755b hydrostat drive oil leak- any transmission guys out there?

[jkflatt]

Deere 755b leaking from left side transmission. Will attach pics. Does this sound like an O ring needing replacement and how difficult is it to replace?

 

[mg2361]

Yes it is an O-ring. The most difficult part is it has to be well marked and the turns counted so as to put it back on in the exact spot it was removed or you can cause a mistrack issue. Also the nut on the end of the servo can does not need to be touched. It is a stop for the servo and not a retaining mechanism.

Make sure to drain the hydrostatic reservoir or put a vacuum on it or you will get a bath.

 

[jkflatt]

Thank you so much for the detailed instructions! Will I need one or two o-rings? The diagram shows #18 and #17 o-rings. Also There appears to be a retainer clip where I circled in the pic. I assume it needs to be removed also. Can it be removed with removing the one screw as swing it out or will i need to find the top bolt on it also?

 

[mg2361]

Will I need one or two o-rings?

2

Can it be removed with removing the one screw as swing it out or will i need to find the top bolt on it also?

Both bolts and the retainer need to be removed.

 

[lantraxco]

Those bolts are tiny, and they take a star? socket. I recently did this exact repair on a similar Sunstrand pump and used an impact driver as a screwdriver handle, literally removed and installed them with one hand. Used a red paint marker, it's not as fussy as it sounds, make sure to grease the O-rings a bit and you will probably need to apply some pressure against the springs to start the threads. When you get your paint mark back up to the case, just line up the notch with where the little sheet metal lock was punched into it, no worries. Typically less than 500psi on the servo pistons, usually about half that.

The vacuum transducer is wonderful for this type of repair, I'm sure there are other tools, vacuum pump maybe, but CAT sells the air powered vacuum transducer to pull the oil back to the hydraulic tank. Just make sure the tank doesn't overfill from all the oil in the system, then it goes out the air exhaust of the transducer!
5P0306 or search for Air Vac on Ebay, lots of them at decent prices. Compressed air goes in the side port and out the exhaust on one end, the venturi creates a vacuum at the other end port.

 

[jkflatt]

Yes the retainer clip bolts took an E Torx socket. I got them removed and removed the hydraulic hose on top the servo can and stopped for the night. Will start again in morning. You kinda lost me on the vacuum transducer, is this a necessity? I’ve drained the tank of fluid.
Thanks for the help on this! So should I expect a spring or anything to pop out when I get the servo can screwed out?

 

[lantraxco]

No, if you drained the tank you will probably get minimal fluid loss.

No, the springs are caged on the piston, nothing should be loose in there.