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  1. #1
    New Member
    Join Date
    Mar 2012
    thibodaux, la
    craftsman dls3500

    Default Hydrostatic Transmission Slipping ???

    Ok. I own a 4.5 years old Craftsman mower with a 20 HP Briggs motor and a hydrostatic transmission manufactured by Tuff Torq (K46 model).

    The problem I had was the engine would run fine but it would lose power going to/through the transmission. It would work ok but then get progessively worse the longer I would use it. Then I would take the mower out again and the same thing would happen but it would get a little worse. I initially diagnosed the problem as being the belt was worn and must be stretching as it was warming up. I changed both the drive and blade belts and it did not correct the issue the slightest bit.

    At this point, I spoke with three mower repair shops and read everything I could find on hydrostatic transmission problems. (I can't tell you how many posts I found of similar transmission complaints) The most consistent suggestion was purging the transmission of air. I did this again and again with no help to the problem. Also, by this point the mower wheels would turn when I jacked up the back end but the mower would not move much once I put it on the ground. It seemed like the gears might be worn down and slipping once a load was put on the mower/transmission.

    So, ok - I read some more through every forum and decided to take the transmission down and open it up. Guess what, the gears looked fine with little to no where. $h!t - did I have the wrong belt? I checked again and it was correct. I was truly at a loss as to what to do.

    Alright, here is the fix I discovered. I happened to see somewhere about oil that has degraded being prone to "foam". (By the way, hydrostatic transmissions use engine oil - not transmission fluid) With that thought, I wondered about the properties of cold oil vs warm oil and also would bubbles/foam forming in the oil mimic the need to purge trapped air from the transmission. As a result, I drained all the fluid from the transmission case over about a day. I then purchased 20-50 weight synthetic oil. I chose Valvoline Racing oil as it indicated that it had a anti foam quality to it. I reinstalled the transmission and purged it of air.

    Guess what - the mower pulled like new. No $200 tranny rebuild kit. No $650 new transmission from Tuff Torq. Just two $9 quarts of oil. Some might reply that this should have been common sense but nobody anywhere connected the dots. It seems that mower repair shops don't specialize in transmission work and transmission shops don't really deal with lawnmower repairs. Good luck with whomever finds this information.

  2. #2
    Elite Member
    Join Date
    Jan 2010
    Northern, IL
    Branson 2400H, JD X540

    Default Re: Hydrostatic Transmission Slipping ???

    Yes, the heavier weight oil will help for a while and then your problem will return. These HST trannies are considered throw aways since usually rebuilding them is a bout 75-80% of the cost of a new one.

    Keep the fan blade in good shape an keep the tranny clean of oil and dirt to aide in the cooling. That is about the best you can do.
    Artificial Intelligence will never overcome natural stupidity.

    Branson 2400H MMM & FEL

    JD X540

  3. #3
    New Member
    Join Date
    May 2017
    Countach Rider

    Default Re: Hydrostatic Transmission Slipping ???

    My reverse is not engaging very well have to hold the leaver hard back to get any effect . Countax Rider quite old pre 1990 i think . Goes forward ok ..

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