The hydraulic pump on my 1966 John Deere 4020 (early model) is making a loud, screaming noise. I’ve lost steering, brakes, and the ability to lift. What steps should I follow to troubleshoot this issue? Preferably, I’d like to start with checks that can be done while the tractor is off since it sounds like further operation might cause damage.
There were no warning signs or prior issues leading up to the failure. On the day it happened, I was idling around the property with a light trailer attached to the hitch bar on the 3-point hitch arms, loading limbs and debris. I was starting, stopping, and occasionally raising the lift to dump the trailer. Sometimes, I left the tractor idling for a while, other times I shut it off and restarted it. The problem began suddenly and loudly on the last restart, right after cranking.
Any guidance on how to approach this would be greatly appreciated. Thank you!
Hey there! Sounds like a frustrating situation, but let’s take it step by step.
First, when was the last time you replaced the hydraulic filter or cleaned the sump screen? That’s always a good starting point. Drain the oil, then pull out the sump screen. You’ll find it in front of the left axle, toward the bottom. It’s about 2 inches wide, and you can loosen it with a 1/2″ breaker bar. If it’s really stuck, give it a sharp tap with a hammer—it works! Check if the screen is clogged.
If the sump screen looks fine, the next thing to check is the charge pump. To do this, remove the top link bracket on the back of the transmission case, then take out the plug behind it. You should see a hex shaft. Start the tractor briefly (just enough to check), and make sure that shaft is turning. If it’s not, the charge pump may not be functioning properly.
If both of those are fine, it could be an issue with the hydraulic pump drive coupler. Check for stripping there. Another possibility is a stuck relief valve, stroke valve, or diversion valve. These don’t usually fail all at once, but since your issue was sudden, it’s worth investigating.
Lastly, I’d recommend putting a pressure gauge on the system to check the hydraulic pressures before replacing expensive parts like the front pump. A lot of times, the root cause is a smaller, more affordable issue—like a stuck valve or a clogged screen.
If you don’t already have one, getting the John Deere SM-2039 service manual is a great idea. It’ll guide you through more detailed diagnostics.
Good luck, and let me know what you find!
Thanks for the help so far!
I recently bought this tractor and don’t have a solid maintenance history for it. The previous owner—a retired schoolteacher with a good reputation (although he might have enjoyed his homemade spirits a little too much)—told me he had completely serviced the tractor before selling it. This included replacing all fluids and filters. He mentioned it only had a few hours of use after the service, so he advised treating the service as if it had 10 hours on it when I got it. Since then, I’ve put less than 50 hours on the tractor. It looks to have been well-maintained, is in excellent condition, and has run perfectly until now.
Here’s my current plan:
- Inspect the hydraulic filter.
- Disconnect the coupling and turn the pump by hand to check for any obvious issues.
- With the coupling still disconnected, run the tractor and check for flow and pressure in the main pump supply line from the transmission pump by cracking the line coupling. (Is it necessary to measure the exact flow and pressure, or is it enough to confirm some flow exists?)
- Drain and inspect the hydraulic fluid.
- Check and clean the sump screen and the magnet inside it. (The previous owner said he added a magnet during servicing.)
- Refill with fresh fluid and install a new filter.
- Reconnect the coupling and recheck flow and pressure from the main pump.
- Cross my fingers that the issue is resolved without needing a new pump—since a rebuilt one from John Deere costs $2,200!
Do you think this approach works? Should I rearrange any of the steps?
I also have a couple of extra questions:
- Are NAPA filters acceptable, or should I stick to John Deere parts?
- Do I need John Deere Type 303 fluid, or are there suitable alternatives? Is standard tractor hydraulic fluid okay?
It’s much more convenient to get parts and supplies from NAPA or local oil suppliers than to drive to the nearest John Deere dealer.
Thanks again for the advice!
It sounds like you’re on the right track with your troubleshooting plan. Just a few things to keep in mind as you go through the steps.
The flow test from the charge pump can vary depending on the version of the tractor you have. For earlier models, the test is straightforward, but for later models, you might not need to remove the front pump coupling. If you’re not sure which version you have, check the splines at the front pump and coupling to see if there’s any wear or damage that could cause slippage.
Regarding fluid and parts: it’s a good idea to stick with John Deere-approved oils. Using oils that don’t meet JD specifications can cause serious problems, like damaging the brakes and introducing debris into the hydraulic system, which could lead to costly repairs. While some alternatives are available, it’s best to avoid anything that might compromise the tractor’s hydraulic and brake systems.
As for parts, the front pump is usually quite robust. Cracked cases are the main issue you’ll run into, which will show up as oil leakage. If you do need to replace the pump, it’s worth checking vendors like nnalert and Shoup for better prices than what you’d get directly from John Deere.
Lastly, if you’re hearing that “screaming” noise, it might not be the hydraulic pump itself, but rather the coupling spinning on the stalled splined pump shaft. This can happen if the coupling isn’t engaging properly, causing a loud noise.
Good luck with your repairs, and keep us posted on what you find!
Winner, winner, chicken dinner! 😀
The issue was indeed the coupling spinning on the shaft. It looks like the splines in the coupling were worn down, probably from the coupling slipping while it was spinning.
A question I have now: Why are the splines so shallow in the coupling? Is this the weak point, similar to a shear pin, or could it be that the bolts holding the split coupling to the shaft weren’t tight enough or loosened over time?
Also, how hard should it be to turn the hydraulic pump by hand? I can turn it, but not without some effort. It takes about an 8-10” lever arm to get it moving.
Thanks again for the help!
