mungus
Bronze Member
Hi,
My FIAT 780 has a lift problem! It had a fairly constant leak past the LHS lift arm bush, so I stripped and rebuilt the lift unit with new brass bushes and seals both sides. Added a new piston and O rings / Nylon seals etc for good measure whilst I had it apart. Great you'd think, should be better than ever. :thumbsup:
I wasn't worried about doing this job, as I'd previously had success replacing the shaft seals and removed and replaced the spool to cure a leak between it and the lift unit, all with no problems.
However this time when I reassembled the tractor and connected the hydraulic lines - no lift. Nada! There is definitely output from the hydraulic pump and there is oil getting to the spool valve and out the other side dumping back into the transmission case too. So it seems like it is bypassing the lift circuit, like it has an overpressure (?) circuit that is jammed open or something. My guess was that some silicon gasket had got into a gallery inside the spool valve that's mounted on the front of the lift unit. So using the factory service manual as a guide I stripped and cleaned it, blew it out with compressed air and replaced the O rings that I had matching ones for. Reassembled it all and ran the tractor - no improvement!
For a moment I thought maybe I had mucked up the control arms inside the lift unit, so I reassembled all that, again using the manuals (Parts manual very useful there, as the service manual really doesn't show how the linkages go together). Again, it all looked correct but alas no improvement.
In my efforts to find the cause I've now made the mistake of stripping the valve without measuring exactly how many threads were exposed on the sensitivity lever shaft too, so I'll have to set that up from scratch as well. All this is made so much more difficult with the 780 being a platform tractor, so you cant just run the engine and play with everything to get it working as you need to reinstall the platform and reconnect everything to get pressure to the lift unit... This is one area where the old "bare frame" type tractors are so much easier to work on.
The bummer is the factory repair manual has very little on the lift spool valve to help with assembly and set up. Few specs and only a couple of cutaway drawings of a generic spool valve that doesn't match mine exactly. My FIAT dealer confirmed that FIAT fitted several different spool valves to the 780/880 family and even some minor design changes of the lift units, (although they are all basically the same design).
None of the local dealers have a bench tester so it all got to be done on the tractor.
Not being a spool valve expert I was hoping someone here might have a nice PDF manual on them or some article on rebuilding such things, etc. Any help from a lift or FIAT specialist appreciated... :cool2:
My FIAT 780 has a lift problem! It had a fairly constant leak past the LHS lift arm bush, so I stripped and rebuilt the lift unit with new brass bushes and seals both sides. Added a new piston and O rings / Nylon seals etc for good measure whilst I had it apart. Great you'd think, should be better than ever. :thumbsup:
I wasn't worried about doing this job, as I'd previously had success replacing the shaft seals and removed and replaced the spool to cure a leak between it and the lift unit, all with no problems.
However this time when I reassembled the tractor and connected the hydraulic lines - no lift. Nada! There is definitely output from the hydraulic pump and there is oil getting to the spool valve and out the other side dumping back into the transmission case too. So it seems like it is bypassing the lift circuit, like it has an overpressure (?) circuit that is jammed open or something. My guess was that some silicon gasket had got into a gallery inside the spool valve that's mounted on the front of the lift unit. So using the factory service manual as a guide I stripped and cleaned it, blew it out with compressed air and replaced the O rings that I had matching ones for. Reassembled it all and ran the tractor - no improvement!
For a moment I thought maybe I had mucked up the control arms inside the lift unit, so I reassembled all that, again using the manuals (Parts manual very useful there, as the service manual really doesn't show how the linkages go together). Again, it all looked correct but alas no improvement.
In my efforts to find the cause I've now made the mistake of stripping the valve without measuring exactly how many threads were exposed on the sensitivity lever shaft too, so I'll have to set that up from scratch as well. All this is made so much more difficult with the 780 being a platform tractor, so you cant just run the engine and play with everything to get it working as you need to reinstall the platform and reconnect everything to get pressure to the lift unit... This is one area where the old "bare frame" type tractors are so much easier to work on.
The bummer is the factory repair manual has very little on the lift spool valve to help with assembly and set up. Few specs and only a couple of cutaway drawings of a generic spool valve that doesn't match mine exactly. My FIAT dealer confirmed that FIAT fitted several different spool valves to the 780/880 family and even some minor design changes of the lift units, (although they are all basically the same design).
None of the local dealers have a bench tester so it all got to be done on the tractor.
Not being a spool valve expert I was hoping someone here might have a nice PDF manual on them or some article on rebuilding such things, etc. Any help from a lift or FIAT specialist appreciated... :cool2:
