Outdoor Power Equipment and Small Engines - Deere L 118 slows down after hours of use

I recently bought a John Deere L-118 automatic lawn mower that was run hard but well maintained. After a few hours of use it doesn't move as fast as when it is cold. The motor stays the same RPM but the mower drive speed slows down. It has a new drive belt and pulley so it isn't slipping. Could there be a problem in the trans? Do they have a filter that can be changed like a car trans? I am not familiar with these machines but have fixed many riding mowers over the years. This is the first automatic I have dealt with. Any sugestions? Thanks.

I believe that the hydro tranny will be a Tuff Torq brand. I don't have enough experience with them to advise you well so stay tuned for Cheese, the other moderator, and others who may. I'd suggest tufftorq.com for any possible service info on their site, in the mean time.

Look at the top of the tranny, and I'll bet there is a lot of debris and clippings piled on it. This tranny has cooling fins like an engine, and a fan on the input shaft to blow through these fins. If these fins are covered with clippings, the tranny runs hot and the oil characteristics change, and the pump can cavitate. Usually cleaning it fixes the problem. Check the plastic fan for broken fins. If they are missing, replace it.

Thanks, I will check into this.