Some slide outs have a brake and some don't. Would check the manual that came with the RV and see what they have to say about manual operation. The last time that I had slide problems, it was the motor had gone bad. How long has the slide been in the extended position? If you can see the mechanism under the slide, the hydraulic system will have a cylinder with a rod coming out of the middle of one end attached to the slide out. An electric one will have either a screw type device or a section with gear teeth on it that a gear turned by the motor pulls the slide in or out. Let us know what you find out.