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Small Engines (Lawn Mowers, etc.)/Mower will not move fwd or back


Hi Eric
I have a Murray I bought new in ’92. 12.5hp/40”, model 40631A.
Problem started when right rear tire went flat while mowing;  tire was off the rim and rim WAS spinning. Had tire repaired, put it back on and now mower will not move forward or backward. Owners manual says it is either motion drive belt or clutch adjustment. Drive belt is on pulleys, appears to be tight; I adjusted clutch per the manual. Jacked up rear end and removed wheels….left rear axle turns while in forward gear and in reverse, right rear axle does not turn in forward or in reverse. BUT, when I removed the repaired RR tire, I noticed axle key was missing and there were metal  shavings inside the key groves on both the axle and inside the wheel. So I don’t know if the key sheared or if the key fell out while I was replacing the repaired flat tire. I replaced the repaired tire in middle of yard, raining, had mower jacked up without jackstands so it was wobbly and I got in a hurry. So I may have lost the key instead of it shearing. I have purchased a new axle key but have not installed it yet because I did not know if maybe I have some other problem or if I just need to put the axle key back in to solve my problem. Called 3 major repair shops(nashville, tn) and none had a Murray axle key; but one of their technicians happened to have one just my size in his tool box. So I don’t want to take the chance on shearing this one until I know what I am doing.
Thanks so much, Eric.

Pretty common to loose the key and it will cause your symptom.  Should have been a standard 1/4 inch square key sold at most any auto parts and hardware stores.  We just use the 1 foot length square key stock and cut to the length needed.  If the axle or wheel key way are wore you may want to get a square key stock (1 foot) and cut you own key...just longer so there is more material for the axle/wheel.

I'd recommend using some antiseize compound on the axle and inside the rim/wheel.  I've many a riders where the wheel was rust frozen to the axle preventing the wheel from being removed.  I've busted axles, keys, and even made some special tools for removing rusted wheels.  Worst case we had remove the tire from the rim and cut to wheel off the axle with a grinder...not that had but pretty expensive when you have to replace the wheel and tire.

Install the tire/wheel first, then align the key way and install the key and wheel retaining clip.

Let me know if replacing the key fixes the problem.

Small Engines (Lawn Mowers, etc.)

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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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