If you are getting 5,000 PSI i do believe the pump is working correctly.I just swapped the servos. The problem, however, remained on the left side. Today, I discovered that the left drive motor had no seal on the shaft that goes through the resevoir wall to connect up with the main drive sprocket. When I took it off all there was, was two large washers and a bunch of form a gasket. I'm assuming the previous owner just made his own seal. I'm suprised it lasted so long though, or I guess that's why it felt weaker on that side. Anyway, I put everything back together, with a new seal, thinking I was Mr. fix-it and nothing. Still does not move. I put the pressure gauge back on the out-put line, #19 if you're looking at figure 096 on the new holland web site, and removed the servo to work the control by hand. when no pressure was applied my reading now comes up ZERO. When I grabbed the control arm, directly connected to the rear piston pump, and worked it myself the pump got a mind of its own and shot up to at least 5000 psi. I dove out of the loader thinking my gauge was going to explode...but then the machine stalled out. Still the wheels did not move on the left side. Tomorrow, I'll see if the hoses will reach to hook up to the right side motor with the rear pump, or the forward piston pump with the left side motor, if those hoses will reach. I can't see that #17 is blocked (same figure), because i had it completely unhooked and blew through it, thinking there may be a plug. While I was re-testing though fluid would come out of #19 from the motor not hard and fast but at a steady pace.
Be very careful installing pressure gauges on the hydrostats, 5,000 PSI is more than enough to kill you. Its normal for the machine to stall as there is no where for the fluid to escape, thats why when testing these sort of things they use a restricting valve so the fluid is still moving but you can control the pressure build up. They say to bring the pressure up slowly and not to exceed 5,000 PSI.
I would say it is indeed the motor, i still think the best way is to swap motors if you can, then you will know for sure.
If you are getting constant by-pass like that there has to be something broken, if it has worn, it will by-pass slowly but it will still have drive power. Test the *good* motor from the other side on the bad side and if it works, pull the dead motor down and have a look. You can't cause more damage if it is already broken.
Thats what i would do at least.
Remember, be carefull with those pressures, i can't stress it enough! if a hose split you could get a jet of oil that can cut you badly.