Lift getting weaker

'48 8N front mount 6v positive ground.
Using a 3pt dirt scoop I used to be able to
back into a dirt/gravel pile and lift
whatever it could hold. Until recently,
that is. Sometimes if I try to scoop too
much the lift won't budge an inch. It's
also having trouble lifting roughly 700
pound round bails that it use to lift no
problem.

I changed the hydraulic oil since I had no
idea when it was last changed. I used the
modern 134 stuff. The hydraulic knock got a
lot louder (thinner oil, I know) and it
didn't change anything as as far as lift
capacity.

The lift still has full range of motion
with lighter loads. I put a round bail it
could lift on the spear and checked the
port. It does have some leak down from the
piston when the engine is off. I'd say a
heavy round bail would take about 10
minutes to fully drop down.

With the engine running, the leak was still
there with the lift half way up. For
whatever reason the leak would stop when
the lift was fully raised.

Fully raised, the lift would shutter/shake,
make a funny noise, and drop about an inch
all at the same time. Then it would quickly
recover back to full height and continue to
repeat the process. A slightly heavier bale
did the same thing but wouldn't even make
it to full height.

Whenever it faltered and dropped a bit, the
control arm at the pump would move on it's
own back into the pump then move back out
when it recovered. Touch control lever all
the way up, untouched.

Whenever it dropped, I didn't notice any
additional turbulence in the fluid, just a
constant slight swirl I assume is from the
PTO shaft. This tells me the safety relief
valve isn't the issue but I don't know for
sure. Or maybe the swirl IS the valve
leaking, dunno.

Any ideas? Thanks in advance.

Great diagnostics.

When the N lift is jerky coming up it means that one or more of the four pump cylinders is not pumping. It can be caused by broken springs in the pump chambers or a broken Scotch yoke in the pump that the pistons are attached to. Either one means the pump will need to be removed from the tractor to fix.
75 Tips

It doesn't jerk while lifting, only when it drops down because it can't hold the weight. It only drops an inch or two then recovers back to full height. Maybe jerking is a bad description for it.

Otherwise, it lifts smoothly. If I only had to lift lighter loads, such as my box blade, I wouldn't even know there was a problem other than the piston knock.

Hi Gambler.... Like Bruce said, good diagnostics on your part. I have to think your problem is the leaking you observe coming from the cylinder area. Do you have the I&T FO-4 manual? Good info in there on removing the top cover and overhauling your 70 year old cylinder. The swirling you see in the pump is normal from the PTO shaft like you said. If you saw churning or waves and bubbles that would be a concern.

Throw a safety relief valve at it, its gonna get one either way you go...

(quoted from post at 12:32:59 10/04/18) Hi Gambler.... Like Bruce said, good diagnostics on your part. I have to think your problem is the leaking you observe coming from the cylinder area. Do you have the I&T FO-4 manual? Good info in there on removing the top cover and overhauling your 70 year old cylinder. The swirling you see in the pump is normal from the PTO shaft like you said. If you saw churning or waves and bubbles that would be a concern.

Click to expand...

Thank you, sir. I'm thinking a new cylinder, NAA style piston/rings, and gasket set. They've all got to be toast after 70 years.