I have a 1952 mercury and I am curious if when I’m going to stop or slow down if I need to take it out of overdrive before doing so. The overdrive relay does not work in this car so I rigged up a switch that I can use to turn the overdrive on after reaching about 30 mph. I do turn it off before stopping or slowing down. Am I doing anything wrong?
No. That should work fine.
I think some English sports cars had a switch to energize or de-energize the overdrive. You are doing the same thing. BTW, I always liked the Borg-Warner overdrive unit that is on your car. For a car that did lots of highway travel, it really extended engine life particularly for long stroke six cylinder engines.
I think you will be alright, however it will probably stay in overdrive even after you stop. It might make starting off a little less powerful.
Many of the old flat-head hot rodders mounted a switch on the shift lever and created a 6-speed that way…But the overdrive unit did not like being used in first gear especially behind a souped up engine…Today, they are rare and expensive …