I found this little gem on another board:
Dieseltrans.com :: View topic - RATACHETTING IN REVRESE
"This thread just brought to mind when the master builder that trained me, Odell, had a stuck valve in the governor circuit he would at 50mph try to engage the park mechanism. It would rattle so bad it would unstick the valve. If you had dentures, heaven help you because it would rattle them loose at the same time. I wouldn’t in a million years do that, with my luck it would either engage park or reverse. I still prefer to do it the old fashioned way,take out the valve and clean it."
Dieseltrans.com :: View topic - RATACHETTING IN REVRESE
"This thread just brought to mind when the master builder that trained me, Odell, had a stuck valve in the governor circuit he would at 50mph try to engage the park mechanism. It would rattle so bad it would unstick the valve. If you had dentures, heaven help you because it would rattle them loose at the same time. I wouldn’t in a million years do that, with my luck it would either engage park or reverse. I still prefer to do it the old fashioned way,take out the valve and clean it."