Why Do Snow Blower Shear Pins Break?

The most frequent question we get this time of year is why shear pins keep breaking. Here's everything you ever wanted to know about shear pins (and then some).

What are shear pins?

The short answer is they are hard metal pins commonly used in snowblower augers that are designed to break if ice or rocks get wedged between the auger and the housing.  They break so the auger shaft and augers can spin freely and prevent bending an auger, stripping the gears or damaging the engine.

How are they used?

The metal shear pin slides through the auger axle hub and locks the hub in place with the auger axle drive shaft. They may be fastened by locknuts or cotter pins, and some shear pins sit in sleeves or include spacers, depending on the brand.  All two-stage snowblowers have at least one shear pin on each side of the auger gear case (and sometimes 2 on each side)  and they are often found on single-stage snowblowers too.

Why should I care?

If you break a shear pin, your auger won't turn, and your snowblower won't blow snow!  So a tiny broken part can have big repercussions.

Why do they break most often in February?

This one is tougher - weather across Canada varies, but generally, snow is wetter, heavier and icier in January and February and when we get melt and freeze cycles, rocks are exposed and ice builds up more frequently. Anything caught between the auger and housing can cause shear pin breakage, including heavy snow build-up from fast passes.

And if you changed your shear pins during your pre-season tune-up, they might be getting stressed from usage by this time of year.

How do I know if a shear pin is broken?

If you suspect a shear bolt is broken, stop the engine, remove the key, wait for all moving parts to stop, and disconnect the spark plug wire from the engine.  When safe, tip the snowblower back and inspect the augers.  If you don't see the shear pin head or locknut and you can manually spin the auger along the shaft, you have a broken shear pin.

Generally, a shear pin replacement is considered a common maintenance task for a homeowner, but if you are concerned about safety or your ability to do-it-yourself, bring it to an expert!  DR Mower Parts in Calgary has teamed up with Rupert's Repair for maintenance and repairs, or your local repair shop should be able to quickly and easily replace shear pins.

How do I replace a shear pin?

A broken shear pin should come out easily.  They often fall out when they break.  If a piece gets stuck you might need to use a punch and hammer to tap it out.  

Once the broken one is gone, replace the unbroken one(s) too! You can save the unbroken one for a spare, but you want as little down-time as possible.  It's best to replace with all the shear pins at once.

Move the auger shaft until you can align with the auger hub holes and slide the replacement shear pin into the hole. Fasten with the nut or cotter pin made for your unit. Tighten until snug.  Do not overtighten as it can stress the pin and cause early failure. 

Once the shear pin is installed, rotate the auger by hand to confirm the pin is secure. If the auger doesn't rotate freely along the auger shaft, you're ready to restart your snowblower and continue clearing.

1501216MA Shear Pins with Spacers on some Craftsman models

Don't forget to reconnect your sparkplug wire and replace the key, restart the engine and engage the auger lever to test.  Blowing snow?  Good to go!

Can I use any bolt?

A shear pin is different from a regular bolt as it is designed to "shear" or break under load.  They have a weak point that snaps if a jam happens between the auger and housing.  

Always use the right size shear pin for your snowblower. Check the service parts section of your owner's manual to identify the correct part number for your unit. You will need a pin that shears at the proper torque. If you use a pin that can handle more torque than your machine, you risk causing extensive damage to your snowblower.

Briggs & Stratton 707555 Shear Pin Kit with Locknuts

For the techies - Torque varies by unit but is approximately 20-30 ft lbs. Confirm torque in your manual. A "shear bolt" by grade doesn't exist.  A shear pin is created by cutting relief grooves (a shear point) in a pin which is hard enough to maintain auger rotation, yet soft enough to shear if the auger is prevented from rotating. Shear pins are available in stainless steel (A2), BZP (Bright Zinc Plate) or with a galvanized finish and in a range of sizes, usually specialized by the manufacturer. So they are generally are not interchangeable amongst brands (although they may be interchangeable amongst similar sized models within a brand). You may read that a shear pin is the same as a grade 2 or 5 or 8 bolt, and there is lots of info out there,  but I urge you to check out this post with a technical breakdown on calculating shear strength  (leaving our site)

How do I figure out which shear pin I need?

The best way to find the right part for your unit is to check your owner's manual.  If you don't have one, we have 2000+ free manuals available for safe download on our website. Simply search by your model number.  Or email parts@drmower.ca, call our parts specialists 1-877-531-2873 toll free, text or call local (587) 329-6642, or check out the chat function on our website

Replacement shear pins and other snow blower parts can be ordered in our online parts store or are available for pickup at our Calgary warehouse.

Avoiding Breakage

The best way to avoid shear pin breakage is to ensure you are not hitting rocks or ice balls! No seriously, keeping your auger free of buildup is the #1 way to stop from breaking shear pins. Other things to check:

• Are you using the right shear pin for your unit?  They are very much brand-specific, different sizes, different tensile strength and have different fasteners.  As noted above, some have sleeves or spacers.  Check your manual or contact us for help!
• Are the shear pins installed correctly?  Don't over-tighten them.  Check the torque specs in your manual
• Is your auger clean and lubricated?  If it's rusty, snow can stick easier and ice can build up.  Clean and use a metal lubricant 
• Check your auger cable.  Is it the right part for your unit?  Worn or functioning properly?
• Check the drive cable. Is it causing a surge on start-up or dragging?
• Is your engine running properly?  A rough running engine could impact the drive system and cause additional stress on the auger
• Do you have proper air in the tires? A good scraper bar?  Skid shoes properly adjusted? Make sure your snowblower is sitting how it's supposed to and gliding over the snow and not digging down.  If a single-state snowblower, check the flights aren't worn
• Before storing the snowblower, always run it on a clear surface to clear the auger of any remaining snow and clear the area around the chute and the housing
• After each use, make sure all screws and bolts are snug. Look for broken or worn pieces and replace them right away
• If none of this helps, take your unit into a repair shop.  They can check if the auger is bent, there is a problem with the gear box or other more serious issues
• And remember, in the industry, shear pins are considered disposable parts.  They are made to break and should be replaced regularly.  Keep some extras on-hand so replacement is quick and easy

Final Notes

Just to make it more difficult, while I've been outlining snow blower auger shear pins, they are also found in snowblower impellers, on lawn tractors, and other lawn and garden implements, as well as have industrial uses.  We carry shear pins, locknuts and cotter pins, and shear pin kits for most makes and models.  If you can't find it in our online store, please contact us as we can likely get it.

While shear pins are small, relatively inexpensive parts, keep in mind we have free shipping on all overs over $99 for the month of February, so add a pack to your order or stock up!

Free shipping in February on orders over $99 - no discount codes needed!

...and the fine print

Warning: Undertaking repairs or maintenance to outdoor power equipment or any kind of equipment can be hazardous. Should you choose to undertake repairs or maintenance, you are assuming the risk of injury to your person or property. In an effort to reduce the risk, use the proper tools and safety equipment and follow all instructions. Do not proceed until you are confident that you understand all of the steps and are capable of completing the repair. Some repairs or maintenance, however, should only be performed by a qualified technician. The information provided in this blog is for informational purposes only. We are not responsible for any damage that may occur as a result of following these instructions.

 If in doubt, call an expert!

Stay safe and warm out there!