Hi Martin. I guess you may have solved the problem or got a new machine. I have just removed my transmission which is fitted to my Viking mower. My experience is the same as yours. Running out of steam on a slope and generally slow. I rang around a few mower shops and they all say it is past it's use by date. My mower is 9 years old now. Has been a dog from the start. I have just managed to get the cutting deck sorted out with a few of my own very successful modifications and now the transmissions throws in the towel.
I have just removed it and replaced the oil with a synthetic 15/50.. I have received mixed advice about the oil. Some say a synthetic 20/50, others a straight SAE 30.. The Tecumseh site says gear oil 85/140. I don't think an oil top up is the answer for me as the amount I took out is about the same volume as what I have put back in. I guess I could split the box and see if there is anything very obvious inside or just put it back in the mower and hope for the best.
Not too much on the internet about fixing them. Now that I have the numbers I might have a better chance..
All the best.
David.
David
December 2010
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