Most Common Cause: Planetary Gear Assembly Wear
In 44 years, I've diagnosed grinding mixer noises hundreds of times. The planetary gear assembly is the culprit in roughly 65% of cases. These gears drive the agitator shaft in a planetary motion around the bowl, and they take tremendous load every shift.
The planetary assembly consists of a ring gear, pinion gears, and a planetary shaft. When the grease breaks down or gets contaminated with flour dust or sugar, the gears start running dry. You'll hear a grinding or growling sound that gets worse under load. On Hobart A200 and A200T models, this typically shows up around 8-12 years of heavy use.
You can confirm planetary wear by running the mixer empty at speed 1, then again at speed 3. If the grinding gets noticeably louder at higher speeds, that's planetary gears. The noise will be loudest at the top of the mixer near the bowl-lift mechanism.
What You'll See When You Open It Up
Pull the motor cover and planetary housing. You're looking for metal shavings in the old grease, pitting on the gear teeth, or in bad cases, completely stripped teeth. I've seen planetaries so worn the pinion gears were riding on the shaft instead of the gear teeth. If there's any metal contamination in the grease, the whole assembly needs replacement. You cannot just repack it.
Parts cost for a complete planetary assembly runs $380-$620 depending on mixer size. Labor is 2.5-3.5 hours if you're experienced. For Hobart mixer repair, we stock planetary assemblies for A200, HL200, and Legacy+ models on every truck.
Bearing Failures: Front and Rear
The second most common source, maybe 25% of grinding noise cases, is bearing failure. Commercial mixers have bearings at the motor shaft and at the worm gear housing. When these fail, you get a grinding or squealing noise that's constant, not load-dependent like gear wear.
The front bearing supports the agitator shaft where it exits the planetary housing. This bearing sees side load from the bowl tool, especially with heavy dough or if operators are scraping the bowl while running. Hobart part number 00-437936 is the standard front bearing for A200 series. When it fails, you'll feel radial play in the agitator shaft. Grab the shaft and try to rock it side to side. Anything more than 0.010 inches of play means replacement.
Rear Motor Bearings
The rear bearing is inside the motor housing supporting the armature shaft. This one fails from contamination or just age. You'll hear the grinding from inside the motor body, and it won't change much with bowl load. I've seen motors run for months with a failing rear bearing before they finally seize. Don't let it get that far. A seized bearing can damage the armature, turning a $140 bearing job into a $780 motor rebuild.
To test the rear bearing, disconnect power and remove the motor cover. Spin the motor shaft by hand. It should turn smoothly with consistent resistance. Any roughness, clicking, or tight spots means bearing replacement. On 1/2 HP motors, expect to spend 1.5 hours on this job. On 1 HP and larger, figure 2-2.5 hours because you're pulling the whole motor assembly.
Step-by-Step Diagnostic Procedure
Here's the exact procedure I use in the field. This takes about 20 minutes if you're methodical.
- Safety first: Lock out power at the breaker, not just the switch. Tag it. I've seen mixers kick on during diagnosis.
- Run test (if safe): Before you disconnect power, run the mixer empty through all speeds. Note when the grinding is loudest. Does it change with speed? Does it happen at all speeds or just under load?
- Hand-turn test: With power locked out, remove the bowl and agitator. Manually rotate the agitator shaft. You should feel smooth, even resistance. Any grinding, clicking, or tight spots tell you where to look.
- Shaft play test: Check for play in the agitator shaft. Up-and-down play (more than 1/8 inch) indicates planetary wear. Side-to-side play indicates bearing wear.
- Visual inspection: Remove the planetary cover. Look for metal particles in the grease, scored gears, or broken teeth. Check grease color. Black or gray grease means metal contamination.
- Motor inspection: Remove motor cover. Look for metal shavings near bearings. Check worm gear condition. The worm should be smooth with no pitting or wear grooves.
When to call a tech: If you see metal contamination in the planetary grease or if the worm gear shows wear, call us at (714) 598-2370. These repairs require specific torque specs and gear timing. A mistake here can destroy a $1,200 gearbox.
Document what you find with photos. If you're calling a service company, pictures of the gear condition help us bring the right parts first trip.
Hobart-Specific Grinding Noise Issues
Hobart mixers have a few model-specific issues I see repeatedly. The A200 and A200T series have a known problem with the worm gear retaining pin. This pin keeps the worm gear aligned on the motor shaft. When it loosens or shears, the worm gear moves axially and grinds against the housing. You'll hear a loud metallic grinding that sounds like the mixer is eating itself.
