Noise in 4020 differential lock

[Dreaming Green]

I have a 1966 4020, Diesel PowerShift.

When I engage the differential lock while moving, it makes a chirping noise. Sort of like a belt-driven pulley. The chirps have a cadence like a slow telegraph operator. Seems to come from under the operator platform. As soon as I touch the brakes, the noise stops.

Another clue: when I am standing on the ground with the engine running in Park, I hear an intermittent noise. Faint enough that I cannot hear it from the operator station.

Any ideas about what is happening here?

 

[Ray,IN]

Depends on how the lock is designed. Some use rectangular depressions and protrusions to create the lock. I can imagine if the edges are worn down it might allow the device to move a notch. For instance Massey Ferguson says to stop the tractor before engaging the lock, I'm not gonna do that when 2' feet deep in mud and tires already spinning. That's like tempting fate IMO.

 

[JIM MN]

The diff lock is oil pressure activated. Pressure low to engage diff lock, causing noise?? Check service manual how to hook up gauge, and what pressure should be and how to adjust if need? Troubleshoot? If pressure is good, problem must be mechanical? Something in valve or deep in differential, the lock pieces, or the differential itself- bearings= shafts or gears causing a noise when lock is engaged?

 

[used red MN]

Depends on how the lock is designed. Some use rectangular depressions and protrusions to create the lock. I can imagine if the edges are worn down it might allow the device to move a notch. For instance Massey Ferguson says to stop the tractor before engaging the lock, I'm not gonna do that when 2' feet deep in mud and tires already spinning. That's like tempting fate IMO.

Ray, the differential lock in a JD 4020 is a bit “less archaic” then the mechanical setups you are describing. The differential lock is an actual clutch pack that is hydraulically activated as Jim pointed out. See parts 12, 13 & 14 in the diagram linked below.
JD 4020 differential parts diagram

 

[Ray,IN]

Ray, the differential lock in a JD 4020 is a bit “less archaic” then the mechanical setups you are describing. The differential lock is an actual clutch pack that is hydraulically activated as Jim pointed out. See parts 12, 13 & 14 in the diagram linked below.
JD 4020 differential parts diagram

Got it.

 

[Fixingfarmer]

The diff lock is oil pressure activated. Pressure low to engage diff lock, causing noise?? Check service manual how to hook up gauge, and what pressure should be and how to adjust if need? Troubleshoot? If pressure is good, problem must be mechanical? Something in valve or deep in differential, the lock pieces, or the differential itself- bearings= shafts or gears causing a noise when lock is engaged?

Pressure should be supplied from a tee at the brake valve I had to swap rear ends on a 4020 once and and the front half of tractor did not have diff lock should be easy to follow from diff pedal and valve forward.

Should also be steering pressure I guess that would be another thing does steering act goofy if you turn all the way rapidly does it take a second to catch up to the wheel?

 

[Dreaming Green]

No issues with the steering when the noise is happening.
Hard to imagine what might be spinning fast enough in the differential to make a chirping noise.

 

[matthies]

Remove the plug behind the right side breakaway couplers and see if you can hear it better with the tractor jacked up and wheels moving. A second person would help and be safer. A pencil sized light would help also.

 

[Dreaming Green]

A tech from the dealer explained it: oil flow noise from a by-pass valve. He says that the pressure used to engage the diff lock piston is about 300 psi, so the normal pump pressure is reduced by a by-pass valve.

Fits the symptoms, but I would never have guessed that one.