Small Engines (Lawn Mowers, etc.): hydro on riding mower, hydrogear

Question
QUESTION: What would cause the hydrostatic  to quit working after about five minutes on a Toro riding mower

ANSWER: Can you give me some more info on this?  About how many hours does it have on it or how old is it?  Is there any unusual noise?  Will it work in reverse? What is the make, model and serial number off of the transaxle itself?  Thanks, PK.

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QUESTION: Here is what i found out.
Unsure of hours. 1995 is the year. No unusual noises. Works in forward and reverse for a couple minutes. Hydro Gear 92-9790 4170T4020

Answer
The common causes would be a slipping belt, the transaxle overheating, a sticking brake, low oil and maybe the bypass valve somehow engaging.

I would check the belt first.  Then I would clean the transaxle and make sure the fan is in one piece and functioning.  If the mower will roll easily with the bypass valve engaged and not roll with it released, then that would rule out the brake and valve probably.  Also make sure all linkage is firmly attached and moving through it's complete range.

To check the oil, if yours doesn't have an external resevoir or check plug, then you can remove the breather and measure down from there.  The level should be from an inch to two inches from the top of the case.

Thanks and let me know if you have any questions.  PK.