How to Replace Rotary Slasher Blades, Step by Step

Replace slasher blades in complete sets, never individually, and always fit new pins or split pins rather than reusing old ones. Replacing a single worn blade leaves the carrier out of balance, and an unbalanced carrier spinning at working speed will destroy gearbox seals and bearings faster than the blades ever wore out.

The job itself takes under an hour with the right tools.

When blades need replacing

Look for any of these:

• The leading edge is rounded rather than sharp, and the machine is tearing material instead of cutting it
• Visible cracks anywhere on the blade, particularly around the pin hole
• The pin hole has gone oval — this is a replacement, not a sharpening job
• A chunk missing from the blade, which means the set is out of balance immediately
• The blade no longer swings freely on its pin

A blade that has hit something hard should be inspected even if it looks fine. Cracks around the pin hole are easy to miss and they fail suddenly.

Safety first — this part is not optional

A slasher stores a serious amount of energy and the blades keep spinning after the PTO is disengaged, sometimes for a minute or more.

1. Park on firm, level ground.
2. Disengage the PTO and switch the tractor off. Remove the key and take it with you.
3. Wait for the blades to stop completely. Look, do not assume.
4. Disconnect the PTO shaft from the tractor.
5. Lower the slasher fully to the ground, or if you need it raised to work underneath, support it on properly rated stands or solid blocking. Never rely on hydraulics alone — a hose or valve can fail and the machine will come down.
6. Wear gloves and eye protection. Old blades throw rust and grit when you hit them.

Tools you will need

• Socket set and a long breaker bar, or an impact wrench
• Penetrating oil
• Hammer and a drift or punch
• Wire brush
• Torque wrench
• New blades, new pins or bolts, and new split pins
• Grease

The steps

1. Clean around the fixings. Wire brush the pin or bolt head and the area around it. Most of the difficulty in this job comes from grass, mud and rust packed around the fixing.

2. Apply penetrating oil and give it ten minutes. It is worth the wait.

3. Remove the split pin and nut. On most machines each blade is held by a pin or bolt through the blade carrier, secured with a castle nut and split pin, or a locknut. Discard the split pin — never reuse one.

4. Drive the pin out. Use a drift and hammer from the side that clears. If it is seized, more penetrating oil and patience beats more force; hitting the carrier hard enough to move a seized pin can distort it.

5. Remove the blade and set it aside. Do the same for the others, working around the carrier.

6. Inspect the blade carrier before fitting anything new. With the blades off you can see everything properly. Check for cracks radiating from the pin holes, elongated pin holes, wear or thinning on the underside, and any wobble in the carrier itself. A carrier that moves on the gearbox output shaft, or shows play when you rock it, needs attention before the machine runs again.

7. Check the gearbox while you are there. Look for oil weeping around the output shaft seal and check the oil level. A seal that has started leaking will empty a gearbox faster than you expect.

8. Fit the new blades. Orientation matters — the sharpened edge must lead in the direction of rotation. Note which way the carrier turns before you start, or check the arrow usually cast or stamped on the deck. Fitting blades backwards is a surprisingly common mistake and the machine will barely cut.

9. Fit new pins and nuts, and torque them to specification. Then check that each blade swings freely by hand. This is the single most important check in the job. Blades must be able to pivot back on impact. A blade pinched tight against the carrier turns every obstacle into a shock load straight into the gearbox.

10. Fit new split pins and spread the legs properly.

11. Grease everything on the schedule for your machine, including the PTO shaft and the tailwheel hub.

After fitting

Reconnect the PTO shaft, start the tractor, and bring the PTO up to speed slowly with the machine lowered and everyone standing clear. Listen and feel for vibration. A smooth machine sounds smooth. If there is any noticeable shake, stop immediately — that is almost always an imbalance from mismatched blade weights or a blade that is not swinging freely.

Run for a few minutes, then shut down and recheck the torque on all the fixings. Recheck again after the first hour of cutting. New fixings bed in and loosen.

Sharpening versus replacing

Blades can be sharpened, within limits:

• Sharpen only the leading edge, following the original angle
• Remove the same amount of material from every blade in the set, or you have created an imbalance
• Do not grind to a fine razor edge — it will chip on the first stone
• Do not overheat the steel while grinding; if it changes colour you have softened it
• Once a blade is significantly thinned, or the pin hole has worn, replace it

Blades are inexpensive relative to the gearbox they protect. When in doubt, replace the set.

How often

There is no fixed interval; it depends entirely on what you cut and what you hit. Reasonable practice is to inspect blades and fixings at the start of each season, after any significant impact, and roughly every 40 to 50 working hours in rough conditions.

If you need blades, pins or a carrier for your machine, send us the model and we will confirm what fits.