FIAT lift unit oil leak

[mungus]

Have a problem with my FIAT 780 leaking oil past the LHS lift arm seal.

It had this problem when I bought it years ago. So when I restored it I replaced both lift arm seals, along with the lift unit piston seals / rings, and that reduced it somewhat but its got bad again.

Usually it just drips leaving a wet LHS diff housing etc but recently I've found that if you lift a big weight (say a linkage sprayer) with it the drips become a thin stream! Losing quit a bit of oil this way and the lift setting has become more sensitive too.

My theory is that the lift piston and / or sleeve is worn and that this is allowing a lot of oil to blow by and pressurise the lift housing.
This oil under pressure then finds its way out through the weakest seal...
Possibly this is assisted by reduced (partial blockage) case venting, that would normalise sent this overpressure back through to the bevel shaft housing.

Any theories? Or better still anyone experienced this problem on a FIAT 80 series and managed to fix it?

Thanks in advance. :dance1:

View attachment Fiat780HydLift.pdf

 

[mungus]

Well found the culprit. The large bush on that the cross shaft rides in. The OEM one was aluminium, the replacements are brass.
When I got the lift unit out on the bench there was quite noticeable play in that bush. The RHS one was OK.
They are not cheap from FIAT but should last a very long time. I renewed the lift piston, cross shaft seals and all "O" rings etc, at the same time.

 

[2458n]

I have a 640 Fiat that was sold as a white field boss 60-2. This is a great tractor with a power steering leak.So could you tell me where to get seals for this?

 

[mungus]

Not a 640 guy so no I cannot tell you from memory, but there are plenty of places selling FIAT parts and the 640 was common in its day. A google search will likely find one handy for you to use.

Every FIAT seal I have seen so far has been a standard metric size, available through my local seal and bearing supplier. Often cheaper that way too. If you are in the US you could try import tractor parts, they specialise in FIATs.

Your Fiat-built Tractor Parts Source!

If it was me I'd just remove the offending seal and take it to a seal supplier to match up. The dimensions are usually shown as 3 spaced sets of figures on the seal face. It's likely just a standard rod seal...

See the photo attached, those figures mean;

OD - 30 mm & ID - 22 mm & Thickness of - 11 mm



Hope that helps.

 

[2458n]

Thank you for your quick reply.It was bought second hand and has served well for my uses. Our local rebuilder has one employee who does the work and a owner who does the pricing. I will proceed as you have directed.