Check for this by removing the motor cover and looking at the worm gear position. There should be 0.040-0.060 inches clearance between the worm gear face and the housing. If the gear is touching or if you see bright wear marks on the housing, the retaining pin has failed. Part number 00-124036-00002 for the pin, about $18. But if it's been grinding, you need a new worm gear ($220-$280) and possibly a new housing if it's scored.
Legacy and Legacy+ Models
The Legacy series (HL200, HL300, HL400) uses a different planetary design with needle bearings instead of bronze bushings. These needle bearings fail suddenly, not gradually. You'll hear normal operation one day, then catastrophic grinding the next. When needle bearings fail, they shed metal into the whole planetary assembly. I've never saved a planetary after needle bearing failure. It's always full replacement, $580-$920 depending on size.
The Legacy+ models have a sealed planetary that's not serviceable. Hobart sells it as a complete assembly only. If you open it up and break the seal, you void any remaining warranty. These units will show grinding noise around year 10-12 in high-volume operations. Budget $680-$840 for the planetary assembly.
For all Hobart models, we maintain complete parts inventory for same-day repair. See our Hobart equipment repair page for model-specific information.
Repair vs Replace: The Real Numbers
This is the conversation I have with operators weekly. Here's how I evaluate it, with actual numbers from Southern California market rates.
| Issue | Parts Cost | Labor Cost | Total Repair | Decision Point |
|---|---|---|---|---|
| Planetary assembly only | $380-$620 | $280-$420 | $660-$1,040 | Repair if motor good |
| Front bearing | $45-$85 | $180-$240 | $225-$325 | Always repair |
| Planetary + worm gear | $600-$840 | $350-$480 | $950-$1,320 | Consider replacement if mixer is 15+ years old |
| Complete gearbox | $1,200-$1,800 | $420-$580 | $1,620-$2,380 | Usually replace mixer |
A new Hobart A200 runs $4,200-$4,800. A refurbished unit costs $2,400-$3,200. If your repair estimate exceeds $1,500 and the mixer is over 12 years old, I'm honest with customers: consider replacement. You're throwing money at a machine that will have other age-related failures soon.
What You Can Fix Yourself
If you have mechanical aptitude and the right tools, you can handle bearing replacement and planetary inspection yourself. You need a torque wrench, gear pullers, and patience. The factory service manual (available from Hobart) has all the specs. Budget a full day for your first planetary job.
What you should not attempt: worm gear replacement or timing, motor rebuilds, or electrical diagnosis. The worm gear must be timed to the planetary, and if you get it wrong, you'll strip everything. I've repaired several mixers that owner-operators damaged trying to save money on a $400 repair, turning it into a $2,000 disaster.
For complex repairs: Superior Service maintains 90% first-time fix rate because we stock the right parts and we've done these jobs thousands of times. Call (714) 598-2370 for same-day diagnosis in Orange County and surrounding areas.
Prevention and Maintenance Schedule
Most grinding noise failures are preventable with proper maintenance. Here's the schedule I give every customer, based on usage level.
Monthly Tasks (All Operations)
- Wipe down the mixer head and bowl-lift area. Flour and sugar dust work their way into seals.
- Check agitator shaft for excessive play. More than 1/8 inch vertical movement needs attention.
- Listen for any new noises. Catch problems early before they cascade.
Every Six Months (High-Volume Operations)
- Remove planetary cover and inspect grease condition. Should be clean, tan or amber colored.
- Check for any metal particles in grease. Even fine particles mean wear is starting.
- Verify all mounting bolts are tight to factory torque specs.
Annual Service (All Operations)
- Complete planetary grease replacement. Remove old grease, inspect all gears, repack with Hobart-approved lubricant (Lubriplate 630-AA or equivalent).
- Inspect front bearing for wear or roughness.
- Check motor brushes if applicable (older models). Replace at 1/4 inch or less.
- Verify all electrical connections are tight and show no signs of heating.
Grease Specifications Matter
Use only Hobart-approved grease or exact equivalents. I've seen operators use automotive grease or whatever's on the shelf. Wrong grease breaks down under the load and temperature cycles in a mixer planetary. It turns into a black sludge that provides zero lubrication. The approved greases are formulated for high-pressure, low-speed gear applications with food-safe properties.
A tube of proper planetary grease costs $28-$35. A planetary assembly costs $380-$620. Do the math. Don't cheap out on lubrication.
For operations running dough or other heavy loads, consider moving to a four-month grease inspection cycle instead of six. The extra load accelerates grease breakdown. I have bakery clients who repack planetaries every eight months because they run 12-14 hours daily with stiff dough. Their mixers last 15-20 years because they stay ahead of wear.