TN75 Transmission & PTO Issues

[mustangmarty1967]

New to me New Holland TN75 needs work.

Are the front and rear hydraulic pumps the same part number? The loader and 3-point hit hitch work, but the transmission won’t do anything and the PTO makes a loud clicking sound.

Buddy of mine put hydraulic oil that was contaminated with water. Already flushed it all out and replaced both the main hydraulic filter a few times and the transmission/shuttle filter as well.

 

[muddyblue]

Water contamination can really wreak havoc on hydraulics. It likely damages seals and rusts internal parts. On the TN75, front and rear pumps usually have different part numbers. That clicking noise from the PTO and the dead transmission probably indicate clutch pack damage from contaminated fluid eating away at the friction material.

Unfortunately, you might be looking at some serious rebuild work.

 

[Braingrain]

Flushing can help, but if water's been sitting there for a while, the damage might already be done. Check the service manual for the pump part numbers, as they typically have different specs. You’re probably going to need to tear down the transmission to fully replace the damaged clutches and seals.

 

[bluehayday]

Water in hydraulic oil can be disastrous. It leads to rust, breaks down seals, and emulsifies the fluid. Even after flushing, corroded parts can keep failing. That clicking from the PTO is likely due to a damaged clutch. Before you start replacing parts, it’s smart to get a diagnostic from a dealer. The damage from contamination can spread internally, so it might involve more than just swapping out the pumps.

 

[mustangmarty1967]

The contaminated fluid was running in the tractor for only a few minutes before my friend told me the fluid he poured in didn’t look too good. I immediately shut down the tractor and drained the fluid from both drain plugs, (milky fluid came out), replaced the main filter, (didn’t know about the second transmission filter at the time), put in fresh fluid, ran it until it warmed up, drained again (clean fluid came out this time), replaced main filter again, refilled with more new fluid, ran till warmed up again, drained (clear fluid again), new main filter again.

After all that (over $500 worth of fluid and filters) the transmission was working, but only after the tractor reached normal operating temperature. Upon start-up I can hear a whining sound coming from the power shuttle control valve body for a few seconds where the pipes come in that run from a filter housing on the right side of the frame. That’s when I learned about the filter for the power shuttle control. I replace that with a new one, but it didn’t make any difference. I can still hear whining coming from the power shuttle control valve body on the left side of the transmission under the seat behind the left rear wheel. It only last for a few seconds, then quiet down.

I did loosen the banjo bolt on top of the rear hydraulic pump the feeds the transmission, and started the tractor to see if it was moving fluid. It IMMEDIATELY sprayed fluid EVERYWHERE. So it’s definitely moving fluid. No idea at what pressure or flow rate though. It’s supposed to be around 4.5-5.3 gpm. So it is definitely a different part number from the front pump. I even have the part number now too.

Do y’all think there’s a chance that the power shuttle valve body-solenoids might be sticking and that removing it and cleaning it out might get my tranny working again?

Or could it be something electrical. I did pressure wash the whole tractor where it sits. Maybe I knocked a sensor wire or electrical connection loose somewhere? I know the seat sensor is working because it always beeps 14 times loudly when I get up from the seat. Also the brake light was on, so I check the brake fluid reservoir and it was sitting at an angle. I straightened it, and the brake light went out. Also, the power shuttle light was flickering, but went out after I replaced the filter for it that was in the filter housing on the right side of the frame.

 

[Alan]

Did some digging and this is what I found, hope this helps.

Given everything you've done, the cold-start whining points to residual air or a sticky power shuttle valve.

Here's where I'd focus:

The whine clearing after warm-up strongly suggests the solenoids or valve body are gummed up, contaminated fluid leaves varnish residue even after flushing. Pulling and cleaning the shuttle valve body is absolutely worth trying before replacing anything expensive.

On the electrical side, that pressure washing is a real suspect. Check every connector around the shuttle valve and under the seat, corrosion or a loose pin there can cause erratic solenoid behavior that mimics mechanical failure.

Quick priority list:

Clean the shuttle valve body first, then systematically check each electrical connector in that area with dielectric grease on reassembly. If the whine persists after that, you're likely looking at pump pressure/flow testing to rule out the rear hydraulic pump being compromised.

You're actually pretty close, the fact that it works once warmed up means it's functional, just struggling cold. That's a gummed valve, not a dead one.

 

[mustangmarty1967]

Sounds like a plan. I’ve been looking but haven’t found any procedures for removing the power shuttle valve body. Is it as simple as just draining the hydraulic fluid, disconnecting the lines, and unbolting it from the side of the transmission? Are there any springs or tiny check balls I should be prepared to catch when they go flying? Here are a couple pictures of where the whining sound is coming from, which I’m assuming is the power shuttle control valve body…

 

[mustangmarty1967]

I replaced all of the fuses. After that I got a trouble code 81, so I replaced the transmission oil pressure switch, and the transmission started working again. The brakes work well as well. However, the PTO still makes the loud clicking sound. I’m considering running it the way it is. Would doing this cause more costly damage to the PTO?