x32 number 974477
77- rubber ring 18x2 number 974504

 

[Darrell]

Is that the return hose off the top of the assistor ram, that is coming off?

I believe that is what it’s called

 

[Darrell]

Normally no oil should come out on this side (thin hose with hose clamp) because the lifting mechanism cannot press the external and internal lifting cylinders as single-acting.

On my Zetor 7340 (which is almost the same as the 7745) there is only a kind of ventilation valve on the cylinders instead of the line and that works too.

If oil comes out of the line, the inner sleeve seal of the lifting cylinder is defective and is letting oil through.
So remove the cylinder and reseal it. This is quite easy with these screwed cylinders and the sealing rings are standard parts.
You just need to measure the thickness of the chrome-plated piston rod once, then you will know which cylinder it is, because Zetor has installed 3 different ones here over the years.


For 32 mm chrome-plated piston rod:
View attachment 1898
74 - scraper ring 32 number 974583
75 - rubber ring 45x2 number974424
76 - guff 40x50 number 974479
76a - guff 40x32 number 974477
77- rubber ring 18x2 number 974504

Thank you on your parts diagram #104keeps coming off no oil is coming out of the tube but it is draining out the hose from the cylinder so if I understand correctly I need to rebuild the cylinder?

 

[Joachim]

Yes, so just remove the cylinder, disassemble it and put new seals inside: That should solve your problem.

 

[diyfarmer]

There is a small bit of oil comes out of that pipe, on my 8111 it seems to be when the arms have weight on them and you let the arms down to the last, but only a small amount. That pipe is only held with one hose clip on mine.

 

[Darrell]

Is that the return hose off the top of the assistor ram, that is coming off?

There is a small bit of oil comes out of that pipe, on my 8111 it seems to be when the arms have weight on them and you let the arms down to the last, but only a small amount. That pipe is only held with one hose clip on mine.

Yes, so just remove the cylinder, disassemble it and put new seals inside: That should solve your problem.

The metal tube it was connected to is that supposed to be open to the reservoir I tried to blow through a hose and was unable to. Just wondering if it was a vent that was stopped up.

 

[Joachim]

Normally the oil/air simply goes back into the differential through the upper hose, normally it should be open.

 

[diyfarmer]

The metal tube it was connected to is that supposed to be open to the reservoir I tried to blow through a hose and was unable to. Just wondering if it was a vent that was stopped up.

That pipe the assistor pipe is yoke to, on mine is about 3 inches long and has a banjo end on it. It is only a return going back to the backend.