If you’re a farmer who relies on combine harvesters to wrap up harvest season on time, you know how much rides on that big machine. A breakdown mid-harvest isn’t just an inconvenience—it can mean spoiled crops, missed market windows, and thousands of dollars in lost revenue. As someone who’s spent the last 12 years working with farmers as a combine harvester supplier, I’ve seen firsthand how small, easy-to-miss signs of trouble turn into costly, major repairs if ignored. The good news? Most of these red flags pop up weeks (sometimes months) before a full failure, if you know what to look for. Below, I’m breaking down the most common signs your combine needs repair, based on my experience fielding calls from harried farmers during harvest season and working with our team of certified service technicians to fix these issues before they derail operations. Combine Harvester
Let’s start with the part of the combine that does the heaviest lifting: the cutting and threshing components. I can’t tell you how many times a farmer has called me in a panic, saying their combine left half the grain in the field, only to find that the threshing rotor speed had been slipping for weeks without them noticing. First on the list: inconsistent grain loss. If you’re driving through a field and notice streaks of unharvested grain left in the rows, or your grain tank has more chaff and whole stalks mixed in with the good grain, that’s a clear sign something is off. This can come from a few different issues: worn rasp bars on the threshing cylinder, which are the metal bars that separate grain from stalks, or a misadjusted concave (the gap between the rasp bars and the cylinder that controls how much grain gets separated). I had a farmer in Iowa last year who brushed off streaky grain loss as “normal for heavy clay soil” until he lost 15 acres of wheat in a single day. When our technician inspected his combine, the rasp bars were half worn down, so they weren’t gripping the stalks to pull out the grain. Replacing those bars took three hours, and he was back to harvesting without another hiccup. The key here is that grain loss isn’t just about operator error—it’s a mechanical problem that worsens over time.
Next, pay attention to the engine performance. The engine is the heart of the combine, and any drop in power or unusual noise is a warning sign you shouldn’t ignore. I hear this all the time: “My combine runs fine at low speeds, but when I try to push it to harvest faster on flat land, it sputters and loses power.” That’s usually a clogged fuel filter or a dirty air filter, but it can also be something more serious, like worn piston rings or a malfunctioning fuel injector. Another red flag here is unusual exhaust smoke. If you see thick black smoke coming from the exhaust when the engine is running under load, that means it’s burning too much fuel—usually from a clogged air filter or a misfiring injector. White smoke, on the other hand, often points to coolant leaking into the combustion chamber, which can cause engine overheating and permanent damage if not fixed right away. Last harvest, a farmer in Ohio ignored white smoke for two weeks, thinking it was just “cold weather exhaust.” By the time he brought it in, his engine had seized up, and he was looking at a $12,000 rebuild instead of a $200 filter replacement. Small engine signs add up fast—engine issues don’t go away on their own, and they’re the most expensive repairs on a combine.
Then there’s hydraulic system problems, which are the unsung heroes of the combine. Hydraulics run the header lift, the feeder house, the rotor, and every moving part that lets you adjust the machine as you go through different fields. If your hydraulic system is acting up, the whole combine can’t function properly. The most common hydraulic sign I see is slow or unresponsive movement. If it takes 10 seconds for your header to lift when you hit the switch, or the feeder house moves sluggishly when you turn on the feeder, that’s a sign of low hydraulic fluid, a clogged filter, or worn hydraulic pumps. Another big red flag is fluid leaks. Hydraulic fluid is bright red or amber, and if you spot puddles under your combine after it’s been sitting, or wet spots on the hydraulic hoses or cylinders, don’t let that go. Even a small leak can drop your hydraulic pressure enough to cause a header to drop mid-harvest, or a rotor to stop turning while you’re in the field. Hydraulic leaks also pose a safety risk—hot fluid can burn you, and a sudden drop in pressure can make moving parts lurch. I had a farmer in Kansas last year who thought a small leak on his hydraulic hose was “no big deal.” A week later, the hose burst, and his header dropped into the unharvested corn, damaging the cutter bars so bad he had to replace the whole header at a cost of $8,000. A $50 hose would have fixed it before it got that bad.
