I just got this machine it has 1400 hrs. and after operating it for 15 min. I felt pretty sure it needed the left side drive motor rebuilt. The lift and bucket worked fine but, it wouldn't steer (skid) sharp to the left and when I took the cover off the chain box, it was almost to the top with oil (white milky oil that is). While the drive motor was being rebuilt I also replaced the leaky hydraulic oil cooler and a badly rubbed cooler hose. I also blew both out with shop air before installing. After installing the drive motor and hydraulic filter I topped off the hydro tank with 10W 30. I fired it up worked the control levers back and forth left to right and it seemed ok. The left side still didn't seem perfect and maybe even a little jerky. I took it out of the shop for more testing and while scooping up small piles of gravel. As far as the lift and bucket tilt everything was great, I moved 2 pickup loads of gravel easily. I put the loader into the pile of gravel to see if either side of the wheels would spin and neither did. I tried this a couple times and noticed it started to get hesitant and slightly weaker. It was also getting a little slower as I ran it, so I started back to the shop and on the way inside it slowed to a stop. I had to pull the levers back to reverse and then forward to creep the machine back inside. I recently got a manual and checked the charge pressure. Both sides stared out with about 120 psi. which eventually faded to nothing. My question is if the drive motor wasn't resealed correctly could it cause fluid by passing to cause all of this? Even though I know it is possible I don't even want to think I introduced trash while installing the motor. I also plan on checking the charge check valve in the relief block. Please, help me, help me...
120 charge pressure sounds too low. Did you check that before you made the motor and oil change? Record the charge pressure at high idle in neutral. Then record it at high idle with the left drive pushed forward (stall it against a tree or something immovable) and record that.......same with the right side. Make sure your hydraulic oil is warmed up. Post your pressures here afterwards.
If your LH motor was trashed just rebuilding it alone may not fix the problem. The trash from the motor would circulate in the charge pump and the main pump and could pass trash to the RH Motor. When a motor needs rebuilding in a hydrostat system it's always a good bet to check the other motor, charge pump and main pumps or you end up going in circles.
Thanks, guys for the reply! I did not check the charge pressure before removing the motor. I just noticed the issue with the left-side steering and after seeing the chain box full of oil, I felt I should start there. I went back out this morning for more test. After changing the hydraulic filter again and warming the fluid, at high idle it had 250 psi both sides. I took it outside with the gauge in the left-side charge pump test port. I dug into a bank and the gauge went from 250 to 0 psi. I put the gauge in the right-side test port, and it went from 250 to 1500-1600 psi. I also noticed right side tires would spin when I only had the right-side lever pushed forward. I also noticed the machine did not respond well to moving the left control lever. I had to feather it or use the right-side lever to inch forward it would not turn or move with only the left lever in the forward position. I also noticed towards the end of my test the gauge was around 150 psi.