Ive got a bobcat 853 1995 and last year I had to put a new pump in it and had the drive motors re surfaced. Now after about fifteen minutes of use, the power drops off and the steering goes all wonky. The hydraulic fluid does not seem to be too hot. Also, the belt tensioner is new and is an upgraded part that I installed myself. They told me it had to go in the opposite way of the old one, but I could only get it to go in the same way as the old one. Bobcat came out and checked tension and that is OK. The machine spent a few months at bobcat of edmonton last year and they dumped about $12000 worth of hours into it with no results and I just can not afford for them to do any more diagnostics, nor do I have any faith in them for being a quality repair shop. Any help would be very much appreciated.
After 15 minutes, Hyd. fluid reaches opperating temp, thus lower viscosity. At this point the much thinner fluid might be escaping out the drive motors rotating groups due to a bad overhaul. It would go out the case drain in drive motor ( smallest line) When you pulled the drive motors for overhaul, did you bleed the air out of them upon installation? Without being there, the best advice I have is to pull the motor again, take it to a Hyd. shop and have it bench tested. Getting the air out of hydrostatic drives is a must.