I just picked up an 863G with 2-speed. Trying to figure out where to start with the drive system. When operating on an incline there is no hydrostatic holdback. It rolls like it is in neutral on any incline as well as having jerky engagement of the drive. Fluid is full and bucket operates with no issues. Is this is final drive issue in both motors or a control valve issue.
After reading through the service manual several times I think I found the issue. The two-speed drive uses a spring actuated brake within the drive motor for the parking brake. It is released via a solenoid that applies hydraulic pressure. Once I figured this out I went to check the solenoid and spool. To my surprise the brake spool and solenoid were completely missing and a plug was installed. Parts are currently on order.
That doesn't sound right???? the parking brake is only for parking and shouldn't have any effect when operating the motors... Hopefully one of the bobcat experts will chime in soon...
That was my thoughts and experience with single speed drives as well. The two-speed drive has no hydro-static braking by design so it actually has a brake section that resembles a transmission clutch pack. it is controlled electrically and released via the micro switches on the control arms and the parking brake switch. With the brake spool removed and capped it was always released when the motor is running. This is a new to me machine that I'm finding lots of redneck engineering on. The fuel cutoff solenoid was bypassed with a wire to the cab and an alligator clip. To get an idea of the former owner I bought it from read this, https://www.webcenter11.com/content...s-dumpsters-from-transfer-site-508709161.html
Interesting... I have never worked on a two speed like that one... so both motors were bypassed eh'? Makes you wonder if something is bad inside the motor/gbox the reason they removed the other parts....
Finally fixed this. Long story short their is a makeup solenoid valve that opens for high speed operation. The spool was broken internally and stuck open leaving the drive motors in a bypass state. For now I just capped all the hoses and disabled the two speed while I order a new spool.