[77newell]

While the explanations I gave in the two messages above remain valid, following some research I've realized there are two more possibilities for the symptoms described in the original post (again assuming a mechanical governor).

The focus is the buffer switch mounted on the side of the governor. During shutdown, the stop engine actuator pushes out on the same linkage that actuates the buffer switch to turn the Jakes on. This is OK since fuel is shut off by the actuator. Though it has never happened to me I believe it is possible that the rod actuating the buffer switch could get stuck in the actuated position following shutdown of the engine. Pushing it back in and then trying to see if a cycle of acceleration/decelleration results in normal operation would test if this was an aberration or if the buffer switch assmebly needs replacing.

The other possibility is that the when actuated during shutdown the contacts in the buffer switch managed to weld themselves together. The test for this would be that whenever the dash switch is turned on the Jakes come on immediately AND when electrically testing for resistence across the buffer switch in the unactuated position (see paragraph above to determine that it is unactuated) there is infinite resistence or what is known as an open.

If as I understand the symptoms went away during the day's drive (that is the Jake switch turned on and things operated normally) I would suspect that the actuator hung up during shutdown and the following day the warming of the engine and vibration caused it to return to normal.

If the symptoms reappear I would proceed as follows: check that the actuating rod for the buffer switch is not stuck in the out position, if it is not then check for welded contacts in the switch, if they are not then readjust the buffer switch as described in the Jacobs manual.