Small Engines (Lawn Mowers, etc.): Transmission, belt pulley, vee belt

Question
QUESTION: Hello - I have an older Simplicity 6516 tractor with a hydro transmission.  Over the past month it is going slower and slower up the small incline in my yard.  Engine rpm's remain the same but tractor slows way down.  Drive belt from engine to trans was replaced in August.  Is my transmission going bad?  Many thanks -

ANSWER: Hi Bill  

can you give me model and make  of  hydro transmission unit  , there should be a tag or sticker on it - but if all inputs are good and no  drag or brake bind etc  , sounds like it may be either very low on oil ( possibly cavitating)  or the pump  and or hydraulic motor in the hydro have worn out  hence the slow speed  


let me know  make and model of hydro unit  please

cheers paul

---------- FOLLOW-UP ----------

QUESTION: OK.  Simplicity 1691263. Transaxle group.  Fluid is full but has not been changed recently.  Do not see exact make and model of hydro trans unit.  Here is a diagram:  http://www.partstree.com/parts/?lc=simplicity&mn=1691263+-+6516H%2C+16HP+Hydro&d

Answer
Hi Bill  

I would try  changing oil and filter on the unit 1st , then provided  all inputs from  vee belt, pulley etc are ok   and unit has correct fluid and quantity  but is still not moving properly  it may well be the hydro pump / motor unit  inside the transmission

be sure  trans belt has good tension it  and brake system is not dragging/binding
be sure the link from foot or hand control lever to hydro unit is moving the pump swash plate  that goes into the transmission  from the side  ?

if all is good  , then only be the transmission playing up   !!!


see what you can find  , let me know  


cheers  paul  

update  ----has the oil and oil filter been replaced, and unit purged of any air ?incase its dropped its additive pack.

have you checked nothing is restricting flow of oil  from oil tank to pump ie  blocked / restricted tank screen ?

note  be sure that the bypass is not partialy disengaged  or is stuck open
its possible releif valve may be stuck open or sticking

these units have a eaton cam ring  type pump on the top side of trans , and a l/h and r/h eaton wheel motor / with differential gear assy

low flow of oil through system maybe causing  low speed even though input shaft speed is good to pump ,   in hydraulic terms  flow of oil relates  to speed  and the pressure relates to torque  both are quite closely related

as stated earlier  simple things 1st then  if still not responding , decision weather or not to relief valve ,eaton pump , wheel motors.

let me know if anything helps  

cheers paul