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Small Engines (Lawn Mowers, etc.)/Loss of hydrostatic transmission power


I have an Ariens Sierra 1540H mower (Model # 936026, SN 000850) with a Hydro-gear 325-0750 transmission that recently lost power to climb hills even though there is no loss of engine or cutting power or cutting power.  Some power continues to be transmitted to the wheels so that the mower will travel on a level surface, but it will no longer climb even a gradual grade.

The drive belt appears to be OK.  After reviewing an online recommendation, I drained the unit and refilled it with new 20W-50 oil as indicated by the mower service manual.  That made no difference in the mower's operation, so my next repair attempt was to remove the transmission from the mower, open it, and inspect it's major components.  They all appear to be in perfect condition.  I replaced the filter, reassembled the unit according to the service manual directions, and replaced it in the mower.  Again, there was no improvement in the performance.

Other than the transmission, the mower is in top condition.  Any recommendations you have would be greatly appreciated.

Some of the hydro parts may just be wore causing it to lose pressure.  Did you purge the trans after filling oil?

Generic purging procedure.
Place the "free wheeling" lever into free wheel mode (transmission will not drive this way).
Sit in seat and start engine with brake/clutch pedal down, and the trans lever in neutral.
With engine at idle RPM, let the brake/clutch pedal up.
Move the trans control lever to FULL FORWARD and hold it there for a minimum of 5 seconds.
Move the trans lever to FULL REVERSE and hold it there for a minimum of 5 seconds.
Repeat the Full F to Full R at least 3 times.
Stop the engine and move the free wheel control to the engaged position, make certain it fully engages.

Did you fill with 81 oz. of oil?  


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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