Don’t forget the undercarriage and track or wheel systems, depending on what type of combine you have. For wheeled combines, worn tires or bent rims can cause all sorts of issues, like uneven ground pressure, which leads to compacted soil and inconsistent header height. For tracked combines, worn track pads or tensioners can cause tracks to slip, spin out, or even come off entirely in the middle of a wet field. I see this a lot during harvest in years with heavy rain—farmers push their tracked combines through mud, and the track tensioners wear out without them checking. If your combine is pulling to one side when you drive on flat, level ground, that’s a sign of uneven tire pressure (for wheeled models) or a misaligned track (for tracked models). Uneven ground pressure not only hurts your harvest yield, it also puts extra stress on the combine’s transmission and undercarriage parts, leading to premature wear. Last year, a wheat farmer in Montana called us because his combine was leaving uneven rows, and when our technician checked the wheels, two of the front tires were 20 PSI underinflated, which shifted the header angle. A quick inflation adjustment fixed the problem, and he avoided having to replace worn undercarriage components.
Another sign that’s easy to miss but super important: unusual vibrations or noises. Combines are loud machines, but you get used to the normal noise level after a while, so small changes stand out. If you feel a noticeable vibration in the steering wheel, seat, or floor when the combine is running at full power, that’s usually from an unbalanced rotor or worn bearings in the threshing cylinder. A loose bolt or broken tooth on a sprocket can also cause vibrations, which over time can damage other parts of the drive system. For noises, listen for grinding, squealing, or clunking when you turn on the header, engage the feeder, or shift the combine into high gear. Grinding noises usually mean metal parts are rubbing together because of worn bearings or lack of lubrication. Squealing is often from a slipping belt, like the fan belt or drive belt for the thresher. Clunking sounds, on the other hand, are a sign of loose parts—like loose cutter bars or worn universal joints in the drive shaft. I remember a farmer in Illinois who told me his combine was making a “funny clunk” when he turned. He thought it was just the rocks in the field, but when our service team inspected it, one of the universal joints in the drive shaft had broken, and if he’d kept driving, the entire drive shaft could have shattered, causing thousands of dollars in damage and leaving him stranded.
Finally, performance that’s way off from last year. If your combine is consistently harvesting less grain per hour than it did in the same fields last year, or you’re using way more fuel than you did during the 2022 harvest season, that’s a sign something is wrong. This can come from a number of the issues I mentioned above—worn threshing parts, a dirty engine, hydraulic problems slowing you down—but it’s a trend that shouldn’t be ignored. I always tell farmers to keep a harvest log: write down how many acres you harvest per hour, how much fuel you use per acre, and how much grain you get from each field every year. Comparing that log year over year can spot small drops in performance long before you notice a major problem. For example, if you harvested 12 acres per hour in 2022 and only 9 acres per hour this year, that’s a 25% drop that’s probably not just because of the crop—it’s a mechanical issue that needs fixing.
As a combine harvester supplier, my biggest piece of advice to farmers is this: don’t wait for your combine to break down mid-harvest to get it checked. Most of the repairs we do can be scheduled during off-seasons, like before planting or right after harvest, when you have time to get it fixed without missing critical harvest days. If you notice any of the signs I’ve outlined—streaky grain loss, sputtering engine, hydraulic leaks, uneven driving, unusual vibrations or noises, or drops in performance—reach out to our team to connect with a certified service technician. We offer on-site inspections, pre-harvest tune-ups, and emergency repair services to make sure your combine is ready to go when you need it. Don’t let a small issue turn into a costly, harvest-derailing problem—being proactive with your combine maintenance is the best way to protect your bottom line.
Agriculture Machinery Spare Parts References:
Combine Harvester Maintenance Guide. Agricultural Equipment Manufacturers Association, 2021.
"Common Combine Harvester Failures and Preventative Maintenance." Journal of Farm Machinery and Technology, vol. 45, no. 2, 2022, pp. 32-41.
Hydraulic System Best Practices for Agricultural Equipment. North American Farm Service Association, 2020.
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