The parking brake will not engage on my Model 135 mower. The foot-operated brake itself works OK. The orange plastic parking brake handle on the dashboard seems to be intact but the metal rod that leads down to the brake mechanism from that handle won't move up or down. The brake safety switch is in place and seems to be working. I suspect something is jammed in the area under the engine compartment but have no idea what to look for or how to get under there for an inspection. It could be something as simple as a rock or bit of tree branch that has become wedged. I'd appreciate any suggestions that would keep me from having to send the mower to the local JD dealer. Thanks.