Should Snowblower Auger Spin Freely?

Making great progress and then "bang" - snowblower stops blowing snow. It's a startling experience and at once you know somethings up. You are in the right place alright, I'm a mechanic and this is a common snowblower issue.

A snowblower auger should not spin freely when the auger control lever is off. A freely spinning auger is a symptom of broken shear pins. Shear pins are a fail safe feature, designed to break when the auger hits a solid object.

In this post you'll learn what shear pins are, how to diagnose their failure and how to fit new ones. I'll also point out the importance of using the correct shear pins.

Mower gas cap

Vented Gas Cap

What are Snowblower shear pins?

Shear pins are also known as shear bolts, they are metal fasteners employed to fix the auger to the auger shaft.

Shear pins come in two main flavors: bolts or pins. The bolts are obviously threaded and the pin variety uses a pin and clip to fasten. Not all snowblower auger shear pins are the same.

There are many different size shear pins, both bolts and pins.

Vented mower gas caps

Vented gas caps

What do Snowblower shear pins do?

Shear pins as you know fasten the auger to the auger shaft. The auger shaft is powered, without the pins, the auger shaft would simply turn without turning the augers. Not much use for shifting snow.

But the shear pins have another even more important function. They are designed to shear (break) when call upon.

Inertia, an object in motion carries energy. When an auger suddenly stops, that energy must be dissipated. We've all done it, we've all tried to shred a frozen newspaper.

The shear pins absorb the energy by shearing. If shear pins failed to do their job, the energy would instead be transferred into the gearbox and transmitted on to the engine. Often resulting in lots of down time and many hundreds of dollars in repairs.

How to diagnose Broken snowblower shear pins

Now you know a sheared auger pin is a good thing, otherwise you could be fixing a gearbox or worse.

Your auger assembly has as you know a separate auger each side, with it's own shear pin. Breaking both shear pins at the same time is unusual but not impossible.

Diagnosing broken shear pins is pretty easy. The main symptom is a free spinning auger.

Go ahead a place your hand on each auger in turn, they may move slightly, that's normal but should not be free to spin.

If you can spin it, your shear pin has sheared.

Symptoms of a broken shear pins include:

  • Auger spins freely
  • Snowblower not blowing snow far
  • One auger not moving when auger lever engaged
  • Snowblower not moving snow as before

How to fit new snowblower shear pins

Fitting is one of the easiest jobs you can do on a snow blower. Frankly I'm a little jealous, in my workshop I only ever seem to get the really tough jobs.

Anyhow, it is super important that we disable your snow blower before working on the business end.

It's a simple procedure, I remove the spark plug wire, just twist and pull and set to one side away from the plug. Not you're all set for working safely.

tools you'll need

To make the job move like butter you’ll need the following tools:

  • Wrench set (ratcheting would be nice)
  • Ratchet & socket and long extension
  • Hammer & punch
  • WD40
  • Grease gun
  • Hand light (over 50s)

Replacement shear pins

I can't emphasize enough how important it is to fit the correct shear pins. Sure, shear pins might look like a nut and bolt but they are chosen to suit your machine. Meaning the metal is sufficiently soft so as to shear long before kinetic energy grenade the gearbox.

Bolts are identified by their tensile strength, its the maximum force they can withstand before fracturing.

Standard (inch) and metric (mm) measurement bolts employ different markings to identify bolt strength. Most manufacturers use metric but you can expect to see plenty standard bolts too.

Standard bolts (imperial (inch)) use a grade number. Grade two (identified ironically by no markings at all on the bolt head) is the preferred grade bolt for shear pins.

An equivalent metric bolt is marked 5.6 on the head. Both bolts have a tensile strength in the 60-75,000 pounds per square inch area.

Fitting bolts graded above a grade 2 tensile strength simply means they won't shear until a greater force is applied.

Fitting bolts you may have laying around the garage is not cool. I'd be very disappointed as that would mean I didn't do my job very well.

Order new pins as per manufacturers specs, shear pins are not all the same. I have included many of the more common types together with the tools you may need to fit them, here on the "Snowblower maintenance tools page".

Shear pin replacement as follows:

  • Rotate the free spinning auger to locate the auger axle pin hole.
  • Broken pin remnants may be lodged in the axle. If so, use hammer and punch to remove. Add a little WD40 first
  • Using a grease gun pump grease into the auger grease nipple and spin auger to distribute the grease
  • Align the auger hole with the axle hole
  • Fit the new shear pin. (some augers may have a hole larger on one side, if so ensure to fit the pin with shoulder to the larger side)
  • Bolt type – Tighten shear pin (bolt) using wrench and ratchet set until it seats, then back it off. The shear pin should be free to spin
  • Pin type – Fitting the pin style is easier, push pin home and fit clip

It is important shear bolt type pins aren't tightened to the auger securely. Doing so won't allow the shear pins (bolts) to shear and could cost you a gearbox or an engine.

Now get out there and start moving snow!

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Auto Technician and Writer at Lawnmowerfixed | Website

John Cunningham is an Automotive Technician and writer on Lawnmowerfixed.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write "How to" articles that help fellow gear-heads with all aspects of mechanical repairs, from lawn mowers to classic cars.