How to Install Disc Harrow Blades — Step-by-Step

Replacing a full set of disc harrow blades yourself is a full weekend for someone with basic mechanical skill and the right tools. Doing it at the dealer will cost $600-$1,500 in labor on top of the blade cost. The work isn't complicated, but there are three or four spots where getting it wrong will destroy the blades or the bearings within the first season. Here's the walkthrough.

Tools you need

  • Torque wrench that reads to at least 500 ft-lb (rent one if you don't have it)
  • 1-1/2" to 2" socket set (matches your gang bolt size)
  • Hydraulic floor jack + jack stands rated for the tractor + harrow weight
  • Bar clamps or a persuader bar for holding the gang while you loosen the nut
  • Anti-seize compound
  • Bearing grease
  • Fresh gang bolt (recommended — old bolts should be replaced after 2-3 blade changes)

Step 1: Set the machine up on stands

Pull the harrow into the shop or a level area. Lift the wing frames and set them on jack stands so the gangs are off the ground and can rotate freely. Never work under a harrow supported only by hydraulics.

Step 2: Remove the gang from the machine

Unbolt the gang from the frame. Each gang typically has 4 or 6 bolts holding the axle-end bearings to the frame. Support the gang on a rolling cart or straps as you drop the last bolts — a full gang can weigh 500-800 lbs.

Step 3: Loosen the gang bolt

The gang bolt runs through the center of the axle, threaded with a large nut on one end. Clamp the gang to prevent it from spinning and break the nut loose. This is often the hardest single step — the nut has been under 300-500 ft-lb of torque for years and is usually rusted. Impact tools help. Heat helps if it's really stuck.

Step 4: Slide the blades and spacers off the axle

Once the nut is off, the whole stack (end cap, spacer, blade, spacer, blade, spacer, blade... end cap) slides off. Lay each piece out on the floor in the order they came off. This matters — you'll want to reassemble in the same order, with spacers between the same positions.

Step 5: Inspect what came off

  • Bearings: Rock them by hand. Any slop, roughness, or dragging = replace. If you're here, replacing bearings is cheap.
  • Spacers: Look for wear grooves where they meet the blades. Deep grooves = replace.
  • Axle: Sight down the length. Any bend, gouge, or deep wear on the square corners = the axle needs work.
  • Gang bolt: Check the threads and shank for stretching. If the shank has a visible "necked" area, replace the bolt.

Step 6: Slide new blades on in the correct order

Blades stack: end cap, spacer, blade (concave-side facing correctly), spacer, blade... alternating each blade's concavity. On a tandem disc gang, all blades face the same direction — same concave side. On an offset gang, the two halves of the gang face opposite directions.

The convention for tandem discs: All blades on the left half of the machine face concave-right. All blades on the right half face concave-left. This throws soil toward the center on the front gang and outward on the rear gang.

If in doubt, match the direction the old blades came off. Take photos before you disassemble.

Not sure it fits your machine? Text a photo of your old blade to 515-686-5575 — we'll cross-check the diameter, thickness, and axle-hole shape against our catalog before you order. Same-day ship on orders placed by 12pm CT.

Step 7: Anti-seize and torque

Apply anti-seize compound to the axle threads before you re-install the nut. Torque per manufacturer spec — commonly 300-450 ft-lb for 1-1/4" gang bolts, 350-500 for 1-1/2". Under-torqued nuts loosen in the field. Over-torqued nuts stretch the bolt and fail early.

Step 8: Reinstall the gang on the frame

Lift the gang back into position. Grease the frame bearings before bolting up. Torque frame bolts per spec.

Step 9: Test-run the gang

Before hitting the field, spin the gang by hand. It should turn smoothly with no wobble, no scraping, no side-play. Any of those = pull it back apart and figure out what's wrong.

Common mistakes that ruin new blades

  1. Mixing new and old blades on the same gang. Different diameters stress the gang bolt. Replace by gang or better yet by machine.
  2. Not replacing gang bearings. Worn bearings let the axle wobble. The new blades wear unevenly. See our when-to-replace guide.
  3. Wrong torque on the gang bolt. Get a torque wrench. Not a guess.
  4. Blades installed with wrong concavity direction. The machine won't track straight and blades wear one side only.
  5. Forgetting anti-seize. The next time you replace blades, you'll be fighting the rusted-on nut for hours.

Shop the blades and parts

Frequently Asked Questions

How long does a full disc harrow blade change take?
For a 36-blade tandem disc, expect 6-10 hours if you're doing it solo with basic tools. Two people cuts it to 4-6 hours. Add 2-3 hours if you're also replacing gang bearings.
Do I need to replace the gang bearings when I replace blades?
Not required, but strongly recommended if you've got the gang apart. Bearings are cheap relative to blades, and worn bearings will make the new blades wear unevenly.
What torque do I use on the gang bolt?
Manufacturer spec. Rough range: 300-450 ft-lb for 1-1/4" gang bolts, 350-500 for 1-1/2". Use a real torque wrench — this isn't a "feel it" job.
Can I install disc blades with just an impact wrench?
For loosening the old nut, yes. For torquing the new nut, no — you need a torque wrench to hit the spec. Impacts don't control torque; they just spin until they can't.
What if the gang bolt won't come loose?
Heat + penetrating oil + impact. If it still won't move, an air hammer or a cheater bar with a pipe extension. Last resort: cut it off with a sawzall — but plan to replace the bolt anyway, so cutting it is not a disaster.